Ions & Ionic Bonds (Cambridge O Level Chemistry)

• 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

• 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