1. Introduction to Atoms – Chapter 11
Section 1 – Development of the Atomic Theory pp

2. DEFINITIONS
Atom – the smallest particle into which an element can be divided and still be the same substance.

3. DEFINITIONS
Nucleus - the tiny, very dense, positively charged region in the center of an atom. The nucleus is made up of protons and neutrons.

4. DEMOCRITUS Said that the atom is Indivisible
All atoms are small, hard particles made of a single material formed into different shapes and sizes
Atoms are always moving

5. DALTON’S MODEL OF THE ATOM
All substances are made of atoms.
Atoms of the same element are exactly alike; atoms of different elements are different.
Atoms join with other atoms to make new substances.

6. J.J. THOMSON MODEL
British scientist who discovered there are small particles inside an atom
Discovered negatively charged particles called electrons
This model is the first of many models to explain the structure of the atom

7. RUTHERFORD MODEL
Discovered positively charged particles in an atom called protons
Determined that the atom was mostly empty space with a dense center.

8. BOHR MODEL
Electrons travel around the nucleus of the atom in different paths

9. MODERN THEORY
Schrödinger and Heisenberg said that electrons do not travel in definite paths.
There are regions inside the atom where electrons are likely to be, these regions are called electron clouds.
Dense center with electrons outside the nucleus)