Structure 3: Classification of Matter

Define a group

A vertical column in the periodic table; elements have the same number of valence electrons

Define a period

A horizontal row in the periodic table, elements have the same highest energy electron shell

State the general trend in atomic radius across a period

Atomic radius decreases across a period due to increasing nuclear charge and constant shielding

State the general trend in atomic radius down a group

Atomic radius increases down a group due to increasing number of electron shells

Define first ionization energy

Energy required to remove one mole of electrons from one mole of gaseous atoms

Trend in ionization energy across a period

Generally increases across a period due to higher nuclear charge and smaller atomic radius

Trend in ionization energy down a group

Generally decreases down a group due to increased distance from nucleus and electron shielding

Define electronegativity

The ability of an atom to attract shared electrons in a covalent bond

Electronegativity trend across a period and down a group

Increases across a period, decreases down a group

Trend in melting points across a period (general)

Increases for metals, peaks at giant covalent structures (Si) then decreases for nonmetals

Trend in electrical conductivity across a period

Metals conduct well, nonmetals poorly, semiconductors in between

Oxide types across a period

Metallic oxides - basic; nonmetallic oxides - acidic some intermediate oxides - amphoteric

Define transition metal

An element that forms at least one stable ion with a partially filled d subshell

Give common properties of transition metals

Variable oxidation states, form coloured compounds, act as catalysts, form complex ions

Why do transition metals have variable oxidation states?

Because both 3d and 4s electrons can be lost during bonding

What is a ligand?

An ion or molecule that donates a lone pair to a central metal atom to form a coordinate bond

What is a complex ion?

A central metal ion bonded to ligands via coordinate bonds

How does ligand field theory explain colour?

Ligands split the d orbitals of the metal ion into different energy levels and absorption of light promotes an electron from a lower to higher d orbital, producing colour