Atomic Models

Atomic Models

What does the unseen look like?

There have been many atomic models over the ages

• Billiard Ball - Dalton

• Tiny Real-Life - Democrats

• Plumb Pudding - Thomson

• Planetary - Rutherford

• Energy Level - Bohr

• Quantum - Schrodinger

Dalton

• Was the first modern scientist to propose the atomic theory.

• He thought that atoms were made of microscopic hard balls where every atom of an element had the same properties (for example: radius and mass)

Problems with Dalton's Model

• In experimentation with different gases scientists, most notably J.J. Thomson, discovered positive and negative charged particles in the gas.

• Dalton's Model didn't account for this

Thomson - Plum Pudding Model

In trying to explain the negative and positive charged particles in his experiments JJ Thomson developed the plum pudding model

Plum Pudding Model

After Thomson discovered electrons, in cathode ray tube experiments, he developed the model to explain the existence of positive and negative charged particles that had less mass than the atoms of the element

Plum Pudding Model

Thomson's proposed model consisted of electrons evenly spaced through out a positively charged atom. His model was similar to Dalton's in that it was still a solid structure.

Multiple Choice

Where did Thomson say the electrons were in the atom?

• Round the outside

• Evenly spaced throughout the positively charged atom

• At the center of the atom

Multiple Choice

What atomic particle did Thomson discover that he was trying to account for in his model?

• Proton

• Electron

• Neutron

• Graviton

Rutherford's Planetary Model

• In Rutherford's gold foil experiment he was testing Thomson's model (Fig A)

• He expected the particles he was shooting to go through the gold foil (top - fig B) with some deflection. Instead, it deflecting almost directly back at the source. (Bottom - Fig B).

Rutherford's Planetary Model

• Because of this Rutherford proposed the first model to have a positively charged nucleus with electrons orbiting. He proposed that the nucleus also contained most of the mass of the atom.

• Rutherford proposed that the electrons behaved like planets orbiting a star. His diagram is still used to represent atoms in commercial settings.

Rutherford's Planetary Model

• Many physicists distrusted the Rutherford atomic model because it was difficult to reconcile with the chemical behaviour of atoms.

Multiple Choice

What happened during Ruthafords gold foil experiment that made him develop a new model?

• All of the particles he was shooting at the gold foil went strait through.

• All of the particles he was shooting at the gold foil bounced back at the source.

• Most of the particles he was shooting at the gold foil passed through wil some deflection while a few came back towards the source

Multiple Choice

What was a new concept introduced in the Ruthafords model?

• That the positive charge orbited the outside of the atom

• That the positive charge was concentrated in the cent of the atom

• That electrons were bigger then protons.

Energy Level Model - Bohr

• Niels Bohr, a student of Rutherford, in trying to explain why hydrogen gas emits light when electricity passed through it explained on Rutherford's model

Energy Level Model - Bohr

• Bohr's model explained that the electrons didn't just orbit the nucleus but did so at specific energy levels.

• It was an electron changing energy levels that explained hydrogen emitting light

Energy Level Model - Bohr

• Fun fact 1: While today people expand on Bohr's model, to discuss atomic structure, he never built a model beyond hydrogen.

• Fun fact 2: Bohr's model is only partially correct according to our most modern atmoic models.

Multiple Choice

What was Bohr trying to figure out when he developed his atomic model with energy levels?

• Why electrons behaved like waves

• Why atoms consumed energy in reactions

• Why hydrogen produced light when electricity runs through it.

Quantum Model - Schrodinger

The Bohr model was unable to explain some behavior seen in atoms. For example, the fact that it seems like electrons behave like particles and waves at the same time.

Quantum Model - Schrodinger

Quantum theory was developed to explain these behaviors and a new model was developed.

Quantum Model - Schrodinger

The quantum model proposes that there is no way to know exactly where an electron will be or where it is going, eliminating the idea of electrons have exact orbits, so it is more of an electron cloud.

Quantum Model - Schrodinger

Schrodinger developed some equations that would predict, with a high degree of probability, the region of the electron cloud you could find an electron based on the energy level.

You can see those regions to the right. They are refered to as orbits.

Quantum Model

The Quantum Model is our current model of the atom.

Multiple Choice

Why is Schrodinger's model more like electron clouds than exact electron paths?

• Quantum Theory states that there is no way to know exactly where and electron is and where it is going

• Quantum Theory states that you can't put electrons in one place or they will collide with other atoms

• Quantum Theory states that there can only be 1 electron on an atom at a time.