Learn: Formulae of elements, compounds and ions

Welcome!Today we'll learn about the formulae of elements, compounds, and ions. Understanding how to write and interpret chemical formulae is essential for GCSE Chemistry. Let's take it step by step!

What are chemical formulae?A chemical formula shows the types and numbers of atoms in a substance. It is used to represent elements, compounds, and ions. This helps us understand how substances are made and how they react.

Formulae of elementsElements are substances made of only one type of atom. Some elements exist as single atoms, like helium (He), while others exist as molecules, like oxygen (O2). A molecule is two or more atoms bonded together.

Formulae of compoundsA compound is a substance made of two or more different types of atoms that are chemically bonded. For example, water has the formula H2O, meaning each molecule contains two hydrogen atoms and one oxygen atom.

Formulae of ionsAn ion is an atom or group of atoms with a charge due to the loss or gain of electrons. For example, sodium loses one electron to form Na+, while chlorine gains one electron to form Cl-.

Combining ions to form compoundsTo form a compound, positive and negative ions combine to create a neutral substance. For example, NaCl is made of one sodium ion (Na+) and one chloride ion (Cl-), balancing the charges.

Balancing chargesWhen writing the formula for a compound, the total positive and negative charges must balance to zero. For example, in aluminium oxide, Al2O3, two Al3+ ions balance three O2- ions.

Review Time!Great work! You've learned about the formulae of elements, compounds, and ions. Now let's test your understanding with a few questions.