In the occasion that I write this blog, the world is joyfully commemorating Christmas. One prominent facet of this blissful season is the Star that shone the brightest when the Messiah was born in Bethlehem.

Ever wonder how the distant stars and even the Christmas lights here on earth generate light? This must have something to do with what happens to the atoms that make up these bright objects. I prepared here a PowerPoint presentation for you to see how an atom produces light.

<iframe src=”http://docs.google.com/present/embed?id=dcwg6h8f_50cr6692gm&size=m” frameborder=”0″ width=”555″ height=”451″></iframe>

view here

The stars continue to shine for as long as the electrons in their myriad atoms are excited by energy. Our star, the sun, gets its energy from the nuclear reaction of hydrogen. Provided that the hydrogen nuclei are still present, the sun, and all the stars in the universe will shine persistently.

Have a bright Christmas and a shining New Year!

Using a great power point I found online, I created this atomic model timeline foldable to go along with it. The person who made the ppt, used images from the BrainPOP movie for the atomic models and scientists, and an image of Bohr from an episode of the Simpsons .  I photocopied it so that it would be 2-sided. The students then folded it in half using the ”hot dog” fold and cut along the dotted lines to make flaps that lifted.

As we discussed the power point, they took bulleted notes on the flap for each model/scientist.  We also talked about how Bohr worked on the Atomic Bomb during WW2, about Einstein’s letter to Roosevelt, the race against the Germans to build the first atomic bomb, and the bombing of Japan.  Next time we meet, I want to show some quick  video clips from the movie “Fat Man, Little Boy” and actual footage from the Trinity testing.

One of my personal goals this year was to incorporate more history and information about these fascinating people into our studies.  In the past I always felt like I didn’t have enough time, but this year I am weaving it in and it doesn’t really take up as much time as I thought it might.

After break, I will take some pics of completed timelines and the jigsaw activity we did with notes from the BrainPOP Movie.

Here is the timeline: Atomic Model Timeline Foldable

A Milwaukee city school teacher has assaulted a little first grade African-American girl in front of her class, by aggressively cutting off her French braids because she wanted the child to stop playing with her hair!

What is more surprising about this story is that her mother calmly went to the school to discuss the assault on her child, and when the teacher became indignant, she quietly left the classroom, to discuss the matter competently with the principle.

That is a good thing, and a good example for us all,…especially me. I commend her in her measured approach to this assault on her daughter’s hair.

I say this because, I probably would have handled it differently.

I remember a situation that happened to my brother, when he was in elementary school.

Apparently, the principle at his school, had taken it upon himself to spank my brother with a paddle, for some minor infraction, and to top that off, he was spanked in front of his classroom.My brother was in the third grade, and this was the late 60’s, not that long after black people had received our civil rights.

My dad , upon learning of this news, rushed to the school, that was not too far from our house, and immediately began a violent beat down of the principle, because he was upset over what he saw as a physical attack on my brother.

It was a traumatic situation for all involved, but no one was incarcerated  for any of it, the principle was reassigned,and I believe that my father got his point across.

My dad became a neighborhood legend for that beat down, and people still talk about it to this day.

Now, this assault on little Lamya Cammon, has similar overtones.

Lamya has a french braid hairstyle, quite nice I must say,…and she has a lot of beautiful beads that adorn her braids, and they dangle. Being a 7-year-old child, Lamya would twist twirl and fidget with the beads, like a little kid would do.

Lamya Cammon...teacher assaulted her and cut off her hair

The teacher, having a bad day, asked her to stop playing with her hair, and Lamya probably did not at the level that satisfied the teachers demands.

Lamya Cammon says the teacher called her up to the front of the class at Congress Elementary, took a classroom scissors and snipped the beaded braid that frames her face.

“I went to my desk and cried. They was laughing.  She threw it away.” Cannon said.

The teacher also went on to ridicule Lamya, and mocked her by telling her …..”now you can go home and tell your mother I did it”….and…”what you going to tell your mom now”… just to taunt her.

Cammon’s mother,Helen Cunningham, is furious. She went to the school and confronted the teacher, and she was able to keep her composure, unlike the approach that my father employed.

“I said, ‘Well, you know, you cut a lot of her hair off.’ And she was like, ‘Well, I do apologize.’ She said, ‘But I was frustrated,’” Cammon’s mother, Helen Cunningham, said.

Frustrated?…a first grade teacher at a public elementary school will be frustrated from time to time, because that goes along with the territory of teaching little kids.

I would hope that the teacher could source some patience and professionalism, and above all, keep their hands off of the children. There is no school district that I know of in America, that continues to spank children as a disciplinary action.

I find it highly inappropriate for any teacher to lay their hands on a child in their class, and in turn the students have no right to disrupt the class or physically abuse anyone there.

The teacher should have called Lamya’s mother, way before she resorted to cutting off her hair.

A report from Chicagonow.com states that… the teacher may face disciplinary action, but has not been removed from the classroom.

When the District Attorney’s Office said there were not grounds for criminal charges, police issued the teacher a $175 dollar ticket for disorderly conduct.

Ironically, the teacher received that weak punishment, but Lamya  has been moved to another class which separates her from her school friends, that she has bonded with for the past 2 years.

I call for the dismissal of this unnamed teacher, and I believe that if spitting at someone is a felony assault, then cutting ones hair , a physical crime, is far worse than that.

The school system has made statement about budget cuts causing mounting frustrations on the teachers, as a rationale for the assault.I say that if this is the case, then that school system should be taken over by the feds, so that they can put in place some competent oversight of the school system, and to hire some professionals to teach the children there.

As it stands now, Lamya has received the short end of the stick,and I have to wonder that if she was not black, then this  assault on a child by a teacher would be an even bigger story, with the appropriate charges, not this non-charge, being levied on this rogue teacher.

I see that for $175.00, which is the fine for a disturbing the peace ticket in Milwaukee, that the teachers there can physically assault and abuse our children at will.

I believe that my father’s approach, although not as refined as some would prefer, got more effective results from the school system, and served as a better deterrent than $175.00…which, even in these times of recession, still is not a lot of money.

I want the mother’s out there to comment on this case. What would you do if this were your daughter?….regulate the situation like my father….or what?…I do not think this minor fine will serve as any deterrent for this form of physical humiliation and assault on a little girl, to happen again.

