Ionic Bonding (Oxford AQA IGCSE Chemistry)

What is Ionic Bonding?

• 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, 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 a Cation

Formation of an Anion

• 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

• We can determine the charge an ion will have from the group the element is found in: 

  • Elements in Group 1 form ions with a 1+ charge

  • Elements in Group 2 form ions with a 2+ charge

  • Elements in Group 6 form ions with a 2- charge

  • Elements in Group 7 form ions with a 1- charge 

Group 1 & Group 7 Ions

• Sodium is a Group 1 metal so loses one outer electron to another atom to gain a full outer shell of electrons

  • A positive sodium ion with the charge 1+ is formed, Na⁺ 

• Chlorine is a Group 7 non-metal so gains one electron to have a full outer shell of electrons

  • A negative chloride ion with a charge of 1– is formed, Cl^–

• The ions are then attracted to one another and held together by electrostatic forces

• The formula of the ionic compound is thus NaCl

• Ionic bonds can be represented diagrammatically using dot-and-cross diagrams

  • The electrons from each atom should be represented by using solid dots and crosses

  • If there are more than two atoms, then hollow circles or other symbols / colours may be used to make it clear

  • The large square brackets should encompass each atom and the charge should be in superscript and on the right-hand side, outside the brackets

Diagram representing the formation of the ionic bond in sodium chloride