1. Chapter 3- Atomic Structure
Atomic Theory
Chapter 3- Atomic Structure

2. John Dalton
Transformed ideas from Democritus , Lavoisier and others into a scientific Theory named:
Dalton’s Atomic Theory

3. Dalton’s atomic theory
1) all matter is made of atoms. Atoms are indivisible and indestructible
UPDATE: Atoms are made of smaller parts
2) All atoms of a given element are identical in mass and properties
UPDATE: Atoms have isotopes and are not all alike
3) Compounds are formed by a combination of 2 or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms
These points are based upon the Law of Conservation of Mass and the Law of Definite Proportions.

4. J. J. Thomson
Used Cathode ray experiments to discover the negative material within the atom.
He called these particles ELECTRONS.

5. Cathode Ray Tube:
The cathode ray experiment consisted of a cathode tube filled with a gas.
As electricity flowed through the tube, the gas showed up as a glowing beam.
When magnets were placed on the tube, the negative plates deflected the beam
Thomson proposed that the gas contained negative particle and he called his model of the atom the PLUM PUDDING MODEL
Plum Pudding

6. Robert Millikan
Carried out his OIL DROP experiment to determine the charge mass ratio of the electron.

7. Ernest Rutherford
Used alpha particles and gold foil to discover the nucleus of the atom.

8. The Gold Foil Experiment
Rutherford set out to test Thomson’s Model.
He aimed ALPHA particles (positively charged Helium atoms) at a thin sheet of gold.

9. Rutherford’s Atom
According to Thomson’s Model, the alpha particles should pass straight through.
Most particles passed through but some bounced back. WHY?

10. The Nucleus
In order for large positive particles to be deflected they had to hit a positive particle.
Rutherford theorized that the atom is mostly empty space with a positive dense center—the NUCLEUS
electron
Nucleus

11. James Chadwick
Confirmed the existence of the neutron, a particle with no charge but contributes to the mass of the atom.

12. Neils Bohr
Proposed that an electron is found only in specific circular paths or ORBITS around the nucleus

13. The Bohr model Within the atom electrons move in ORBITS
The first orbit holds 2 electrons
The second orbit holds 8 electrons
The third level holds 18 electrons

14. Movement of electrons
Ground state: the orbit containing the lowest energy for an electron
Excited state: the orbit of higher energy for an electron.
A ground state electron absorbs energy to move to the excited state.
There must be a specific amount of energy (QUANTA)applied to move the electron