Chemistry Definitions

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Molecular ion
Two or more atoms covalently bonded with an overall charge
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Avogadro constant
Number of atoms in 12.000g of carbon-12.
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Mole
The amount of substance which contains the Avogadro constant of atoms, molecules or groups of ions.
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Molar mass
The mass of one mole of a substance
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Anhydrous (salt)
A salt which contains no water of crystallisation
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Hydrated
A salt which contains water of crystallisation
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Atomic number
The number of protons in (the nucleus of) an atom.
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Mass number
The total number of protons and neutrons in the nucleus of an atom
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Relative atomic mass (RAM)
The average (weighted mean) mass of an atom of an element relative to one-twelfth of the mass of an atom of carbon-12
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Relative isotopic mass (RIM)
The mass of an atom of an isotope of an element relative to one-twelfth of the mass of an atom of carbon-12.
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Isotopes
Atoms which have the same atomic number but a different mass number (contain the same number of protons but a different number of neutrons)
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Relative formula mass (RFM)
The average (weighted mean) mass of a formula unit relative to one-twelfth of the mass of an atom of carbon-12
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Relative molecular mass (RMM)
The average (weighted mean) mass of a molecule relative to one-twelfth of the mass of an atom of carbon-12.
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First ionisation energy
The energy required to convert one mole of gaseous atoms into gaseous ions with a single positive charge.
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Second ionisation energy
The energy required to convert one mole of gaseous ions with a single positive charge into gaseous ions with a double positive charge.
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Third ionisation energy
The energy required to convert one mole of gaseous ions with a double positive charge into gaseous ions with a triple positive charge.
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Covalent bond
The electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms.
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Co-ordinate (Dative) bond
A shared pair of electrons between two atoms. One atom provides both electrons.
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Octet rule
When reacting, an atom tends to gain, lose or share electrons to achieve eight in its outer shell.
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Electronegativity
The extent to which an atom attracts the bonding pairs of electrons in a covalent bond
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Polar bond
A covalent bond in which there is unequal sharing of the bonding electrons.
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Delocalised electrons
Outer electrons do not have fixed positions but move freely
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Intermolecular
Between neighbouring molecules
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van der Waals’ forces
The attraction between instantaneous and induced dipoles on neighbouring molecules.
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Permanent dipole-dipole attraction
Attraction between the positive end, δ+, of the permanent dipole on a molecule with the negative end, δ-, of the permanent dipole of a neighbouring molecule
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Hydrogen bond
The attraction between a lone pair of electrons on a very electronegative atom (i.e. N,O, F) in one molecule and a hydrogen atom in a neighbouring molecule, in which the hydrogen atom is covalently bonded to a very electronegative atom (N,O,F).
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Redox
Oxidation and reduction occur in the same reaction.
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Oxidation
Loss of electrons / Increase in oxidation state
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Reduction
Gain of electrons / Decrease in oxidation state
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Oxidising agent
Electron acceptor
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Reducing agent
Electron donor
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Disproportionation
Oxidation and reduction of the same element in the same reaction.
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Strong acid/base
Fully dissociates in solution.
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Weak acid/ base
Partially dissociates in solution.
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Molarity
Concentration in mol dm-3 expressed using M.
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Concentration
Number of moles or mass present in a stated volume
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Standard solution
A solution for which the concentration is known.
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Other cards in this set

Card 2

Front

Number of atoms in 12.000g of carbon-12.

Back

Avogadro constant

Card 3

Front

The amount of substance which contains the Avogadro constant of atoms, molecules or groups of ions.

Back

Preview of the back of card 3

Card 4

Front

The mass of one mole of a substance

Back

Preview of the back of card 4

Card 5

Front

A salt which contains no water of crystallisation

Back

Preview of the back of card 5
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