9.3 Chemical periodicity of other elements

The characteristic properties of an element arise from its electron configuration, bonding model and the structures it forms. Position in the periodic table is a starting clue, not a complete explanation.

Use effective nuclear charge and shell structure for atomic trends; use lattice, molecular or metallic models for bulk properties.

A Group 2 metal conducts because of delocalised electrons, while a molecular Group 17 element has weak intermolecular forces and a low boiling point.

Do not mix atomic trends with compound trends. A metal’s atomic radius and its oxide’s acidity are related through different levels of explanation.

An unknown element can be located by combining periodic-table position clues with measured properties such as ionisation energy, atomic radius, bonding or reactions.

First identify the likely group/period from the strongest evidence, then check whether the proposed element’s structure and reactions fit. Do not force one measurement to decide everything.

A large jump after two successive ionisation energies suggests two valence electrons; if the element also forms a basic oxide and conducts as a solid, a Group 2 metal is plausible.

A single property is rarely unique. Use multiple independent clues and state what each one supports or rules out.