1. 4.1 Studying Atoms
Democritus (ancient Greek thinker)- atom indivisible and indestructible; 1st, not based on sci method
2000yrs pass
Dalton’s Atomic Theory
Elements made of particles, atoms of same element identical, atoms of different elements combine chemically in whole # ratios, chem rxn when joined/separated/re-arranged (not changed into another atom)
Size: radii most atoms 5x to 2x m

2. 4.1 Studying Atoms Thomson’s Model Charged particles in pressure tube
Provides first evidence that atoms are made of subatomic particles
Speed of e-/ angle of deflection/ strength of currents

3. 4.1 Studying Atoms
Rutherford’s Gold-Foil Exp-alpha particles (He atoms lost e-) being double + charge should pass thru gold foil easily, most did pass straight but some bounced off at large angles and some bounced straight back!
Rutherford Atomic Model (aka nuclear atom)-atom is mostly empty space, + charge and mass is concentrated in nucleus (very small)

4. 4.2 Structure of the Atom
Electrons (e-)-Thomson (plum-pudding e- stuck in + charge) exp passing electric current thru gas at low pressure resulted in cathode ray (glowing beam) from cathode (-end) to anode (+end)
Protons (p+)-Goldstein exp showed canal rays/ positive particles, mass p+ 1840x that of e-
Neutrons (neutral)-Chadwick discovered

5. 4.2 Structure of the Atom Atomic Number- # p+
Mass Number- #p+ and neutrons
# neutrons= mass # - atomic #
Isotopes- diff # neutrons (diff mass #’s!!)
Atomic Mass Unit (amu)-1/12 of mass of 1 carbon-12 atom
Atomic Mass- weighted avg atomic mass naturally occurring
Periodic Table
Period: rows, pattern of properties as move across
Group: columns, have similar chem/phys properties (family)

6. 4.3 Modern Atomic Theory Atomic orbitals e- cloud
e- orbital levels, move when gains/ loses E
Arrangement of e- is electron configuration
Most stable/ lowest possible E level is called ground state
e- cloud
Approximation of where e- are located around nucleus