# Key definitions - Chemistry 1.1

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Isotopes
are atoms of the same element with different numbers of neutrons.
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Atomic (Proton) Number
is the number of protons in the nucleus of an atom.
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Mass (Nucleon) Number
is the number of particles (protons and neutrons) in the nucleus.
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An ion
is a positively or negatively charged atom or (covalently bonded) group of atoms (a molecular ion).
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Relative isotopic mass
is the mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12.
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Relative atomic mass, Ar
is the weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12.
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Relative molecular mass, Mr
is the weighted mean mass of a molecule compared with one-twelfth of the mass of an atom of carbon-12.
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Relative formula mass
is the weighted mean mass of a formula unit compared with one-twelfth of the mass of an atom of carbon-12.
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Amount of substance
is the quantity whose unit is the mole. Chemists use 'amount of substance' as a means of counting atoms
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is the number of atoms per mole of the carbon-12 isotope.
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A mole
is the amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope.
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Molar mass, M
Is the mass per mole of a substance.
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The empirical formula
is the simplest whole-number ratio of atoms of each element present in a compound.
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A molecule
is a small group of atoms held together by covalent bonds.
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The molecular formula
is the actual number of atoms of each element in a molecule.
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Molar volume
is the volume of a gas. At room temperature and pressure, the molar volume is approx. 24.0 dm ^3 mol-1.
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The concentration of a solution
is the amount of solute in mol, dissolved per 1dm^3(1000cm^3) of solution.
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A standard solution
is a solution of known concentration. Standard solutions are normally used in titrations to determine unknown information about another substance.
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A species
is any type of particle that takes place in a chemical reaction.
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Stoichiometry
is the molar relationship between the relative quantities of substances taking part in a reaction.
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An acid
is a species that is a proton donor.
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A base
is a species that is a proton acceptor.
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An alkali
is a type of base that dissolves in water, forming hydroxide ions OH-(aq) ions.
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A salt
is any chemical compound formed from an acid when a H+ ion from the acid has been replaced by a metal ion or another positive ion, such as the ammonium ion, NH4+
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A cation
is a positively charged ion.
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An anion
is a negatively charged ion.
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Hydrated
refers to a crystalline compound containing water molecules.
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Anhydrous
refers to a substance that contains no water molecules.
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Water of crystallisation
refers to water molecules that form an essential part of the crystalline structure of a compound.
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An oxidation number
is a measure of the number of electrons that an atom uses to bond with atoms of another element. Oxidation numbers are derived from a set of rules.
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Oxidation
is loss of electrons or an increase in oxidation number.
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Reduction
is gain of electrons or a decrease in oxidation number.
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A redox reaction
is a reaction in which both oxidation and reduction both take place.
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A reducing agent
is a reagent that reduces (adds electrons to) another species.
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An oxidising agent
is a reagent that oxidises (takes electrons away from) another species.
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## Other cards in this set

### Card 2

#### Front

is the number of protons in the nucleus of an atom.

#### Back

Atomic (Proton) Number

### Card 3

#### Front

is the number of particles (protons and neutrons) in the nucleus.

### Card 4

#### Front

is a positively or negatively charged atom or (covalently bonded) group of atoms (a molecular ion).

### Card 5

#### Front

is the mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12.

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