Chemistry: Intro to Atomic Theory

JJ Thompson

- Plum pudding model
- Electrons embedded in a sphere of positive charge

Lord Rutherford

- Gold foil experiment: Shot alpha particles at gold leaf, most passed through, some deflected at large angles
- Proved that most of an atom is empty space, there are a few particles floating around/in fixed positions
- Positive nucleus, orbiting electrons

Current Atomic Model

- Protons and neutrons in a nucleus
- Electrons orbiting in shells around the nucleus

Mass of Subatomic Particles (in comparison to proton): Protons, Neutrons, Electrons

Protons: 1
Neutrons: 1
Electrons: 1/1800

Atomic Number

Number of Protons in an atom (usually same number of electrons too to balance the charge)

Mass Number

Number of Protons + Number of Neutrons

Isotopes

- Atoms of the same element that have different numbers of neutrons, and therefore, different atomic mass
- Eg: Isotopes of Carbon: Carbon-13, Carbon-14

Periodic Table

G1: Alkali Metals
G2: Alkaline Earth metals
G17: Halogens
G18: Noble gases
Staircase between: Metalloids
Everything left of the staircase: Metals
Group in between: Transition metals
Everything right of the staircase: Non metals

Properties of Metals

- Lustrous
- Good conductors of heat and electricity
- Dense
- Solid at room temperature
- Malleable
- Ductile

Properties of Non Metals

- Can't be a solid, liquid or gas at room temperature
- Don't conduct electricity or heat
- Dull
- Brittle

Properties of Metalloids

Have properties of both metals and non metals

Core Charge

- The attraction from the nucleus felt by the valence electrons.

- Total number of electrons = Total number of protons

- Positive charge needs to get to valence electron by passing through all inner shell electrons

- Protons - inner shell electrons = + or - core charge

Atomic Radii

- Atomic radii is the distance from the centre of the nucleus to the valence shell.

- As core charge increases across a period, so does the force of attraction, bringing valence electrons closer to the nucleus, compacting the atom and decreasing atomic radii.

- Similarly as core charge decreases across a group, the atomic radii increases as the force of attraction is weaker.