1. Cook

2.  At the end of the 19 th Century, scientists began to probe the submicroscopic world of atoms  Development of atomic models John Dalton: Thought the atom was to be considered to be a solid indestructable mass. He developed the Atomic Theory

3.  All atoms are composed of tiny indivisible particles called atoms  Atoms of the same element are identical. The atoms of any one element are different from those of any other atom  Atoms of different elements can combine with one another in simple whole number ratios  Chemical reactions occur when atoms are separated, joined or rearranged

4.  Discovered the electron using cathode ray experiment Electron e - 1 - 9.11x10 -23 Proton p + 1 + 1.67x10 -24 Neutron n + 0 1.67x10 -24 http://www-outreach.phy.cam.ac.uk/camphy/electron/electron4_1.htm This lead to the discovery of atomic models Plumb pudding model

5.  The discovery of the electron lead to many different models of the atom Plum Pudding model  Negatively charged electrons stuck in a lump of positively charged protons. Didn’t explain neutron Rutherford’s Model  Nuclear atom in which electrons surround a dense nucleus, and the rest of the atom is empty space Bohr’s Model  Electrons are arranged in concentric circular paths, sort of like the planets

6.  See Page 246  Be able to differentiate between the following: Thompson model Rutherford’s Model Bohr Model Quantum Mechanical Model

7.  Refer to Bohr’s model (it’s the most commonly accepted) All electrons have fixed energy They do not lose energy and fall into the nucleus  Energy Level:  Is the region around the nucleus where it is likely to be moving.  Like rungs on a ladder  Lowest rung has the lowest energy level  Energy levels increase as u move up the ladder

8.  The amount of energy gained or lost by every electron is not the same Unlike rungs on a ladder, the energy levels in an atom are not equally spaced  Quantum:  Is the amount of energy required to move an electron from it present energy level to the next

9.  Erwin Schrodinger took atomic models a step further He used the quantum theory to write and solve mechanical equations describing the location of the electron  Quantum Theory Quantum theory is the theoretical basis of modern physics that explains the nature and behavior of matter and energy on the atomic and subatomic level.

10.  A modern description of electrons in atoms. It is based on mathematical equations.