Topic 1: Atoms and the Periodic Table

The radius of an atom

About 0.1 nanometres (1 x 10^-10 m).

The radius of a nucleus compared to the atom

The nucleus is less than 1/10,000 of the radius of an atom.

Charge and Mass of a Proton

Mass = 1, Charge = +1.

Charge and Mass of a Neutron

Mass = 1, Charge = 0.

Charge and Mass of an Electron

Mass = Very small (1/2000), Charge = -1.

Why do atoms have no overall electrical charge?

The number of protons (+ve) equals the number of electrons (-ve), so they cancel out.

Atomic Number

The number of protons in an atom.

Mass Number

The total number of protons and neutrons in an atom.

Definition of an Element

A substance made of only one type of atom (all atoms have the same number of protons).

Definition of an Isotope

Atoms of the same element with the same number of protons but different numbers of neutrons.

Relative Atomic Mass (Ar)

The average mass of all the isotopes of an element, weighted by their abundance.

Definition of a Compound

Two or more elements chemically combined in fixed proportions.

Standard shell rules for electrons

2, 8, 8 (filling from the lowest energy level/innermost shell first).

Group Number link to electrons

The Group Number tells you how many electrons are in the outer shell.

Period Number link to electrons

The Period Number tells you how many shells the atom has.

Plum Pudding Model description

A ball of positive charge with negative electrons embedded in it.

Alpha Particle Scattering Experiment: Observation 1

Most alpha particles passed straight through (proving the atom is mostly empty space).

Alpha Particle Scattering Experiment: Observation 2

Some particles were deflected (proving the mass is concentrated in a tiny, positive nucleus).

Niels Bohr's contribution

Suggested that electrons orbit the nucleus at specific distances (energy levels/shells).

James Chadwick's contribution

Provided evidence for the existence of neutrons within the nucleus.

Newlands' Octaves flaw

He assumed all elements had been discovered and forced them into a strict pattern of 8.

Mendeleev: Why he left gaps

For elements he predicted had not been discovered yet.

Mendeleev: Why he swapped order

He changed the order of some elements so their properties matched the group, ignoring atomic mass.

Modern Periodic Table arrangement

Arranged by increasing Atomic Number (number of protons).

Metals: Position and Ion formation

Found on the left/bottom; they lose electrons to form positive ions.

Non-metals: Position and Ion formation

Found on the right/top; they gain electrons to form negative ions.

Group 0 (Noble Gases) properties

Unreactive (inert) because they have a stable, full outer shell of electrons.

Group 0 boiling point trend

Boiling points increase as you go down the group (due to increasing atomic mass).