OCR A-level Chemistry A Module 2 Definitions

-Atoms, ions and compounds -Amount of substance -Acids and Redox -Electron structure -Ionic bonding and structure -Covalent bonding -Shapes of molecules and ions -Electronegativity and polarity -Intermolecular forces -Hydrogen bonding

Isotope

An atom of the same element with the same number of protons and electrons but a different number of neutrons, so a different mass number

Atomic number

The number of protons in the nucleus

Mass number

The number of protons plus neutrons in the nucleus

Relative atomic mass

The weighted mean mass of an atom compared with 1/12 mass of carbon-12

Relative isotopic mass

The mass of an isotope compared with 1/12 the mass of carbon-12

Cation

A positively charged ion

Anion

A negatively charged ion

Mole

The amount of substance which contains 6.02×10²³ particles (the same number of atoms in exactly 12g of carbon-12)

Hydrated compound

A compound containing water molecules within it’s crystalline structure

Anhydrous compound

A compound not containing water molecules within it’s crystalline structure

Concentration

The amount (in mol) of a dissolved substance (per dm³)

Molar gas volume

One mole of a gas at room temperature occupies 24dm³

Atom economy

The percentage proportion of reactants that are converted into useful products

Percentage yield

The actual yield of a product as a percentage of the theoretical yield

Acid

A substance which releases H+ ions (proton donor)

Strong (acid)

Fully dissassociates when dissolved in water

Weak (acid)

Partially dissassociates when dissolved in water

Base

A substance which accepts H+ ions (proton acceptor)

Alkali

Bases that dissolve in water to release OH- ions

Standard solution

A solution that has a known concentration

Reduction

The gain of electrons

Oxidation

The loss of electrons

Redox reaction

A reaction involving reduction and oxidation

Empirical Formula

The simplest whole number ratio of atoms of each element present in a compound

Molecular Formula

The number and type of atoms of each element in a molecule

Orbital

A region of space around the nucleus that can hold up to two electrons, with opposite spins

Metallic bond

The attraction between a lattice of metal cations and delocalised outer shell electrons

Ionic bond

An electrostatic attraction between ions of opposite charge

Covalent bond

A shared pair of electrons between two nuclei

Molecule

A small unit of two or more atoms covalently bonded together

Double covalent bond

Two shared pairs of electrons between two nuclei

Triple covalent bond

Three shared pairs of electrons between two nuclei

Lone pair

A pair of electrons that is not involved with bonding

Dative covalent bond

A shared pair of electrons in which both bonded electrons are contributed by one of the atoms in the bond

Electronegativity

The ablility of an atom to attract the bonding pair of electrons in a covalent bond

Polar bond

A covalent bond between atoms with different electronegativities with positive and negative partial charges on the bonded atoms

Dipole

Positive and negative partial charges separated by a short distance in a molecule

Intermolecular forces

The weak attractive forces between molecules