Ionic Bonding (WJEC GCSE Chemistry)

Revision Note

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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 Group 1, 2, 6 and 7 ions will be the same as 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

Diagram to show the formation of a sodium ion

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A sodium atom loses its outer shell electron to form a positive ion

Diagram to show the formation of a chloride ion

nacl-ionic-bonding

A chlorine atom gains an electron to form a chloride ion

  • The positive and negative charges are held together by the strong electrostatic forces of attraction between oppositely charged ions
    • This is what holds ionic compounds together

Dot & Cross Diagrams

  • These show the arrangement of the electrons in an ionic compound
  • The electrons are shown as dots and crosses
  • The charge of the ion is spread evenly which is shown by using brackets
  • The charge on each ion is written at the top right-hand corner

Dot and cross diagram of sodium chloride

oppositely-charged-ions-attraction-due-to-electrostatic-attraction-igcse-and-gcse-chemistry-revision-notes

Sodium transfers its outer electron to chlorine

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-.

When drawing dot and cross diagrams, make sure you use the dot and cross notation so that it is clear which electrons have been transferred. 

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Alexandra

Author: Alexandra

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.