Unit 1-Glossary

An aqueous solution of a substance which has a pH less than 7. There is an excess of hydrogen ions, H+ in the solution.

An aqueous solution of a substance with a pH greater than 7 . There is an excess of hydroxide ions, OH- , in the solution.

Indicates that the substance has been dissolved in water.

The smallest particle that can be obtained by chemical means. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons

The number of protons in the nucleus of the atom.

A compound which neutralises an acid to form a salt and water. Bases can be soluble or insoluble. Metal oxides and metal hydroxides are bases. Soluble bases form alkaline solutions

Formed when non-metal atoms join together by sharing electrons to achieve a full outer shell of electrons (electron arrangement the same as the nearest noble gas, group 0).

A compound of non-metal atoms held together by covalent bonds.

A large structure of covalently bonded atoms.

Contain two atoms. They can be elements e.g. Hydrogen, Oxygen, Nitrogen, Fluorine, Chlorine, Bromine and Iodine (H2,O2,N2,F2,Cl2,Br2,I2) or compounds e.g. hydrogen chloride, HCl

The process of breaking down of an ionic compound into its elements by the use of an electric current.

A very small negatively-charged particle found in the space surrounding the nucleus of an atom.

The arrangement of electrons in shells (or energy levels) around the nucleus of an atom.

A substance containing only one kind of atom. It cannot be broken down further by chemical means.

In an endothermic reaction, energy is taken in from the surroundings. There is a decrease in temperature.

A reaction in which heat energy is released. There is a rise in temperature.

A vertical column in the periodic table

A group of very reactive non-metal elements in Group 7 of the periodic table.

A substance which changes colour at a particular pH.

A charged particle formed by loss or gain of electrons. When atoms lose an electron they become a positive ion (usually metals). When they gain an electron they become a negative ion (usually a non-metal).

An ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron). This is usually a metal/non-metal compound.

Compounds with the same molecular formula but with a different structural formula.

Atoms of the same element that have different numbers of neutrons (different mass number).