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Chemistry Unit 1 Cheat Sheet by

Scientists and their discoveries for understanding the atomic theory

Empedocles (500 B.C)

All matter is made up of water, earth, air & fire

Democritus (300 B.C)

Known as The Laughing Philos­opher
Atoms are indi­vis­ible, inde­str­uct­ible, in motion & differs in shapes and sizes

John Dalton (Early 1800s)

Billiard Ball Model / Solid Sphere Model
Atoms can't be dest­roy­ed, subd­ivi­ded or crea­ted
Atoms of the same element have iden­tical proper­ties; Atoms from different elements have diff­erent proper­ties
During chemical reactions, atoms can be rear­ran­ged, sepa­rated or crea­ted
Atoms are combined in simple whole number ratios

J.J Thompson (Late 1800s)

Plum Pudding Model
Discovered that elec­trons are stuck in a posi­tively charged matter
Conducted the cath­ode-ray experi­ment; Beta particles were attracted to the positively charged magnets

Ernest Rutherford (1911)

Nuclear Model / Ruther­ford's Model
Dense, tiny positively charge in the centre of an atom
Several spaces in an atom
Most of the mass is in the nucleus
If J.J Thompson's discovery was accurate, the particles would've had minor deflec­ts, but there were major deflects
Gold foil was used b/c it is the most mall­eable metal

Niels Bohr (1913)

Planetary Model / Bohr's Model
Electrons emit phot­ons (quantum of light) jumps up or down to other shells and doesn't spiral into the nucleus while emitting phot­ons

Max Planck

Proposed that particles can emit a certain amount of elec­tro­mag­netic radiat­ion
Electrons need to obtain the amount of energy before emitting it
Analogy: Similar to a bank machin­ can only receive multiple of $20.00, although other amounts exit (e.g. $32.00)

Werner Heisen­berg's Uncert­ainty Principle

It's impossible to know both the posi­tion (location) & the mome­ntum (speed) of a particle at any given moment

Erwin Schrod­inger (1926)

Quantum Mechanical Model
Mathem­ati­cally predicted the regions of space where electrons can be found

De Broglie

Quantum Mechanical Model
Electrons behave like waves & part­icles


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