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Periodicity and Period 3 definitions

Every term the lessons in this unit define, lesson by lesson, worded as the lessons use them. Each lesson title links to its notes.

32 terms

Periodicity: trends across Period 3 and the blocks of the table

Periodicity: A repeating pattern of physical or chemical properties across the periods of the periodic table.
s-block element: An element whose last electron, in filling order, enters an s subshell, as in groups 1 and 2.
p-block element: An element whose last electron, in filling order, enters a p subshell, as in groups 3 to 0.
d-block element: An element whose last electron, in filling order, enters a d subshell, as from scandium to zinc.
Atomic radius: Half the distance between the nuclei of two bonded atoms of the same element.
Shielding: The repulsion of an outer electron by the electrons in inner shells, which reduces the attraction of the nucleus it feels.
First ionisation energy: The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
Metallic bonding: The electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons.
Giant covalent structure: A lattice in which every atom is joined to its neighbours by covalent bonds extending throughout the whole structure.
Van der Waals forces: Weak attractions between molecules caused by temporary dipoles, which induce dipoles in neighbouring molecules.
Ionic radius: The radius of an ion in an ionic lattice, found from the distance between the nuclei of neighbouring ions.
Isoelectronic: Describes atoms or ions that have the same number of electrons in the same electron configuration.

Alkali: A base that dissolves in water to release hydroxide ions, OH⁻(aq).
Oxidation: The loss of electrons by a species, or an increase in its oxidation state.
Reduction: The gain of electrons by a species, or a decrease in its oxidation state.
Oxide: A compound containing oxygen and one other element only.
Oxidation state: The charge an atom would have if all its bonds were ionic; the oxidation states in a neutral compound add up to zero.
Empirical formula: The simplest whole-number ratio of atoms of each element in a compound.
Molecular formula: The actual number of atoms of each element in one molecule of a compound.
Sublimation: The change of state of a substance directly from solid to gas, without melting.
Dimer: A molecule formed when two identical molecules join, as two AlCl₃ molecules join to form Al₂Cl₆.
Dative covalent bond: A covalent bond in which both electrons of the shared pair come from the same atom.

Ionic bonding: The electrostatic attraction between oppositely charged ions in a lattice.
Covalent character: Partial sharing of electrons in an ionic compound, caused by a small, highly charged cation distorting the electron cloud of the anion.
Basic oxide: An oxide that reacts with acids to form a salt and water; in Period 3, an ionic oxide containing O²⁻ ions.
Acidic oxide: An oxide that reacts with bases to form a salt and water; in Period 3, a covalent oxide.
Oxoacid: An acid in which the acidic hydrogen atoms are bonded to oxygen atoms, as in H₂SO₄ and H₃PO₄.
Weak acid: An acid that only partially dissociates into ions in aqueous solution, as H₂SO₃ does.
Amphoteric: Describes a substance that can react both as an acid and as a base.
Neutralisation: The reaction of an acid with a base to form a salt and water.
Electronegativity: The power of an atom to attract the pair of electrons in a covalent bond.
Hydrolysis: A reaction in which a bond in a compound is broken by reaction with water.