1. Origin of the idea of atom…
GREECE
Democritus ( b.c.): matter is made of tiny particles atomos

2. John Dalton’s Atomic Theory- 1803
Five notions about atoms… 1. All matter is made of atoms 2. All atoms of given element are identical 3. The atoms of one element are different from other elements 4. Atoms combine in whole ratios to make compounds: LAW OF CONSTANT COMPOSITION 5. In chemical reactions atoms are separated, combined, or rearranged. (but cannot be destroyed)

3. Atomic Structure Atoms are composed of 3 subatomic particles-
Electron- J.J. Thompson and Millikan
Proton- Goldstein and Rutherford
Neutron- Rutherford, Bohr

4. Electrons: J.J. Thomson- 1856-1940
Using a cathode ray tube he found that atoms emit tiny negative particles “corpuscle”
Found that atoms have particles that move AWAY from the negative end, so they must have a negative charge!

5. Protons- J.J.Thompson-1897 “Plum Pudding” Model
Electrons have a negative (-) charge
But atoms are neutral (no charge)
Therefore there must be a positive (+) charge too!

6. Protons- Ernest Rutherford - 1911
He shot (+) charged alpha particles at gold foil

7. Protons- Ernest Rutherford - 1911
Only a few positive particles were repelled
This disproved his hypothesis
There must be a VERY small positive central core (nucleus) , and the rest of the atom % is empty space.

8. Bohr model 1915 Protons and Neutrons are in the nucleus
Electrons are outside the nucleus in orbitals
Electrons can move from one orbital to another, and release energy as electromagnetic radiation.

9. Electron cloud Model
Electrons are in clouds (Schrodinger)

10. 3 subatomic particles 1.007 1.009 -1 5.486x10-4
Name
(symbol)
Charge
Mass (amu)
(atomic mass unit)
Actual Mass
location
Proton
(p) +1
1.007
1.673x10-24 g
Nucleus
Neutron
(n)
1.009
1.675x10-24 g
Electron
(e-) -1
5.486x10-4
(so small that its not counted!)
9.109 x10-28g
Outside Nucleus

11. Activity:
As scientists gained more evidence, their THEORIES on atoms changed… Analyze each of the following models with your partner

12. History of Atomic TheoriesaY

13. What makes one atom different from another?
The number of protons!
A difference in number of protons changes the actual element
You can change the number of electrons and neutrons and still have the same type of element

14. Reading the Periodic Table

15. How do we know how many subatomic particles are in each element?
Protons – Look at the atomic number!
Electrons – Atoms are neutrally charged, so the number of protons = number of electrons

16. How do we know how many subatomic particles are in each element?
Neutrons – The mass of the atom is made up of protons and neutrons
# neutrons = mass number – atomic number
Mass number is not the same as atomic mass, it is rounded to a whole number!

17. Element Coding: