Dot-&-Cross Diagrams (Cambridge (CIE) AS Chemistry)

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 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 

Dot-and-cross diagrams of ionic compounds show how the atoms transfer their outer / valence electrons 

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

Dot-and-cross diagrams of covalent compounds show how atoms share their outer / valence electrons

Coordinate bonding

• Coordinate bonding or also called dative covalent bonding is formed when one atom provides both the electrons needed for a covalent bond

• In a displayed formula, the dative covalent bond is represented by an arrow

• The head of the arrow points away from the lone pair that forms the bond

Dot-and-cross diagrams of coordinate / dative covalent compounds

Dot-and-cross diagrams of coordinate / dative covalent compounds show how one of the atoms provides both the electrons in a coordinate / dative covalent bond

Incomplete & expanded octet rule

• Some species may contain more (expanded) or less (incomplete) than eight electrons in their outer shell

Dot-and-cross diagrams for the expanded octet rule

Dot-and-cross diagrams can show how atoms follow the expanded octet rule

Dot-and-cross diagrams for the incomplete octet rule

Dot-and-cross diagrams can show how the atoms in an electron deficient compound follow the incomplete octet rule

Odd number of electrons

• Some atoms in compounds may have an odd number of electrons in their valence shell

Dot-and-cross diagrams for compounds containing atoms with odd numbers of outer / valence electrons

Dot-and-cross diagrams can show how some compounds contain atoms with odd numbers of outer / valence electrons