History of Chemistry

Democritus

discovered the idea of atoms.

Boyle

discovered the idea of simple elements (H, O, He)

Giorg Stahl

first person to explain the burning process (completely wrong, phlostogion)

Antoine Lavoisier

Combustion, Law of Conservation of mass

Proust

Law of constant composition (LCC/law of definite proportions)

John Dalton

School teacher interested in compounds, created law of multiple proportions.

Law of Multiple proportions

governs the ratio of compounds

JJ Thompson

cathode ray tube experiment, saw a beam, determined direction.

Cathode Ray tube experiment

Declared negative side cathode and positive side anode.

Concluded cathode ray must be made of smaller things.

Discovered idea of protons and electrons.

Bequerel

discovered radiation and their properties (alpha, beta, gamma)

Alpha α

Charge: 2+

Mass: 4u

Speed: Slow

Penetration: Low

Beta β

Charge: 1-

Mass: 1/1840u

Speed: high

Penetration: moderate

Gamma γ

Charge: 0

Mass: 0

Speed: c (3×10^8ms^-1)

Penetration: high

Rutherford

Gold foil experiment

Gold Foil Experiment

1) Atoms are 99.9999% empty space

2) There is a small positive charge causing deflection

3) There is a small dense positive center (nucleus)

Simple Average

Average of H=1

H 3, 2, 1=most abundant

Weighted Average

Mass of 1st Isotope*abundance + 2nd isotope*abundance

Uses a mass spectrometer to find %’s

Band of stability

pre-82 periodic table

Anything beyond band of stability can gain protons or lose electrons at the same time

Right before band= beta decay, ‘neutron rich”

Bohr

Light is quantized (photons)

Matter can absorb energy (quanta)

Wavelength big, frequency small

Radiowaves, microwaves, infared, x ray, gamma (longest to shortest)

Bohrs Model

Concluded an electron had a minimum energy

structure of the atom is quantized- certain amount of energy needed to move electron outward.