Sources…

http://blogs.bet.com/news/newsyoushouldknow/frustrated-teacher-cuts-students-hair/

http://www.wkowtv.com/Global/story.asp?S=11677405

http://www.chicagonow.com/blogs/message-from-montie/2009/12/seven-year-old-lamya-cammon-gets-hair-cut-off-by-milwaukee-teacher.html

The two slit experiment was one of the first verifiable physical phenomena that really forced physicists and eventually the lay person to allow for the possibility that the world might not be “what it seems”. Einstein’s Special and General Relativity shook the foundations of intuition and “common sense” in the macroscopic universe, and though counter intuitive and hard to comprehend, Quantum Mechanics as described by Planck, Bohr, Schrödinger, and Heisenberg forces one to suspend all disbelief. Quantum Mechanics describes and accurately predicts verifiable physical phenomena. The two slit experiment was one of the seminal works in Quantum physics and its results defy accepted notions of reality. The progenitor of the two slit experiment was the long standing debate whether or not light was a particle or a wave. Newton held that light was a collection of discrete particles, but from his death until the beginning of the twentieth century, more and more evidenced was obtained that lead to the conclusion that light was indeed a wave, diffraction experiments had shown conclusively that light exhibited wave like properties as described by Maxwell’s Electromagnetic Wave Theory. However, in the early 20th century, Einstein published a paper describing the photoelectric effect, proving that electrons emit a proton when changing energy levels. The question of whether light was a wave or a particle was opened once again. Light seemed to have both the properties of particles and waves, an absurd notion that was verified empirically. The solution to this contradictory interpretation was discovered by Louis de Broglie, a French physicist who described mathematically a relationship between the momentum of a particle and a wave length at the quantum level: p = h/λ, where p is the particles momentum, h is Plank’s constant and λ is the wavelength. Considering that a photon has no mass, this result, though somewhat confounding, can be accepted without a compromise of empirical reality. The two slit experiment attempted to determine whether or not an electron was a particle or a wave. The experiment is as follows: electrons are produced from a source and fired at a screen with two slits. The slits can be opened or closed. If one slit is open, the resulting pattern on the screen is consistent with classical mechanics; the distribution reflects the accepted notion that electrons were particles. However, when both slits are open, electrons are fired through the slits and the resulting distribution pattern looks like the intensity of a light wave, rather than a collection of singular impact points that would be expected if the electrons were hitting the screen as individual particles. If a large amount of electrons are used, it is possible to conclude that the probabilistic distribution of a high intensity of electrons is in the same pattern as an electromagnetic wave. Waves are distributed in a pattern such that the variation of wave lengths and amplitudes interfere, either destructively or constructively, leaving a definable pattern (in classical mechanical terms) on the screen behind the slits. However, if the experiment is repeated, now with the flow of electrons lowered such that only one particle is going through a slit at one time, the same pattern of wave like behavior is detected on the screen. The pattern of interference is still present, and the only conclusion is the preposterous: each particle interferes with itself. Quantum Mechanics was founded on such experimental results. The nature of the Quantum world is one of probabilities; positions of quantum particles past certain points are wholly indeterminable. Schrödinger mathematically defined the strange interpretation of the atomic world of Bohr with a set of differential equations with the ψ function. These equations described electrons in the form of a wave function, which reconciled the strange results of Plank’s results and de Broglie’s hypothesized relationship between momentum and wave length. Once an experimental measurement has been made, Schrödinger’s wave function “collapses” i.e. the probability becomes an actuality, and the wave like behavior of the electron or any other quantum particle, is annihilated and the particle itself is now identified as such.

In this page You will find some hobbistic works related to physics

“- Por mi parte- comentó Niels-, puedo estar muy de acuerdo con los positivistas acerca de lo que pretenden, pero no acerca de lo que rechazan. Todo lo que intentan hacer los positivistas es dotar a los procedimientos de que se vale la ciencia moderna de una base filosófica, o si se prefiere, de una justificación. Ponen de relieve que las antiguas filosofías carecían de una auténtica precisión de conceptos científicos, y piensan que la mayor parte de las cuestiones que plantean y tratan los filósofos convencionales no tienen ningún sentido en absoluto, que no son más que pseudoproblemas, y que, como tales, lo mejor es ignorarlos. Por supuesto, esta insistencia de los positivistas en la claridad conceptual es algo que yo respaldo plenamente, pero el hecho de considerar prohibida toda disquisición en torno a temas más amplios, sencillamente porque estos dominios carezcan de conceptos lo suficientemente definidos, no me parece demasiado útil: esa misma prohibición podría impedirnos comprender la teoría

(…)

- Tampoco a mí me parece útil esa forma de restringir el lenguaje -dijo Niels-. Todos conocéis el poema de Schiller “Sentencias de Confucio”, que contiene aquella frase memorable: “sólo una mente plena es clara, y la verdad habita en las profundidades”. En nuestro caso, una mente plena no se compone sólo de una abundancia de experiencia, sino también de una abundancia de conceptos con los que poder hablar de nuestros problemas y de todos los fenómenos en general.”

“La verdad habita en las profundidades”, en Más allá de la física. W. Heisenberg.

Un paseo por la Historia de los modelos atómicos. Observad como se suceden los acontecimientos, cada dos años, más o menos, se producen nuevas teorías respecto al átomo.

M ATÓMICO DE BOHR al MCUANTICO

Para ver bien los texto de la siguiente imagen, pincha en ella.

En el siguiente vídeo veras un paseo rápido por los diferentes modelos atómicos.

3.1 Probing matter

3.1 Probing matter -worksheets

Constituents of the Atom

The Photoelectric Effect

Wave-Particle Duality

Electrons and Atoms

Structure of the Atom

Nuclear Changes

Observing the Photoelectric Effect

Explaining the photoelectric effect

Models of the Atom

3.1 Probing matter -video tutorials

Rutherford Experiment

Bohr Model of the Atom

De Broglie Wavelength

3.1 Probing matter -videos

Ernest Rutherford

The Atomic Nucleus

Is Light a Particle

Atoms Absorb and Emit Light

Photoelectric Effect

3.1 Probing matter -animations

 Essa história parece ser chata, mas tenha certeza que é muitíssimo interessante…! 

                                   ” Um professor de Física, no começo do século XX, relatou a seguinte experiência:

“Há algum tempo, recebi um convite para servir de árbitro na revisão de uma prova de Física. O professor queria atribuir-lhe nota “zero”. O aluno contestava tal conceito, alegando me merecia nota máxima. Professor e aluno concordaram em submeter o problema a um juiz imparcial, e eu fui o escolhido.

Li a questão da prova: “Mostre como determinar a altura de um edifício bem alto com o auxílio de um barômetro”. A resposta do estudante foi a seguinte:

“Leve o barômetro ao alto do edifício e amarre nele uma corda; baixe o barômetro até a calçada, em seguida levante e meça o comprimento da corda; este comprimento será igual à altura do edifício.”.

O estudante tinha razão, pois a resposta satisfazia o enunciado, de certa forma, completa e corretamente. Entretanto, se ele tirasse nota máxima, estaria caracterizada sua aprovação em um curso de Física, enquanto a resposta não confirmava isso. Sugeri então conceder uma nova chance ao estudante: ele teria seis minutos para responder a questão, e sua resposta deveria mostrar, necessariamente, algum conhecimento em Física.

Passados cinco minutos, ele ainda não havia escrito nada. Perguntei-lhe então se desejava desistir, mas ele respondeu que havia muitas respostas para o problema e estava escolhendo a melhor entre elas. Desculpei-me pela interrupção e solicitei que continuasse.

No momento seguinte ele escreveu esta resposta:

“Vá ao alto do edifício. Da ponta do telhado, solte o barômetro, medindo o tempo t de queda até o solo. Depois, empregando a fórmula: h= gt²/2, calcula-se a altura do edifício.”.

Perguntei então ao meu colega se ele estava satisfeito com a nova resposta. Ele disse que sim, e atribuiu nota máxima à prova, ainda que houvesse uma expressão de descontentamento, talvez inconformismo.

Ao sair da sala, lembrei-me de que o estudante afirmara ter outras respostas para o problema. Embora já sem tempo, não resisti à curiosidade e perguntei-lhe quais eram as respostas.

- Ah, sim! – Disse ele. – há muitas maneiras de se achar a altura de um edifício com a a juda de um barômetro.

Perante a minha curiosidade e a já perplexidade do meu colega, o estudante desfilou as seguintes explicações:

- Por exemplo. Num belo dia de sol, pode-se medir a altura do barômetro e o comprimento de sua sombra projetada no solo. Em seguida, mede-se o comprimento da sobra do edifício. Com o uso de uma simples regra de três, obtêm-se a altura do edifício.

“Se desejar um método mais complexo, amarre o barômetro na ponta de uma corda e balance-o como um pênduro, o que permite a determinação da aceleração da gravidade (g), no topo do edifício e no nível da rua; a partir da diferença dos valores de g, a altura do edifício pode ser calculada.”

“Finalmente” – concluiu. – “Se não for cobrada uma solução física para o problema, existem outras respostas. Por exemplo, ir até o síndico e dizer-lhe: - Caro síndico, esse belo barômetro pode ser seu se o senhor me disser a altura deste edifício”.

Não sem alguma perplexidade, perguntei ao estudante se ele não sabia qual era a resposta “esperada” para o problema. Ele consentiu que sabia, mas que também já estava farto das repetidas tentativas dos professores em definir-lhe como ele deveria pensar”.

_______________________________________________________

É desconhecida a autoria dessa interessante história. Há uma versão atribuida ao Físico R. Feinman. Outra, em francês, dá conta que Niels Bohr foi o aluno e Rutheford o professor. Ambos se tornariam Prêmio Nobel de Física. o Dr. Alexander Calandra, professor na cidade americana de St. Louis, publicou, em 1966, um conto inspirado em historieta lida na revista Readers Digest, em 1958. Se aceita, contudo, a probabilidade de que o relato teve origem em fato real.

Fragmento:

Modelo de bandas de energía en los sólidos.
Los niveles de energía de los electrones en los átomos de un cristal no son iguales a los niveles de energía de los electrones para átomos aislados. Normalmente se pueden despreciar las interacciones de unos átomos con otros ya que los niveles de energía no se ven afectados, sin embargo en un cristal el campo eléctrico producido por los electrones de los átomos vecinos afecta y modifica los niveles energéticos de los átomos a sus alrededores…

>>Descargar PDF<<

These are certainly not my own words… Though I have replaced my own name within their framework of wisdom. And there is a reason for doing this…

And, as if to Know and Embrace this Wisdom that Toporek helped me to discover, I just had to copy out his beautiful flow of words and add my own name in there as an affirmation of this freedom of Self.

“So, tell me Karl, what are you going to be when you grow up?”

The Scream, by the Norwegian artist Edvard Munch... A feeling I've felt before.

As a child, it always bothered me when an grown-up asked me that question. And being so young and naïve, I didn’t know exactly why it bothered me so much… But today, with a little more headroom on my shoulders, I think I’m beginning to understand why it did, and still does, bother me…

The only absolute certainty is uncertainty itself.

According to legend, it was this assertion that prompted the Delphic Oracle to recognize Socrates as the wisest man in Greece. Socrates replied that he possessed no wisdom whatsoever, but paradoxically the Oracle interpreted his unapologetic acceptance of ignorance as evidence of great wisdom. The pride of many prominent Athenians was wounded by the idea of being ranked below this self-proclaimed ignorant, so he was accused of corrupting the young, and was sentenced to death by poisoning.

2,000 years after Socrates’ execution, at a point in time between the birth of Descartes and the death of Kant, the West became helplessly enamored with certainty. Calculus became the fundamental discipline that helped us understand and define reality with great accuracy, even when it was ineffective at amicably resolving the battle between Leibniz and Newton regarding its discovery.

According to Lao Tzu, what is true can’t be described, but after Newton’s discoveries of gravity and the laws of motion, it was hard not to be convinced that reality could be outlined and explained through scientific exploration. Newton was followed by Bernoulli, Coulomb, Avogadro, Fourier, Faraday, Kelvin, Joule and Maxwell, and with every new discovery the certainty that the universe could be completely understood through the reductionism of equations grew ever stronger. The prevalent scientific posture after Maxwell’s unification of electricity and magnetism was that at the end of the 19th century “all the great physical constants would have been approximately estimated, and the only occupation left to men of science would be to carry these measurements to another place of decimals”. Of course history had different plans, and a new batch of scientists that included Curie, Rutherford, Planck, Einstein and Bohr proved that the universe was not that simple to figure out. Radioactivity, the equivalency between energy and matter, the relative flow of time, and light behaving as both wave and particle were a few of the new discoveries. During the 20th century each new finding increased the level of uncertainty, but the final blow to the dream of absolute scientific determinism came in 1926, when a young German physicist proved that it was impossible to know the position and momentum of a particle at the same time. At the age of 25, Werner Heisenberg formulated the Uncertainty Principle, laying the foundation of what became known as the Copenhagen Interpretation of quantum mechanics. The implication of this discovery was that unpredictability ruled at the fundamental level of subatomic particles. The principle imposed a very real physical limitation on human knowledge, one that could not be overcome by technology. At an elementary level, scientists were doomed to predict only probabilities, never actual outcomes. Einstein strongly disliked this conclusion and died trying to disprove it, but years of experimental consistency confirmed his worst fears: God does play dice.

In 1932 Heisenberg was awarded the Nobel Prize in Physics. Since then, the description of reality has only gotten stranger and more uncertain. Some of the latest scientific breakthroughs, like the discovery of Quantum Entanglement, seem to imply that not only is time an illusion, but locality as well. Recent discoveries by Leonard Susskind, Juan Maldacena and Ed Witten support the idea that we live in a holographic universe and that, despite its apparent solidity, objective reality does not exist. According to the Holographic Principle, objective reality is just a mirage created in our brains based on sensorial input; its our way of interpreting an otherwise undifferentiated, infinitely interconnected and splendidly detailed hologram. In this universe, all aspects of reality are merely interpretations relative to the observer, making it impossible to reach any kind of universal certainty.

It took 2,500 years, but Socrates was finally vindicated: The only absolute certainty is uncertainty itself!

So now we return back to this troubling question… “So, tell me Karl, what are you going to be when you grow up?” As I grew older I would get the same uncomfortable feeling when, at a job interview, I was asked “where do you see yourself in 5 years?” I even found it utterly uncomfortable when a priest prompted a young couple to promise eternal love to each other.

At some point I started to realize that, in most cases, the people asking me these questions were just trying to satisfy their own expectations with my answers, and that very often I would provide the expected response just to keep them at ease. Many of the people striving for certainty just want the confirmation that their particular belief system is legitimized; confirmation that a son will be a doctor and not an ballet dancer, confirmation that a partner will never behave in a way that may threaten the marriage, confirmation that a couple’s public commitment will continue to validate the church’s authority.

