CIE A Level Chemistry复习笔记1.3.16 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 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

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 dative covalent compounds in which one of the atoms provides both the electrons in a covalent bond

Incomplete & expanded octet rule

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

Expanded octet rule

Incomplete octet rule

Odd number of electrons

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

Incomplete octet rule