1.4.5 Dot & 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

Ionic compounds

• Ionic bonds are formed when metal atoms transfer electrons to a non-metal to form a positively charged and negatively charged ion
• The atoms achieve a noble gas configuration

Dot-and-cross diagrams of ionic compounds in which one of the atoms transfers their valence electrons to the other

Covalent compounds

• The atoms in covalent compounds will share their outer valence electrons to achieve a noble gas configuration

Dot-and-cross diagrams of covalent compounds in which the atoms share their valence electrons

Answer

• • Lithium is a Group 1 metal, so it loses its 1 electron from its outer shell
  • This forms a Li⁺ ion
  • Nitrogen is a Group 5 non-metal, so it needs to gain 3 electrons to complete its outer shell
  • This forms an N^3- ion
  • Overall, three lithium atoms each donate an electron to one nitrogen atom, to form 3 x Li⁺ ions and 1 x N^3-
  • The overall ionic compound formed is Li₃N