Representing 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
Worked example
Draw a dot and cross diagram for lithium nitride
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 N3- ion
- Overall, three lithium atoms each donate an electron to one nitrogen atom, to form 3 x Li+ ions and 1 x N3-
- The overall ionic compound formed is Li3N