CIE AS Chemistry (9701) exams from 2022

Revision Notes

1.3.16 Dot-&-Cross Diagrams

Dot & Cross Diagrams

  • Dot & 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

 

Chemical Bonding Ionic Dot & Cross, downloadable AS & A Level Chemistry revision notes

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

 

Chemical Bonding Covalent Dot & Cross 1, downloadable AS & A Level Chemistry revision notes

Chemical Bonding Covalent Dot & Cross 2 (1), downloadable AS & A Level Chemistry revision notes

Chemical Bonding Covalent Dot & Cross 2 (2), downloadable AS & A Level Chemistry revision notes

Chemical Bonding Covalent Dot & Cross 3 (1), downloadable AS & A Level Chemistry revision notes

Chemical Bonding Covalent Dot & Cross 3 (2), downloadable AS & A Level Chemistry revision notes

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

 

Chemical Bonding Dative Covalent Dot & Cross, downloadable AS & A Level Chemistry revision notes

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

Chemical Bonding Expanded Covalent Dot & Cross (1), downloadable AS & A Level Chemistry revision notes Chemical Bonding Expanded Covalent Dot & Cross (2), downloadable AS & A Level Chemistry revision notes

Expanded octet rule

 

Chemical Bonding Incomplete Covalent Dot & Cross, downloadable AS & A Level Chemistry revision notes

Incomplete octet rule

Odd number of electrons

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

 

Chemical Bonding Odd Number of Electrons Dot & Cross, downloadable AS & A Level Chemistry revision notes

Incomplete octet rule

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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