Glossary
The terms of this app, from A to Z, each with the page that explains it.
- Atomic number
The atomic number tells how many protons an atom has. Every element has its own atomic number.
- Boiling point
The temperature at which a liquid becomes gaseous. For a pure substance it is always the same.
- Change of state
In a change of state such as melting or evaporating the substance stays the same. Only the state of matter changes.
- Chemical reaction
In a chemical reaction substances turn into other substances. The new substances have different properties from the old ones.
- Coefficient
A coefficient is the big number in front of a formula. It tells how often the formula occurs.
- Compound
A compound consists of atoms of different elements joined in a fixed ratio, for example water or carbon dioxide.
- Electron
An electron is a particle in the electron shell with a negative charge.
- Element symbol
The element symbol is the abbreviation of an element with one or two letters, for example C for carbon.
- Formula
A formula uses element symbols to show which atoms a substance is made of. A small subscript number, the index, tells how many atoms there are.
- Group
A group is a column in the periodic table. Elements in one group have similar properties.
- Main group
The eight main groups are groups 1, 2 and 13 to 18 of the periodic table. They are numbered I to VIII.
- Mass number
The mass number is the number of protons and neutrons together.
- Melting point
The temperature at which a solid becomes liquid. For a pure substance it is always the same.
- Metal
Metals conduct electricity and heat well, can be formed into sheets and wires and have a metallic lustre.
- Metalloid
Metalloids stand in the periodic table between metals and non-metals and cannot clearly be put into either group. Examples are boron and silicon.
- Mixture
A mixture consists of several substances, for example air, milk or granite.
- Molecule
A molecule is a small particle made of several joined atoms, for example a water molecule.
- Neutron
A neutron is a particle in the nucleus with no charge.
- Non-metal
Non-metals do not have these metal properties. Examples are hydrogen, carbon, nitrogen, oxygen and sulfur.
- Nucleus
The nucleus is in the centre of the atom. It consists of protons and neutrons.
- Particle model
In the particle model every substance consists of very small particles, which you imagine as balls.
- Period
A period is a row in the periodic table. The number of the period tells how many shells an atom has.
- Proton
A proton is a particle in the nucleus with a positive charge.
- Pure substance
A pure substance consists of only one kind of substance, for example pure water or pure oxygen.
- Reaction equation
A reaction equation describes a reaction with formulas. The starting substances are on the left of the arrow, the products on the right.