Ion: GCSE Chemistry Definition

What is an ion?

In GCSE chemistry, an ion is an electrically charged atom which is formed by the loss or gain of electrons. Atoms lose or gain electrons to obtain full outer shells of electrons. If an atom loses electrons, it will form positively charged ions (cations), and if it gains electrons it will form negatively charged ions (anions). 

For example, a sodium atom has 1 electron in its outer shell. It loses this electron to another atom. The sodium ion formed has 11 positively charged protons but only 10 negatively charged electrons, so will have a 1+ charge overall. Chlorine has 7 electrons in its outer shell, so it gains one electron from sodium to complete it. The ion formed has 17 protons but 18 electrons so has a 1- charge overall. The charge of an ion is determined by the number of electrons lost or gained. There are strong electrostatic forces of attraction between the oppositely charged ions.

Ion Revision Resources to Ace Your Exams

You can boost your GCSE chemistry grade by using our ion resources to strengthen your understanding on ion formation. Use our topic questions to practice drawing dot and cross diagrams for a range of ionic compound and consolidate using flashcards. 

Explore Our GCSE Chemistry Revision Resources