6. HIROSHIMA 1945

7. 1.3: History and Particles
ATOMIC THEORY
Day 1
1.3: History and Particles

8. Changes in the Model of the Atom
Day 1

9. 1. DALTON
- everything is made of atoms - different elements combine to form compounds in simple whole ratios - each element has its own unique type of atom with a characteristic weight - small indivisible solid particle model

10. 2. THOMSON
- discovery of subatomic particle (electron) Cathode ray experiment - rays are particles, not waves - new particles are negative, lighter than smallest atom (hydrogen) - plum pudding model

11. 3. RUTHERFORD Thin gold foil experiment
alpha particles mostly pass through foil
but sometimes deflected back when they hit something massive
thus, atom made mostly of empty space
core of positively charged material, where most of the mass of the atom is (nucleus)
why don’t negative electrons give in to the pull of the positive nucleus and collapse inwards?

12. 4. BOHR
- negatively charged electrons found in concentric circular orbits around the positive charged nucleus - electrons found at fixed energy levels orbiting at fixed distances from the nucleus - path closest to nucleus = lowest energy level - energy higher the farther the orbits are from the nucleus - the farther the electron is from the nucleus, the less attraction it feels - electrons can jump from one energy level to another, but are not found between levels - they lose or gain a discrete package of energy (quantum of energy) every time it jumps levels  quantum leap - explains why each element has a certain number of electrons available for reactions - the electrons found on the outer most orbit  valence electrons - planetary model

13. The Kinetic Molecular Theory

16. Textbook: Page 32