Today I know that the uncomfortable feelings those questions arouse in me had little to do with any particular answer, and a lot to do with the questions themselves; that I do not want my future to be seen as a means to validate someone else’s expectations, that by answering I am turning myself into a potential liar, and that the only honest answer to such questions is, and should have always been, I DON’T KNOW. Any other answer would represent a self-imposed compromised fate, a voluntary limitation of my own freedom, an imposition of countless personal and communal hopes and fears over the limitless possibilities of reality.

I DONT KNOW may not be the most romantic or reassuring answer, but it is often the most honest. Unfortunately more people today want to be right rather than honest. Through schools, temples and popular culture we are taught to perceive certainty as a virtue. The preacher narrates Biblical events as if he had experienced them himself, and talks about the afterlife as if he had already been there and back; the science teacher talks about subatomic particles as if he had actually seen them; and all over the world celebrities are admired for their apparent confidence and self assurance (heck, if Bono gets behind this cause it must be important). Recently we have experienced a string of international leaders that are far more concerned with appearing to be right than with actually doing the right thing.

Religion manufactures certainty from the past and imposes it over the present, while present science places its faith in future technologies to increase its own certainty. Everyone holding a position of authority refuses to display signs of ignorance for fear of appearing weak or conceding.

I am not afraid of doubt, but I am terrified by the recent resurgence of certainty and fundamentalism. Doubt can bring about humbleness, while certainty can lead to arrogance. Some of the most horrific episodes in history are those involving arrogant madmen.

Instead of allowing perception to be informed by experiential reality, a madman will try to force reality to conform to his prejudice. He will try to impose an order on reality and will attempt to destroy any element that challenges such order. But chaos is the reality of nature, while order is just the dream of men. Inevitably, one man’s dream will become another man’s nightmare, and our attempts to impose an artificial order on reality will often end up in despair and destruction.

Expectations are futile, control is a painful illusion, we are made of uncertainty. Let chaos be and order will naturally emerge; strive for order and you will live in chaos. How do I know this?

I DON’T KNOW…

If you would like to find out more about Toporek and his work, please click here.

¿Qué es una serendipia?

Esta rara palabra importada del término anglosajón “serendipity” y derivada a su vez de la palabra sánscrita “swarnadip” ha salpicado frecuentemente la historia de la humanidad y su progreso…

El neologismo, acuñado en 1754 por el escritor Horace Walpole, ha ido cayendo en desuso desde entonces pero durante los últimos años y gracias a la película homónima protagonizada por John Cusack y Kate Beckinsale ha logrado encontrar cierto hueco léxico.

Hay cierta linealidad entre conformidad y casualidad...

Para que os hagáis una idea algunos de sus sinónimos en nuestro idioma podrían ser chiripa, potra o carambola; y es que el término hace referencia a aquellos descubrimientos normalmente científicos y tecnológicos que no eran el objetivo original y se alcanzan en buena parte gracias a la casualidad.

Y es que fortuitos en mayor o menor medida los ha habido y muchos: el Principio de Arquímedes, la manzana de Newton, la penicilina de Fleming pertenecen a una larga lista de serendipias que han sorprendido, sorprenden y sorprenderán a propios y extraños.

Para que no me llaméis rácano ( ) u otras lindeces os voy a contar algunos de los ejemplos más famosos pero no necesariamente los más conocidos:

- Cuenta en sus memorias el químico Friedrich Kekulé que mientras volvía una tarde en el autobús se quedó dormido y, producto de la obsesión de llevar muchos años tras la estructura de la molécula del benceno, comenzó a soñar con átomos que danzaban y chocaban entre ellos. Varios átomos se unieron, formando una serpiente que hacía eses y de repente la serpiente se mordió la cola y Kekulé despertó. A nadie se le había ocurrido hasta ese momento que pudiera tratarse de un compuesto cíclico.

- Otra historia curiosa es la de la invención de las notas Post-It de la multinacional 3M. En 1968 el investigador de la compañía Spencer Silver estaba buscando un adhesivo potente pero en cambio logró accidentalmente uno débil al cual no logró darle ninguna utilidad. Casi una década después a Arthur Fry, un colega suyo, se le ocurrió usar aquel adhesivo para crear notas que no se cayeran de su himnario del coro de la iglesia mientras lo hojeaba.

Seguramente el cachondo de Arthur Fry ha pasado de no saber qué hacer con tanto pegamento defectuoso a no saber que hacer con tanto dinero...

- A mediados del siglo XIX, se intentó buscar un material para sustituir el marfil de las bolas de billar. En 1870 John Wesley Hyatt, un inventor estadounidense, estaba prensando una mezcla de serrín y papel con cola, porque creía que así conseguiría el nuevo material pero se cortó un dedo y fue a su botiquín. Sin querer volcó un frasco de colodión (un compuesto que se utiliza como aglutinante en cirugía) y provocó que quedara en su estantería una capa de nitrocelulosa. Al verla, Hyatt se dio cuenta de que este compuesto uniría mejor su mezcla de serrín y papel en lugar de la cola se culminó la invención del celuloide.

- El físico Hans Christian Oersted demostró por casualidad algo que había predicho teóricamente pero no se había comprobado: que existía una relación entre la electricidad y el magnetismo. Un día mientras trabajaba en su laboratorio dejó la aguja del compás perpendicular a un cable por el que pasaba corriente eléctrica y descubrió que esta se desviaba considerablemente debido al campo magnético generado por la electricidad.

- También la invención del microondas es serendípica: Percy Spencer era un ingeniero de Raytheon Inc., el principal fabricante de magnetrones de la Segunda Guerra Mundial (se usan para la fabricación de radares). Un buen día mientras trabajaba con uno de ellos descubrió con sorpresa cómo un chocolatina que llevaba en el bolsillo para almorzar se había derretido al estar trabajando al lado del radar . Esto le llevó a pensar en el revolucionario uso doméstico de este aparato para calentar la comida.

¡Nunca calentar el café por las mañanas fue tan fácil!

En fin, como véis hay multitud de ejemplos y este podría ser el post más largo de la historia de Internet pero bueno, tampoco quiero ser tan ambicioso… Y es que la clave enigmática de las serendipias bajo mi punto de vista es determinar si muchas son puro producto de la casualidad o son cosas que estaban “destinadas” a pasar. Ojo que la entrecomillo porque no me refiero al concepto clásico del destino y de que todo está escrito si no algo más en la línea de lo que decía Louis Pasteur: “La suerte favorece a la mente preparada”.

Op hierdie blog het ek en Joh al meermale geworstel met die hoër geestelike dinge en die onmoontlikheid daarvan om deurmiddel van die rede, die transendente te deurbreek en so direk met die immanente in “verhouding” te tree.

Die probleem met ons benadering, en dus geregverdige kritiek wat ons op die hals geloop het, is dat ons a priori aanvaar dat daar wel `n transendente werklikheid bestaan wat deurgebreek kan/moet word.

Die teenargument hou dit dat: 1) Net die fisiese werklikheid bestaan en 2) met die verstand, die rede kan ons alle verskynsels in hierdie werklikheid verklaar.

Om die werklikheid te omskryf, moet ons woorde gebruik. Joh het al vanuit sy Buddhistiese perspektief die tekortkominge van hierdie metode uitgewys.

