Definitions - Atoms, Bonds & Groups Flashcards
Acid
A species that is a proton (H+) donor.
Alkali
A type of base that dissolves in water, forming hydroxide ions (OH-).
Amount of substance
The quantity whose unit is the mole. Chemists use “amount of substance” as a means of counting atoms.
Anhydrous
A substance which contains no water molecules.
Anion
A negatively charged ion.
Atomic orbital
Region within an atom which can hold up to two electrons, opposite spin.
Atomic number
The number of protons in the nucleus of an atom.
Avogadro Number (N_A)
The number of atoms per mole of the carbon-12 isotope (6.02 x 10^23 mol^-1)
Base
A species that is a proton (H+) acceptor.
Cation
A positively charged ion.
Compound
A substance formed from two or more chemically bonded elements in a fixed ratio; usually shown by a chemical formula.
Concentration
The amount of solute, in moles, per cubic decimeter of solution.
Coordinate Bond (= Dative Bond)
A shared pair of electrons which has been provided by one of the bonding atoms only (also called a Dative bond).
Dehydration
An elimination reaction in which water is removed from a saturated molecule to make it unsaturated.
Delocalised electrons
Electrons which are shared between more than two atoms.
Displacement reaction
A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of the latter’s ions.
Disproportionation
The oxidation and reduction of the same element in a redox reaction.
Electron configuration
The arrangement of electrons in an atom.
Electronegativity
A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.
Electron Shielding
The repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the positive nucleus on the outer-shell electrons.
Empirical formula
The simplest whole number ratio of atoms of each element present in a compound.
Giant covalent lattice
A three-dimensional structure of atoms, bonded by strong covalent bonds.
Giant ionic lattice
A three-dimensional structure of oppositely charged ions, bonded together by strong ionic bonds.
Giant metallic lattice
A three-dimensional structure of positive metal ions and delocalised electrons, bonded together by strong metallic bonds.
Group
A vertical column in the periodic table. Elements in the same group have similar chemical properties and have the same number of outer shell electrons.
Hydrogen bond
A strong dipole-dipole attraction between an electron deficient hydrogen atom on one molecule and a lone pair of electrons on a highly electronegative atom on a different molecule.
Intermolecular force
An attractive force between neighbouring molecules. Intermolecular forces can be van der Waals’ forces (induced dipole-dipole forces), permanent dipole-dipole forces or hydrogen bonds.
Ion
A positively or negatively charged atom or (covalently bonded) group of atoms (a molecular ion).
Ionic Bonding
The electrostatic attraction between oppositely charged ions.
First Ionisation Energy
The energy required to remove 1 electron from each atom in 1 mol of gaseous atoms to form 1 mol of gaseous 1+ ions.
Second Ionisation Energy
The energy required to remove 1 electron from each ion in 1 mol of gaseous 1+ ions to form 1 mol of gaseous 2+ ions.
Successive Ionisation Energy
A measure of the energy required to remove 1 electron in turn; e.g. the second ionisation energy is the energy required to remove 1 electron from each ion in 1 mol of gaseous 1+ ions to form 1 mol of gaseous 2+ ions.
Isotopes
Atoms of the same element with a different number of neutrons.
Lone pair
An outer-shell pair of electrons not involved in chemical bonding.
Mass (nucleon number)
The number of particles (protons and neutrons) in the nucleus.
Metallic bonding
The electrostatic attraction between the positive metal ions and delocalised electrons.
Molar mass (M_R)
The mass per mole of substance. The units of molar mass are g/mol.
Molar volume
The volume per mole of gas. The units of molar volume are cubic decimeter per mole (dm^3/mol). At room temperature and pressure the molar volume is approximately 24.0 dm^3/mol.
Mole
The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope.
Oxidation
Loss of electrons or an increase in oxidation number.
Oxidation number
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.
Oxidising agent
A reagent that oxidises (takes electrons from) another species.
Period
A horizontal row of elements in the Periodic Table. Elements show trends in properties across a period.
Periodicity
A regular periodic variation of properties of elements with atomic number and position in the Periodic Table.
Permanent dipole
A small charge difference across a bond resulting from a difference in electronegativities of the bonded atoms.
Permanent dipole-dipole force
An attractive force between permanent dipoles in neighbouring polar regions.
Polar covalent bond
A bond with a permanent dipole.
Polar molecule
A molecule with an overall dipole, taking into account any dipoles across bonds.
Precipitation reaction
The formation of a solid from a solution during a chemical reaction. Precipitates are often formed when two aqueous solutions are mixed together.
Principal quantum number, n
A number representing the relative overall energy of each orbital, which increases with distance from the nucleus. The sets of orbitals with the same n value are referred to as electrons shells or energy levels.
Redox reaction
A reaction in which both reduction and oxidation take place.
Reducing agent
A reagent that reduces (adds electrons to) another species.
Relative atomic mass
The weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12.
Relative formula mass
The weighted mean mass of a formula unit compared with 1/12 of the mass of an atom of carbon-12.
Relative isotopic mass
The mass of an isotope compared with 1/12 of the mass of an atom of carbon-12.
Relative molecular mass
The weighted mean mass of a molecule compared with 1/12 of the mass of an atom of carbon-12.
Salt
A 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+)
Shell
A group of atomic orbitals with the same principal quantum number, n. Also known as a main energy level.
Simple molecular lattice
A three-dimensional lattice of molecules, bonded together by weak intermolecular forces.
Species
Any type of particle that takes part in a chemical reaction.
Spectator ions
Ions that are present but take no part in a chemical reaction.
Standard solution
A solution of known concentration. Standard solutions are normally used in titrations to determine unknown information about another substance.
Sub-shell
A group of the same type of atomic orbitals (s, p, d or f) within a shell.
Substitution reaction
A reaction in which an atom or group of atoms is replaced with a different atom or group of atoms/
Thermal decomposition
The breaking up of a chemical substance with heat into at least two chemical substances.
van der Waals’ force
Very weak attractive forces between induced dipoles in neighbouring molecules.
Water of crystallisation
Water molecules that form an essential part of the crystalline structure of a compound.
