You have learned about the following concepts in this course:
Each type of atom contains a characteristic number of protons in a central nucleus and an equal number of electrons in layers surrounding the nucleus.
Elements are substances that consist of only one type of atom. Compounds contain two or more elements combined together. There are two kinds of bond between atoms: covalent and ionic.
Molecules are the smallest units in which elements and/or compounds can exist covalently bonded together.
Ions are formed by atoms or groups of atoms gaining or losing electrons.
Chemical formulas describe the number of atoms present in elements, ions and compounds.
Balanced chemical equations describe, using chemical formulas, the reactants and products in a chemical reaction.
Concentration is the mass of a substance dissolved in a given volume (usually 1 litre) of a liquid.