Ionic Bonding (WJEC GCSE Chemistry)

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

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

Diagram to show the formation of a chloride ion

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

Sodium transfers its outer electron to chlorine