(Die volgende stukkies inligting kry ek uit ‘The Dancing Wo Li Masters’ van Gary Zukav wat in die jare 80 so `n opskudding veroorsaak het.)

Bell se teorie verwys ook na die probleem as hy sê: “Words are not real things. They are only symbols representing something else. Symbols and experience do not follow the same rules.

Hapiness is a concept, is a state of being, is an experience.

A description of a state of being is a symbol.” En die simbool is nie die ondervinding nie. Dit dui op, maar is nie die ondervinding self nie.

Die Fundamental Physics Group (waarvan Niels Bohr en Einstein lede was) het reeds in 1927 besluit dat dit heel moontlik nie moontlik sal wees om `n model van die werklikheid daar te stel nie aangesien “Knowledge itself is limited.” Niels Bohr se Copenhagen Interpretasie van Qauntum Meganika sê duidelik dat; “Mind deals only with ideas.” Dit is nie waar is om te dink dat “mind can actually ponder reality” nie. Die verstand kan slegs idees omtrent die werklikheid oordink.

Bohr gaan dan verder en sê dat “a complete understanding of reality lies beyond the capabilities of rational thought” en verwerp so die aanname dat die werklikheid verstaan kan word in terme van elementêre “space-time realities.” (Einstein het geweier om die omskrywing te onderskryf).

Max Plank sê die wetenskap beteken “…unresting endeavor and continually progressing development toward an aim which the poetic intuition may apprehend, but which the intellect can never fully grasp.” (my kursief)

Hierdie stelling maak vir my pragtig sin, en word uitstekend geïllustreer deur Einstein se “ultimate vision” waarin hy (redeloos?) geglo het, maar nooit kon bewys nie.

Volgens Einstein is;

“A piece of matter is a curvature of the space-time continuum.

There is no such thing as “gravity” — gravity is the equivalent of acceleration, mental creations. No such things exist in the real world. There is no such thing as “gravity” — gravity is the equivalent of acceleration, which is motion. There is no such thing as “matter”, — matter is a curvature of the space-time continuum. There is not even such a thing as “energy”, — energy equals mass sand mass is space-time curvature.

What we consider to be a planet with its own gravitational field moving around the sun in an orbit created by the gravitational attraction (force) of the sun is actually a pronounced curvature of the space-time continuum finding its easiest path through the space-time continuum in the vicinity of a pronounced curvature of the space-time continuum!

There is nothing but space-time and motion and they in effect, are the same thing.”

Aanhangers van die suiwer materialisme het dus eintlik geen been om op te staan nie —– hulle het inderdaad nie eers `n planeet om op te staan nie, want selfs die planeet het geen substansie nie!

Om die spyker nog verder in die kis te slaan sê die Quantum Field Theory dat:

Physical reality is essentially no substantial, fields alone are real. They are the substance of the universe and not “matter”. Matter (particles) is simply the momentary manifestations of interacting fields which, intangible and insubstantial as they are, are the only real things in the universe.

Miskien nog die heel interessantste uitspraak kom van die Fisikus E H Walker wat op grond van die bekende “double-split” Photon eksperiment opgemerk het:

“Consciousness may be associated with all quantum mechanical processes ….. since everything that occurs is ultimately the result of one or more quantum mechanical events, the universe is “inhabited” by an almost unlimited number of rather discrete conscious, usually non thinking entities that are responsible for the detailed working of the universe.” (Hoor ek `n gejuig opgaan vanaf die Intelligente Ontwerp geledere?)

Dit wil my dus voorkom asof kennis aangaande die “werklikheid” wat, volgens sommige fisici, totaal nie-substansiëel is, nie deur die rede of deur laterale denke alleen bekom kan word nie, maar wat veral nodig is, is transendente denke sodat ons soos Einstein in die hysbak sal klim, dalk `n Damaskus ervaring beleef en dan sal “weet” E = mc² is lank nie die einde van die storie nie!.

En wie weet, as jy die wêreld as totaal insubstansiëel kan beleef, dan kan jy dalk net tog op water loop, water in wyn verander, soos die Buddha, Liewe Jesus en Baal Shem Toff na bewering op meer as een plek gelyktydig verskyn?

2 hr sermon by Stephen Bohr

Click here

Voy a empezar a promocionar libros en este blog, y comienzo con esta maravilla: “El placer de descubrir”, una recopilación de entrevistas, conferencias y artículos del gran físico del siglo pasado, Richard P. Feynman, Premio Nobel de 1965, de quien ya he hablado en varias ocasiones, y que para mi es el modelo a seguir en ciencia.

La grandeza de Feynman no se debe solo a sus descubrimientos sobre electrodinámica cuántica o a que sea, como le bautizaron, el “padre de la nanotecnología”. Su grandeza se debe a que todos sus pasos los dio con gran humor, imaginación y humildad, hasta el punto de que uno de los libros que tratan sobre él se titula: “¿Está usted de broma, señor Feynman?”.

En “El placer de descubrir” podremos aprender mucho sobre cómo debe pensar alguien verdaderamente interesado en descubrir, y trata los siguientes temas:

Infancia:

En varios capítulos descubrimos cómo desde pequeño fue educado por su padre para amar la ciencia, dando paseos por el bosque y analizando cada minúsculo detalle, jugando con secuencias lógicas de colores y números, y analizando la mecánica clásica con un simple coche de ruedas:

Un día estaba yo jugando con lo que llamamos un vagón exprés (…). Tenía dentro una bola (lo recuerdo bien) y me fijé en un detalle del movimiento de la bola, así que le dije a mi padre: “Papá, he notado algo: cuando tiro del vagón la bola rueda hacia la parte trasera, y cuando estoy tirando y de repoente dejo de hacerlo, la bola rueda hacia la parte delantera (…), ¿por qué pasa eso?” (…) “Nadie lo sabe. Hay un principio general que dice que las cosas que están en movimiento tratan de seguir en movimiento, y las cosas que están en reposo tienden a permanecer en reposo a menos que ejerzas una fuerza sobre ellas (…). Esta tendencia se llama inercia pero nadie sabe por qué es verdad. (…) Si te fijas bien verás que no es la bola la que rueda hacia la parte trasera del vagón, sino que es la parte trasera del vagón la que tú estás tirando hacia la bola; verás que la bola sigue quieta o que quizá empieza a moverse debido a la fricción, pero en realidad se mueve hacia adelante y no hacia atrás.”

Asimismo, podemos incluir en su época joven experimentos acerca de si es posible o no contar mientras se lee o se habla, con resultados interesantes.

