quantum

 =The Quantum Mechanical Model of the Atom=

This wiki contains information about the Quantum Mechanical Model of the atom as it is being covered in the Ancaster High School Biotechnology IDP 4U1 course. The wiki is being used as a reference for Biotech students and as a complement to their in-class notes.

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Key Scientific Contributors Comparison of the Old and New Model Representing the Atom Key Concepts in Quantum



Key Scientific Contributors
//**J.J. Thomson**// - Had the plum pudding model of the atom. He worked with electrons to develop a model of the atom. This model became known as the "plum pudding" model. In the model, he described electrons as negative plums embedded in a pudding of positive stuff.


 * //Ernest Rutherford//** - conducted the gold foil experiment. He fired alpha particles at a thin gold foil. This was to prove if the cookie model by JJ Thompson was correct, if particles travel in a straight line them the particles should travel right through the atom in a straight line. However, when he fired the particles he found that they bounced off in different directions sometimes even deflecting backwards. This disproved Thompson's theory


 * //Max Planck//** - describes particles as being able to emit certain amounts of electromagnetic radiation. Realized that as an object heats up, it emits packets of energy called quanta. As quanta is emitted by electrons, their energy is lost and they return to their original amount of energy. He found that there had to be a reason why electrons stay in a set orbit, which disagrees with Rutherford's model of the atom.

//**Niels Bohr-**// explains the fact of why electrons don't spiral into the nucleus of the atom. He states that electrons orbit in specific locations based on their energy. This energy he explains occurs in "discrete packages" which means that it is quantized and every electron has its own amount of quantized energy. In addition the only way for these electrons to move orbits is for them to gain or lose their amounts of quantized energy. Bohr proved these theories using the hydrogen atom and through mathematics supporting these conclusions. Click [|here] for more information on Bohr's model of the hydrogen atom and the mathematical formula that was developed to predict the wavelengths of hydrogen spectrum.

//**Albert Einstein**//- While studying the photoelectric effect (look under key experiments for more details) he found that light acts as a particle. Einstein termed set amounts of light energy "photons". He discovered that once electrons absorb enough energy all at once (not summative), photons (different quanta of light) can be released/ejected by the electron.

//**Louis De Broglie**//- Founded the theory of Wave Particle Duality which explains: when traveling light acts as a wave, but once an object interferes it acts as a particle. De Broglie creates the wave-function mathematical formula which helps describe the nature of energy.

[|Timeline] This link gives extra info on these physicists and a timeline for the discoveries.

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Comparison of the Old and New Model
Old model has electrons arranged in cicular orbits around the nucleus. The new model has electrons in orbitals because the electrons are waves as they move around the nucleus. Orbitals are regions of space where electrons are most likely going to be. Orbitals have different energy levaels and shapes. In the new model electrons have a "spin", and electrons in the same orbital cannot have the same spin. In the old model electrons don't have a "spin", but instead orbit the nucleus in the same direction like a solar system. A similarity between the two models is that the different orbits in the old model have different energy levels, like how the different orbitals have different energy levels in the new model.

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Key Experiments and Concepts
//**Double Slit Experiment- The double slit experiment illustrates the wave- particle duality characteristic of light. Essentially, wave-particle duality means that when light is in motion, it travels as a wave and when this light energy is stopped (comes in contact with an object), the wave collapses to act as a particle. In the double slit experiment, light is shone through a solid plate which has two slits in it and this light then strikes another plate which is set up behind the plate containing the double slit. As light is shone towards the double slit, it is travelling in a wave function and as these waves pass through the two slits in the plate, they create an interference pattern with one another. The crests and troughs of the waves superimpose over one another creating areas of supercrests and supertroughs, as well as areas where the crests and troughs have cancelled each other out. As these superimposed waves strike the second plate which is set up to reveal the light, a pattern of alternating light and dark regions is found. The visible regions are those of the supercrests and supertroughs whereas the dark areas are where the initial waves have been cancelled out by one another. These baffling results prove wave-particle duality of light. For an easy to understand video click [|here]. Further information about this experiment and quantam mechanics can be found [|here].**// //**Photoelectric Effect**//- Einstein shone light on metal resulting in electricity being generated and he found the light gave enough energy to an electron to leave their orbits and be ejected into space. He found that it wasn't light intensity but infact light frequency (i.e. colour) that dictated the number of electrons being ejected. Einstein called these set amount of energy "photons" This is an ALL OR NOTHING effect. ERGO, the photoelectric effect proves that electrons behave as particles. BUT there was still a problem, when he shone light through double slits he got a series of bands of light and dark!?? Therefore, Louis De Broglie came up with a mathematical formula known as the wave- particle duality which helps describe the wave nature of energy and that: WHEN TRAVELLING IT ACTS AS A WAVE, BUT WHEN AN OBJECT INTERFERES IT ACTS AS A PARTICLE.
 * www.daviddarling.info/ encyclopedia/L/light.html**

Erwin Schrödinger's cat teaches the clear conflict between matter in the macro and quantum world. The theoretical experiment is that we place a living cat in a metal box. Which contains a vial of hydrocyanic acid and a small amount of radioactive substance. If even a single atom of the substance decays it will trigger a mechanism which will break the vial containing the acid and kill the cat. The observer has no clue whether the substance decayed or didn't decay because they are not observing whats happening in the box. Since we don't what has happened to the cat it's both dead or alive according to quantum law in a superposition of states. If we open the box the superposition is lost and now we know whether the cat is dead or alive. Here the observation affects the outcome but then there is no single outcome unless it is observed. Superposition happens at the sub-atomic level in which one particle is seen to be in multiple locations simultaneously. [|Video] This shows the experiment for better understanding.
 * Schrödinger's //Cat//**

In the quantum world objects do not follow the similar rules to the macro world. This concept explains the characteristics of micro objects such as electrons and photons. It states that when an object alike those stated before is moving it moves as a wave and is not visible, but when it is stopped the wave collapses on itself and becomes a visible particle. This concept is still widely debated but is the major concept that can clearly explain the double slit experiment.
 * //Wave-Particle Duality//**

Developed by Werner Heisenburg, the Uncertainty Principle states that it is impossible to know the position and momentum (velocity) of a particle at any given moment. We can know velocity, but the act of finding location causes the wave to collapse back into a particle and we can find location, but we no longer can determine velocity.
 * The Uncertainty Principle**

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Representing Atoms with the Quantum Model
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