Ions & Ionic Bonds (Cambridge (CIE) O Level Chemistry): Revision Note

The Formation of Ions

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

• An atom will lose or gain electrons to become more stable

• The loss or gain of electrons takes place to gain a full outer shell of electrons which is a more stable arrangement of electrons

• The electronic configuration of an ion will be the same as that of a noble gas – such as helium, neon and argon

Formation of positively charged sodium ion

Formation of negatively charged chloride ion

 Ionisation of metals and non-metals

• Metals: all metals can lose electrons to other atoms to become positively charged ions, known as cations

• Non-metals: all non-metals can gain electrons from other atoms to become negatively charged ions, known as anions

The Formation of Ionic Bonds

• Ionic compounds are formed when metal atoms react with non-metal atoms

• Metal atoms lose their outer electrons which the non-metal atoms gain to form positive and negative ions

• The positive and negative ions are held together by strong electrostatic forces of attraction between opposite charges

• This force of attraction is known as an ionic bond and they hold ionic compounds together

Dot-and-cross diagrams

• Dot and cross diagrams are diagrams that show the arrangement of the outer-shell electrons in an ionic or covalent compound or element

  • The electrons are shown as dots and crosses

• In a dot and cross diagram:

  • Only the outer electrons are shown

  • 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

Electrostatic forces between the positive Na ion and negative Cl ion