Atoms consist of electrons surrounding a nucleus that contains protons and neutrons.
Protons and neutrons have a relative mass of 1 and electrons have a negligible mass. Neutrons are neutral, but protons and electrons are electrically charged. Protons have a relative charge of +1 and electrons have a relative charge of -1.
Although the word 'atom' comes from the Greek for indivisible, we now know that atoms are not the smallest particles of matter. Instead, they have a small central nucleus surrounded by even smaller particles called electrons.
The atoms of each element are represented by chemical symbols. These usually consist of one or two different letters, but sometimes three letters are used for newly-discovered elements. The first letter in a chemical symbol is always an UPPERCASE letter, and the other letters are always lowercase. So, the symbol for magnesium is Mg and…