Participación en el Proyecto Manhattan:

De su participación en el proyecto de la bomba atómica podemos encontrar un joya de capítulo en este libro, donde Feynman nos cuenta cómo era la estancia en Los Álamos, y un sinfín de anécdotas: cómo consiguió tener una habitación para él solo, cómo filtraba información “disimuladamente”, cómo aprendió a desvalijar cajas fuertes escuchando sonidos o probando con constantes universales, cómo tuvo algunos golpes de suerte para contestar adecuadamente en situaciones en las que estaba despistado, cómo consiguió ser la primera persona que vió una bomba atómica en fase de pruebas sin gafas de protección cubriéndose con la luna de un coche de la radiacción ultravioleta, cómo conoció al Premio Nobel Niels Bohr sin dudar en preguntarle si estaba loco, y más situaciones como la que sigue:

Y así llega el día, el primer día de la censura. ¡Teléfono! ¡Riiiiing! Yo: “¿Qué?” “Venga, por favor.” Yo voy. “¿Qué es esto?” Es una carta de mi padre. “Bien, ¿qué es?” Hay un papel rayado, y hay unas líneas con puntos: cuatro puntos abajo, un punto arriba, dos puntos abajo, un punto arriba, un punto debajo de un punto. “¿Qué es esto?” Yo dije: “Es un código.” Y ellos: “sí, es un código; pero ¿qué dice?”. Yo dije: “No sé lo que dice.” Dijeron: “Bien, ¿cuál es la clave del código; cómo lo descrifra?”. Yo dije: “Pues no lo sé.” Entonces ellos dijeron: “¿Qué es esto?”. Yo dije: “Es una carta de mi mujer.” “dice TJXYWZ TW1X3. ¿Qué es esto?” Yo dije: “Otro código.” “¿Cuál es la clave?” “No lo sé.” Dijeron: “¿Usted está recibiendo mensajes en clave y no la conoce?” “Exactamente. Juego con ellos. Les reto a que me envíen un código que no pueda descifrar, ¿ven ustedes? De modo que se inventan códigos y me envían mensajes sin decirme cuál es la clave.” Ahora bien, una de las reglas de la censura era que no iban a interferir en nada que uno hiciera normalmente en el correo. Así que dijeron: “Bien, usted va a tener que decirles que por favor envíen la clave con el mensaje.” Dije: “¡Pero yo no quiero saber la clave!” Dijeron: “Muy bien, nosotros sacaremos la clave.” Y llegamos a ese compromiso.

Reflexiones Éticas:

Encontramos también en el libro entrevistas y conferencias en las que Richard expone su opinión sobre cómo se está menospreciando la ciencia en la sociedad, y que es vergonzoso que las pseudociencias (astrología, tarot, sanadores…) ganen tanto terreno:

Pienso, y todos ustedes deben saberlo por experiencia, que la gente (quiero decir la persona media, la gran mayoría de las personas, la inmensa mayoría de las personas) son lamentablemente, penosamente, absolutamente ignorantes de la ciencia en el mundo en el que viven, y pueden seguir así. No quiero decir nada de ellos; lo que quiero decir es que pueden seguir sin que les preocupe lo más mínimo (sólo tibiamente) y cuando ocasionalmente ven la CP mencionada en los periódicos, preguntan qué es eso. Y una cuestión interesante de la relación entre ciencia y sociedad moderna es precisamente ésa: ¿por qué es posible que la gente en una sociedad moderna permanezca tan penosamente ignorante, y pese a todo razonablemente felíz, cuando hay tanto conocimiento al que no pueden acceder?

Conferencia “Hay Mucho Sitio al Fondo”:

Esta conferencia, que el libro reproduce integramente, le valió a Feynman el ya mencionado título de “padre de la nanotecnología”, pues en ella aseguraba, algo adelantado a su época, que en un futuro cercano sería posible usar los propios átomos para procesar cada bit de un ordenador, de modo que todos los libros del mundo podrían grabarse con láser sobre nada menos que 2/3 de la punta de un alfiler.

En resumen, es un libro interesante, sobre una persona muy interesante, y que cautivará a cualquiera que esté interesado en el tema.

It is impossible to imagine a more dramatic and horrifying combination of scientific triumph with political and moral failure than has been shown to the world in the destruction of Hiroshima. From the scientific point of view, the atomic bomb embodies the results of a combination of genius and patience as remarkable as any in the history of mankind. Atoms are so minute that it might have seemed impossible to know as much as we do about them. A million million bundles, each containing a million million hydrogen atoms, would weigh about a gram and a half. Each hydrogen atom consists of a nucleus, and an electron going round the nucleus, as the earth goes round the sun. The distance from the nucleus to the electron is usually about a hundred-millionth of a centimetre; the electron and the nucleus are supposed to be so small that if they could be crowded together it would take about ten million million on end to fill a centimetre. The nucleus has positive electricity, the planetary electron an equal amount of negative electricity; the nucleus is about 1850 times as heavy as the electron. The hydrogen atom, which I have been describing, is the simplest of atoms, but the atom used in the atomic bomb is at the other end of the scale.

Uranium, the element chiefly used in the atomic bomb, has the heaviest and most complex of atoms. Normally there are 92 planetary electrons, while the nucleus is made up of about 238 neutrons (which have mass without electricity), 238 positrons (which have positive electricity and very little mass), and 146 electrons, which are like positrons except that their electricity is negative. Positrons repel each other, and so do electrons; but a positron and electron attract each other. The overcrowding of mutually attracted and expelled particles in the tiny space of the uranium nucleus involves enormous potentially explosive forces. Uranium is slightly radioactive, which means that some of its atoms break up naturally. But a quicker process than this is required for the making of an atomic bomb.

Rutherford found out, about thirty years ago, that little bits could be chipped off an atom by bombardment. In 1939, a more powerful process was discovered: it was found that neutrons, entering the nucleus of a uranium atom, would cause it to split into two roughly equal halves, which would rush off and disrupt other uranium atoms in the neighbourhood, and so set up a train of explosions so long as there was any of the right kind of uranium to be encountered.

Ever since the beginning of the war, the Germans on the one side, and the British and Americans on the other, have been working on the possibility of an atomic explosive. One of the difficulties was to make sure that it would not be too effective: there was a fear that it might destroy not only the enemy, but the whole planet, and naturally experiments were risky. But the difficulties were overcome, and now the possibility, which scientists have foreseen for over forty years, has entered into the world of practical politics. The labours of Rutherford and Bohr, of Heisenberg, and Schrödinger, and a number of other distinguished men, the ablest men of our time, and most of them both high-minded and public-spirited, have borne fruit: in an instant, by means of one small bomb, every vestige of life throughout four square miles of a populous city has been exterminated. As I write, I learn that a second bomb has been dropped on Nagasaki.

The prospect for the human race is sombre beyond all precedent. Mankind are faced with a clear-cut alternative: either we shall all perish, or we shall have to acquire some slight degree of common sense. A great deal of new political thinking will be necessary if utter disaster is to be averted.

For the moment, fortunately, only the United States is in a position to manufacture atomic bombs. The immediate result must be a rapid end to the Japanese war, whether by surrender or by extermination. The power of the United States in international affairs is, for the time being, immeasurably increased; a month ago, Russia and the United States seemed about equal in warlike strength, but now this is no longer the case. This situation, however, will not last long, for it must be assumed that before long Russia and the British Empire will set to work to make these bombs for themselves. Uranium has suddenly become the most precious of raw materials, and nations will probably fight for it as hitherto they have fought for oil. In the next war, if atomic bombs are used on both sides, it is to be expected that all large cities will be completely wiped out; so will all scientific laboratories and all governmental centres. Communications will be disrupted, and the world will be reduced to a number of small independent agricultural communities living on local produce, as they did in the Dark Ages. But presumably none of them will have either the resources or the skill for the manufacture of atomic bombs.

