1. ATOMS!

2. Early models of the atom The existence of the atom was first proposed by Democritus of Abdera who lived in Greece during the 4th century B.C. 2000 years after Democritus lived the modern process of discovery regarding atoms began with John Dalton. Dalton was able to test and correct his atomic theory through experiments.

3. John Dalton John Dalton Lived from 1766-1844. He was an English teacher. Dalton studied the ratios in which elements combine in chemical reactions. Dalton used the results of his experiments to formulate hypothses and theories to explain his observations. These led to Dalton’s atomic theory.

4. Dalton’s Atomic Theory 1. All elements are composed of tiny indivisible particles called atoms. 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element. 3. Atoms of different elements can physically mix together or can combine chemically in simple, whole number ratios to form compounds. 4. Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element cannot be changed into another element through a chemical reaction.

5. Facts... We now know that atoms are divisible! Atoms are so small that if you were to line up one billion copper atoms they would only measure one centimeter in length! Scientists use a scanning tunneling microscope to see the surfaces of atoms. There are dozens of subatomic particles!

6. Protons Have a positive charge Discovered by E. Goldstein in 1886 Has a mass 1840 times greater than that of an electron

7. Electrons Have a negative charge Discovered by J.J. Thomson in 1897 Carries exactly one unit of negative charge It’s mass is 1/1840 of a Hydrogen atom

8. Plum pudding model

9. How are atoms put together? In 1911 Earnest Rutherford and his colleagues tested the theory of atomic structure. Tested this by using the “Gold Foil Experiment” This led to the conclusion that an atom is mostly empty space and has a nucleus which is the central core of the atom and composed of protons and neutrons.

11. There are TWO regions of an atom… Nucleus -Most of the mass -Has a positive charge Electron Cloud -Most of volume/space -Has a negative charge

12. The 3 subatomic particles we will study are... Electrons Protons Neutrons Bohr Model

13. Neutrons Have no charge Discovered in 1932 by English Physicist, James Chadwick Mass approximately same as that of a proton

14. Modern Atomic Model