Chemical Symbols and Chemical Formulae

Every element has a chemical symbol which can be used to represent it. An element's chemical symbol is always either a single capital letter or a capital letter followed by a lowercase letter.

For example, carbon's chemical symbol is C and helium's chemical symbol is He.

An element's chemical symbol is not always a shortened version of its name. For example, potassium's chemical symbol is K and sodium's chemical symbol is Na.

Particles can be represented by chemical formulae

Every atom and ion can be represented by a chemical formula.

The chemical formula for an atom is simply its element's chemical symbol.

For example, to represent a carbon atom we would simply write:

C

and to represent a sodium atom we would simply write:

Na

The chemical formula of an ion is its element's chemical symbol followed by the ion's relative charge.

For example, the chemical formula for an aluminium ion with a relative charge of +3 is:

Al³⁺

Notice that the relative charge is raised up above the line that the chemical formula is written on (this is called superscript).

Also, notice that the number (3) is written before the sign (+). Usually, if we were describing the relative charge of the ion, we would write +3, but when we are writing the ion's chemical formula we swap the order and write 3+.

So, for example, the chemical formula for an oxide ion with a relative charge of -2 is:

O^2-

If the charge of an ion is +1 or -1, then we don't write the 1, we simply write + or -.

For example, the chemical formula for a sodium ion with a relative charge of +1 is:

Na⁺

and the chemical formula for a fluoride ion with a relative charge of -1 is:

F^-

The rules for writing the chemical formulae of atoms and ions are summarised below:

• An atom's chemical formula is simply the chemical symbol of its element.
• An ion's chemical formula is the chemical symbol of its element, followed by its relative charge, written in superscript.
• The number part of the relative charge is written before the sign (+ or -).
• If the relative charge is +1 or -1 then it is simply written as + or -.

We can represent multiple atoms or ions using numbers

Sometimes, we want to refer to a certain number of atoms or ions. For example, we might want to refer to six helium atoms. We can do this by placing a number before the chemical formula. So, six helium atoms would be represented by the following:

6He

If we wanted to represent 7 aluminium ions, each with a relative charge of +3, we would write the following:

7Al³⁺

Subatomic particles also have symbols

We can also use symbols to represent protons, neutrons and electrons.

The symbol for a proton is:

p⁺

The symbol for a neutron is:

n⁰

The symbol for an electron is:

e^-

Notice that the part in superscript in each symbol tells you about the particle's relative charge (+1 for a proton, 0 for a neutron, -1 for an electron).

Flashcards

Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.