There is another and a better possibility, if men have the wisdom to make use of the few years during which it will remain open to them. Either war or civilization must end, and if it is to be war that ends, there must be an international authority with the sole power to make the new bombs. All supplies of uranium must be placed under the control of the international authority, which shall have the right to safeguard the ore by armed forces. As soon as such an authority has been created, all existing atomic bombs, and all plants for their manufacture, must be handed over. And of course the international authority must have sufficient armed forces to protect whatever has been handed over to it. If this system were once established, the international authority would be irresistible, and wars would cease. At worst, there might be occasional brief revolts that would be easily quelled.

But I fear all this is Utopian. The United States will not consent to any pooling of armaments, and no more will Soviet Russia. Each will insist on retaining the means of exterminating the other, on the ground that the other is not to be trusted.

If America were more imperialistic there would be another possibility, less Utopian and less desirable, but still preferable to the total obliteration of civilized life. It would be possible for Americans to use their position of temporary superiority to insist upon disarmament, not only in Germany and Japan, but everywhere except in the United States, or at any rate in every country not prepared to enter into a close military alliance with the United States, involving compulsory sharing of military secrets. During the next few years, this policy could be enforced; if one or two wars were necessary, they would be brief, and would soon end in decisive American victory. In this way a new League of Nations could be formed under American leadership, and the peace of the world could be securely established. But I fear that respect for international justice will prevent Washington from adopting this policy.

In view of the reluctance of mankind to form voluntarily an effective international authority, we must hope, and perhaps we may expect, that after the next world war some one Power will emerge with such preponderant strength as to be able to establish a peaceful hegemony over the rest of the globe. The next war, unless it comes very soon, will endanger all civilized government; but if any civilized government survives and achieves supremacy, there will again be a possibility of ordered progress and the utilization of science for happiness rather than for destruction.

One is tempted to feel that Man is being punished, through the agency of his own evil passions, for impiety in inquiring too closely into the hidden secrets of nature. But such a feeling is unduly defeatist. Science is capable of conferring enormous boons: it can lighten labour, abolish poverty, and enormously diminish disease. But if science is to bring benefits instead of death, we must bring to bear upon social, and especially international, organization, intelligence of the same high order that has enabled us to discover the structure of the atom. To do this effectively we must free ourselves from the domination of ancient shibboleths, and think freely, fearlessly and rationally about the new and appalling problems with which the human race is confronted by its conquest of scientific power.

by Russell Bertrand, 1945

Dalam tulisan ini, kita akan mempelajari sejarah perkembangan teori atom, struktur atom, serta cara menuliskan distrubusi elektron dalam atom.

Teori atom pertama kali dicetuskan oleh John Dalton, seorang ilmuwan berkebangsaan Inggris, pada tahun 1808. Beliau menyatakan bahwa semua materi tersusun dari “building block” yang dikenal dengan istilah “atom”.  Teori atom Dalton dapat dirangkum dalam beberapa pernyataan berikut:

1. Semua unsur di alam tersusun dari partikel yang sangat kecil yang dikenal sebagai atom

2. Atom-atom suatu unsur adalah identik satu sama lainnya; atom suatu unsur berbeda dari atom unsur lainnya

3. Senyawa terbentuk dari atom-atom berbagai unsur; dalam pembentukan senyawa, perbandingan atom-atom unsur penyusun senyawa selalu merupakan bilangan bulat dan sederhana

4. Reaksi kimia merupakan peristiwa pemisahan, penggabungan, atau penataulangan (rearrangement) atom-atom; reaksi kimia tidak menciptakan atau memusnahkan atom

Seiiring dengan perkembangan zaman dan kemajuan teknologi, para ilmuwan mulai meneliti atom.  Pada tahun 1906, J.J. Thomson, seorang ilmuwan berkebangsaan Inggris, memperoleh Hadiah Nobel bidang Fisika atas keberhasilannya menemukan elektron, salah satu subpartikel penyusun atom. Beliau mengajukan model atom yang dikenal dengan istilah “model roti kismis”. Dalam teori ini, elektron dianggap tersebar secara acak pada permukaan atom berupa bola pejal bermuatan positif.

Pada awal abad ke-19, dua sifat atom telah jelas; di dalam atom terdapat sejumlah elektron dan atom bersifat netral. Untuk mempertahankan sifat netral tersebut, atom haruslah memiliki sejumlah muatan positif yang sama untuk menetralkan muatan negatif yang diemban elektron.  Pada tahun 1911, Ernest Rutherford, seorang ilmuwan berkebangsaan Selandia Baru, melakukan percobaan untuk mempelajari struktur atom dengan menggunakan sinar α yang ditembakkan pada lempengan emas. Beliau memperoleh hasil bahwa sebagian besar sinar  α akan diteruskan, sementara sebagian akan dibelokkan dan dipantulkan kembali. Oleh karena sinar α mengemban muatan positif, maka Beliau berkesimpulan bahwa sebagian besar ruang atom adalah kosong (hampa); atom memiliki muatan positif yang terkonsentrasi pada inti atom dengan densitas tinggi. Hasil penemuan Rutherford semakin melengkapi pengetahuan tentang struktur atom.  Muatan positif yang terdapat pada inti atom dikenal dengan istilah proton (oleh Goldstein).

Perkembangan selanjutnya telah menghasilkan temuan bahwa selain proton, di dalam inti atom terdapat sejumlah subpartikel yang memiliki massa yang hampir sama dengan proton, akan tetapi tidak mengemban muatan listrik. Hal ini dikemukakan oleh James Chadwick, ilmuwan berkebangsaan Inggris pada tahun 1932. Partikel tersebut kemudian dikenal dengan istilah neutron. Dengan demikian, atom bukanlah partikel terkecil penyusun materi; sebab, atom sendiri tersusun dari beberapa subpartikel yang lebih kecil, yaitu ELEKTRON, PROTON, dan NEUTRON.

Niels Bohr, seorang ilmuwan berkebangsaan Denmark, mengajukan model atom Bohr untuk melengkapi beberapa kekurangan dari teori-teori atom sebelumnya. Model atom Bohr menunjukkan bahwa elektron-elektron di dalam atom berada di dalam garis-garis lingkaran (orbit) dengan tingkat energi yang berbeda mengelilingi inti (pikirkanlah planet-planet yang sedang mengorbit mengelilingi matahari di dalam sistem tata surya). Bohr menggunakan istilah tingkat energi (kulit) untuk menggambarkan garis-garis lingkaran dengan level energi yang berbeda. Dengan demikian, struktur atom tersusun dari proton dan neutron pada inti atom yang dikelilingi oleh elektron pada kulit atom. Jumlah proton dalam inti atom sama dengan jumlah elektron pada kulit atom.

Elektron memiliki massa yang jauh lebih kecil bila dibandingkan dengan massa proton maupun neutron. Dengan demikian, massa atom, untuk keperluan praktis, dapat dianggap sebagai jumlah massa proton dan neutron (massa elektron yang sangat kecil dapat diabaikan).

