Chemistry vocabulary: 18 terms with definitions

The smallest unit of an element that still has its properties.

A pure substance made of only one kind of atom, such as oxygen or gold.

A substance made of two or more elements chemically joined, such as water, H₂O.

Two or more atoms bonded together, such as a molecule of oxygen gas, O₂.

A particle with a positive charge in the nucleus of an atom; the number of protons decides which element it is.

A particle with no charge in the nucleus of an atom.

A tiny particle with a negative charge that moves around the nucleus of an atom.

A form of an element with a different number of neutrons, such as carbon-14.

The chart of the elements in order of atomic number, with elements of similar properties in the same column.

The electrons in an atom's outer shell, which take part in chemical bonds.

A change in which substances turn into new substances, such as iron rusting.

A substance that speeds up a chemical reaction without being used up.

A reaction in which a substance loses electrons, often by combining with oxygen, as when iron rusts.

A substance with a pH below 7, such as lemon juice or vinegar.

A substance with a pH above 7, such as baking soda or soap.

A mixture in which one substance dissolves evenly in another, such as salt water.

Two or more substances mixed but not chemically joined, which can be separated again, such as sand and iron filings.

A very large molecule made of many small repeating units, such as plastic, rubber or DNA.