Acidic oxide - oxide of non-metals

Actinide - the fifteen metallic elements with atomic numbers 89 to 103

Allotrope - two or more forms of the same element in which the atoms or molecules are arranged in different ways

Amphoteric oxide - oxide that being able to react as an acid or a base

Atomic radius - mean or typical distance from center of atom's nucleus to the boundary of the surrounding cloud of electrons

Basic oxide - oxide of metals

Covalent radius - half of the distance between two singly bonded atoms of the same element

Delocalized electron - the outermost shell electrons of each atom in a metal, which are not associated with a particular ion and can move around

Effective nuclear charge - net positive charge experienced by an electron in a multi-electron atom

Electrical conductivity - ability to conduct electricity

Giant covalent structure - In substances with giant covalent structures, millions or more atoms are held together by strong covalent bonds.

Giant metallic structure - the structure of a metal, in which ions are packed tightly together in a regular pattern to form a giant structure

Lanthanide - the fifteen metallic elements with atomic numbers 57 to 71

Main group element - the 8 groups of elements which are positioned in group I, II, III, IV, V, VI, VII and 0 in the periodic table

Metallic radius - half of the distance between the two adjacent metal ions in the metallic lattice

Periodicity - recurring trends in properties of elements in periodic table

Shielding effect - reduction in the effective nuclear charge on the electron cloud, due to a difference in the attraction forces with other electrons around the nucleus

Simple molecular structure - the structure of a substance in which strong covalent bonds hold the atoms in each molecule together while much weaker van der Waals’ forces hold the separate molecules

Transition metal - elements between Groups II and III of the periodic table

Van der Waals' forces - a weak attractive force between two atoms or non-polar molecules, which arises because a fluctuating dipole moment in one molecule induces another dipole moment in oth