1. Warm-Up
Draw a picture of an atom. Be as specific as you can!

2. History of the Atom

3. Democritus (400 B.C.) Greek philosopher
Coined the word atom, meaning indestructible
Atoms are solid, homogeneous, and indivisible
Different types of matter existed due to changes in the atoms that composed them
Problem: what holds the atom together?

4. John Dalton (19th century)
English schoolteacher
Modern Atomic Theory:
All matter is composed of atoms
All atoms of the same element have identical size, mass & chemical properties
Different atoms combine in specific ratios to form compounds
In chemical reactions, atoms are separated, combined or rearranged

5. Law of Multiple Proportions
2 H2 + O2  2 H2O
H2 + O2  2 H2O2

6. Cathode Ray Tube

7. Sir William Crookes (1800s)
Experimented with the CRD:
No charged objects  ray is straight and flows from cathode to anode
Positive charge near the tube  ray is deflected toward the charge
Negative charge near the tube  ray is deflected away from the charge
Conclusion: particles must be negatively charged

8. J.J. Thomson (1890s) English physicist
Used CRT to determine charge-to- mass ratio of the electron
Mass was much lighter than Hydrogen, the lightest atom
Conclusion: Atoms must be divisible!

9. Plum Pudding Model
Negative electrons evenly distributed throughout a uniform positive charge
“Chocolate chip cookie model”

10. Robert Millikan (1909)
American physicist (who shares a birthday with Ms. Breeze!)
Determined charge & mass of an electron:
Charge = 1-
Mass = 9.1 x g = 𝟏 𝟏𝟖𝟒𝟎 mass of H atom

11. Ernest Rutherford (1911) Gold Foil Experiment
Prediction: particles would pass straight through (almost)
Results: a few particles were deflected at large angles, some even straight back towards the source!

12. Nuclear Atomic Model Atom is made of mostly empty space
Electrons move through this
Tiny, dense region in the center called the nucleus
Positively charged
Almost all of the atom’s mass

13. James Chadwick (1932) English physicist
Nucleus also contains neutrons:
Neutral (no charge)
Same mass as a proton

14. Relative Electrical Charge
Subatomic Particles
Particle
Symbol
Location
Relative Electrical Charge
Relative Mass
Actual Mass (g)

15. Relative Electrical Charge
Subatomic Particles
Particle
Symbol
Location
Relative Electrical Charge
Relative Mass
Actual Mass (g)
Proton p+
In the nucleus +1 1
1.673x10-24
Neutron n0
Electron e-
In the space surrounding the nucleus -1
1/1840
9.11x10-28

16. Information found on the Periodic Table6 C
Carbon
12.011
Atomic Number = number of protons
Element’s Symbol
Element’s Name
Atomic Mass = protons + neutrons
In elemental forms, the number of protons will be the same as the number of electrons.
Carbon has 6 protons, 6 electrons, and an average of 6 neutrons.