Jumlah banyaknya proton ditambah dengan banyaknya neutron di dalam atom dikenal dengan istilah nomor massa (A).  Sementara, jumlah proton di dalam inti atom sering disebut dengan nomor atom (Z). Oleh karena atom bersifat netral, maka jumlah elektron yang dimiliki akan sama dengan jumlah proton. Simbol suatu unsur tertentu dapat dilengkapi dengan A dan Z, seperti yang dinyatakan dalam bentuk penulisan berikut:

_ZX^A

Berdasarkan jumlah proton, elektron, dan neutron yang dimiliki masing-masing unsur, maka unsur-unsur tersebut  dapat dikelompokkan ke dalam beberapa kategori berikut:

1. Isotop : unsur-unsur dengan nomor atom (Z) sama, tetapi nomor massa (A) berbeda

Contoh :  ₁H¹ (hidrogen), ₁H² (deuterium), dan ₁H³ (tritium)

2. Isobar : unsur-unsur dengan nomor massa (A) sama, tetapi nomor atom (Z) berbeda

Contoh : ₁₅P³² dan ₁₆S³²

3. Isoton : unsur-unsur dengan jumlah neutron sama (A-Z, sama)(dibaca: A kurang Z, sama)

Contoh : ₇N¹⁴ dan ₈O¹⁵

4. Isoelektron : unsur-unsur dengan jumlah elektron sama

Contoh : ₉F^-, ₁₀Ne, dan ₁₁Na⁺

Atom yang bermuatan listrik netral dapat mengemban muatan positif maupun negatif apabila terjadi pelepasan atau penangkapan elektron (ingat: inti atom tidak boleh  mengalami perubahan; sebab, bila terjadi perubahan inti atom, sifat dan jenis unsur akan berubah pula). Atom atau kumpulan atom yang mengemban muatan listrik dikenal dengan sebutan ion. Ion yang mengemban muatan positif (terjadi saat atom kehilangan elektron) disebut kation; sementara ion yang mengemban muatan negatif (terjadi saat atom mendapatkan elektron tambahan dari luar) dikenal dengan istilah anion.

Berdasarkan model atom Bohr, elektron yang terletak pada kulit atom memiliki distribusi sedemikan rupa untuk mempertahankan baik posisi elektron di kulit atom maupun proton dan neutron (dikenal dengan istilah nukleon) pada inti atom. Susunan atau distribusi elektron di dalam kulit atom dikenal dengan istilah konfigurasi elektron. Berdasarkan model atom Bohr, elektron mulai mengisi pada kulit yang paling mendekati inti atom. Setelah dipenuhi, elektron akan mengisi pada kulit berikutnya, dan seterusnya, sesuai dengan jumlah elektron yang dimilikinya.

Kulit atom suatu atom dilambangkan dengan n. Kulit pertama atom memiliki nilai n=1. Sementara kulit kedua memiliki harga n=2, dan seterusnya. Masing-masing kulit memiliki nama dan kapasitas tertentu dalam menampung elektron.

n=1 dikenal dengan nama kulit K; menampung maksimum 2 elektron

n=2 dikenal dengan nama kulit L; menampung maksimum 8 elektron

n=3 dikenal dengan nama kulit M; menampung maksimum 18 elektron

n=4 dikenal dengan nama kulit N; menampung maksimum 32 elektron

Jumlah maksimum elektron pada kulit ke-n dapat ditentukan melalui persamaan 2n². Pengisian elektron hanya akan dilakukan pada kulit ke-n apabila kulit-kulit sebelumnya telah terisi penuh oleh elektron sesuai aturan 2n².

Berikut beberapa contoh penulisan konfigurasi elektron, baik atom maupun ion:

₆C : 2.4

₆C^4- : 2.8 (menerima 4 elektron tambahan pada kulit terluar)

₁₂Mg : 2.8.2

₁₂Mg²⁺ : 2.8 (melepaskan 2 elektron dari kulit terluar)

₁₇Cl : 2.8.7

₁₇Cl^- : 2.8.8 (menerima 1 elektron tambahan pada kulit terluar)

₂₀Ca : 2.8.8.2

₂₀Ca²⁺ : 2.8.8 (melepaskan 2 elektron dari kulit terluar)

₅₅Cs : 2.8.18.18.8.1

₅₅Cs⁺ : 2.8.18.18.8 (melepaskan 1 elektron dari kulit terluar)

Pelepasan maupun penangkapan elektron dapat mengubah jumlah elektron pada kulit terluar (dikenal dengan istilah elektron valensi). Unsur-unsur yang memiliki elektron valensi sama, umumnya memiliki sifat kimia yang serupa, dan dikelompokkan dalam satu kolom (dikenal dengan istilah golongan). Sementara unsur-unsur yang memiliki jumlah kulit terisi elektron sama, umumnya memiliki sifat yang bervariasi dan mereka dikelompokkan dalam satu baris (dikenal dengan istilah periode). Dengan demikian, konfigurasi elektron telah mempermudah ahli kimia dalam mempelajari sifat unsur-unsur dan mengelompokkan serta menyusunnya dalam tabel periodik (tabel berkala) unsur.

Unsur-unsur di alam umumnya terdapat dalam bentuk senyawa. Hanya beberapa unsur yang terdapat dalam keadaan bebas di alam. Salah satunya adalah golongan gas mulia VIIIA. Unsur-unsur dalam golongan VIIIA tidak berikatan dengan unsur lainnya karena telah mencapai kestabilan. Kestabilan gas mulia diperoleh karena semua kulit terisi penuh oleh elektron dan elektron valensi gas mulia selalu 8 (kecuali Helium yang hanya memiliki elektron valensi 2). Dengan demikian, unsur-unsur cenderung berikatan satu sama lainnya dengan tujuan untuk meniru konfigurasi elektron gas mulia yang terdekat (memiliki 8 elektron valensi), baik melalui cara serah-terima elektron maupun pemakaian bersama pasangan elektron (pembahasan lebih lengkap bisa dilihat pada bab Ikatan Kimia).

Golongan IA (Alkali) cenderung melepaskan 1 elektron membentuk ion dengan muatan +1

Golongan IIA (Alkali Tanah) cenderung melepaskan 2 elektron membentuk ion dengan muatan +2

Golongan IIIA (Boron-Aluminium) cenderung melepaskan 3 elektron membentuk ion dengan muatan +3

Golongan IVA (Karbon) cenderung melepaskan 4 elektron membentuk ion dengan muatan +4 atau menerima 4 elektron membentuk ion dengan muatan -4

Golongan VA (Nitrogen-Fosfor) cenderung menerima 3 elektron membentuk ion dengan muatan -3

Golongan VIA (Oksigen-Belerang) cenderung menerima 2 elektron membentuk ion dengan muatan -2

Golongan VIIA (Halogen) cenderung menerima 1 elektron membentuk ion dengan muatan -1

Golongan VIIIA (Gas Mulia) telah mencapai kestabilan dengan 8 elektron valensi sehingga tidak membentuk ion

Referensi:

Andy. 2009. Pre-College Chemistry.

Chang, Raymond. 2007. Chemistry Ninth Edition. New York: Mc Graw Hill.

Moore, John T. 2003. Kimia For Dummies. Indonesia:Pakar Raya.

Advance 2008

by Stephen bohr

1. Defending The Sabbath
2. Defending The Second Coming
3. Defending The Spirit of Prophecy
4. Defending The State of The Dead

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