1. The Atomic Theory

2. Democritus proposed the atom 440 BCE
Believed all matter was made of atoms
called this particle the atom (atomos which means not able to divide).

3. The Father of the Atomic Theory
John Dalton viewed the atom as a solid ball.
Proposed in 1803
All things are made of atoms and cannot be divided
Atoms of same element are alike and atoms of different elements are different
Atoms can join with others to make new things

4. Improving the Modern Theory
J.J. Thomson proposed the Plum-Pudding Model (named after is favorite dessert)
the atom has positively and negatively charged particles evenly distributed throughout the atom
discovered the electrons in 1897

5. Improving the Modern Theory
Ernest Rutherford discovered the atom was made of mostly empty space with a dense, positively charged center surrounded by electrons-1909
Called this center the nucleus and the positive particles in the nucleus he called protons.
Former student of J.J. Thomson

6. Improving the Modern Theory
Niels Bohr suggested electrons move in distinct, circular patterns known as energy levels
eˉ could jump from one energy level to another but not in between
Model known as Bohr’s Model

7. More Improvements
Schrödinger and Heisenberg: found that eˉ did not have a definite path but
Are unpredictable and found in a region called the electron cloud surrounding the nucleus

8. Finding the Neutron
James Chadwick discovered that the center of the atom contained another particle that carried no charge and had a mass close to a proton -1932
He called this particle the neutron.