How are Ions Formed? (Edexcel IGCSE Chemistry (Modular))

Revision Note

Test yourself

Formation of ions

  • An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons

  • This loss or gain of electrons takes place to obtain a full outer shell of electrons

  • The electronic structure of ions of elements in groups 1, 2, 3, 5, 6 and 7 will be the same as that of a noble gas - such as helium, neon, and argon

  • Negative ions are called anions and form when atoms gain electrons, meaning they have more electrons than protons

  • Positive ions are called cations and form when atoms lose electrons, meaning they have more protons than electrons

  • All metals lose electrons to other atoms to become positively charged ions

  • All non-metals gain electrons from other atoms to become negatively charged ions

Formation of cations

1-6-1-formation-of-ions-1

Diagram showing the formation of the sodium ion

Formation of anions

1-6-1-formation-of-ions-2

Diagram showing the formation of the chloride ion

Examiner Tip

The number of electrons that an atom gains or loses is the same as the charge.

For example, if a magnesium atom loses 2 electrons, then the charge will be 2+, if a bromine atom gains 1 electron then the charge will be 1-.

Last updated:

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Alexandra Brennan

Author: Alexandra Brennan

Expertise: Chemistry

Alex studied Biochemistry at Newcastle University before embarking upon a career in teaching. With nearly 10 years of teaching experience, Alex has had several roles including Chemistry/Science Teacher, Head of Science and Examiner for AQA and Edexcel. Alex’s passion for creating engaging content that enables students to succeed in exams drove her to pursue a career outside of the classroom at SME.

Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.