All Chemistry Definitions Grade 11

RBHS

Molar Mass (M)

Molar mass (symbol M) is the mass of one mole of any substance, expressed in grams per mole (g.mol-1).

One mole

It is the amount of substance having the same number of particles as there are atoms in 12 g carbon-12.

Molar mass

The mass of one mole of a substance measured in g-mol-1

Avogadro's Law

One mole of any gas occupies the same volume at the same temperature and pressure.

Concentration

It is the number of moles of solute per cubic decimetre of solution.

Empirical formula

It is the simplest whole-number ratio of atoms in a compound.

Molecular formula

It is the formula that shows all the atoms in a compound.

Element

An element is a collection of atoms all with the same atomic number.

Atomic number

The atomic number, Z, of an element is the number of protons in each atom of the element. It is unique to each element.

Mass number

The mass number, A, of an isotope is the number of protons and neutrons in the nucleus of each atom of an isotope. Also known as the number of nucleons.

Isotopes

Different atoms of the same element, having the same atomic number but different mass numbers. This is so because the number of neutrons

Intermolecular forces

are the forces of attraction or repulsion between molecules.

Intramolecular forces or interatomic forces:

are the forces between atoms or 'inside' molecules which keep atoms together.

Dipole-dipole forces

are the forces between polar molecules.

Induced dipole forces or London forces:

are the forces between non-polar molecules.

Hydrogen bonds

are the forces between molecules in which a hydrogen atom that is covalently bonded to a small, highly electronegative atom is attracted to a lone pair of electrons on an atom in a neighbouring molecule.

Boiling point

is the temperature at which the vapour pressure of a substance equals atmospheric pressure.

Melting point

is the temperature at which the solid and liquid phases of a substance are at equilibrium.

Vapour pressure

is the pressure exerted by a vapour at equilibrium with its liquid in a closed system.

Heat of reaction (AH)

is the energy absorbed or released in a chemical reaction.

Exothermic reactions

are reactions that release energy.

Endothermic reactions

are reactions that absorb energy.

A reversible reaction

is a reaction where products can be converted back into reactants.

Activation energy

is the minimum energy needed for a reaction to take place.

Activated complex

is the unstable transition state from reactants to products in a chemical reaction.

A positive catalyst

is a substance that increases the rate of a chemical reaction without itself undergoing a permanent change.

Chemical bonding

The mutual interaction between atoms resulting from the attraction and repulsion between their nuclei and valence electrons.

Bond energy

The energy needed to break chemical bonds to form neutral atoms.

Bond length

The average distance between the nuclei of two bonded atoms.

lonic bonding

The electrostatic interaction between cations and anions that involves the transfer of electrons and forms a three-dimensional lattice structure.

Covalent bonding

The electrostatic interaction that involves the sharing of electrons between atoms to form molecules.

Dative covalent bonding

A bond that involves the sharing of an electron pair between atoms where both electrons are donated by one of the two atoms.

Molecule

It is a neutral group of two or more atoms which are bonded together sufficiently strongly to act as a unit in chemical reactions.

Bonding (shared) pair

It is the pair of electrons that is shared between two atoms in a covalent bond.

Lone pair

It is a pair of electrons in the valence shell of an atom that is not shared with another atom.

Electronegativity

It is a measure of the tendency of an atom to attract a shared pair of electrons towards itself.

Polar covalent bond

A bond that is formed as a result of the unequal sharing of electrons between two atoms.

Non-polar (pure) covalent bond

The bond that is formed as a result of an equal sharing of electrons between two atoms.