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Year 10
Edexcel
Foundation

Forming covalent bonds

I can use dot and cross diagrams to explain how electrons are shared to form a covalent bond.

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Year 10
Edexcel
Foundation

Forming covalent bonds

I can use dot and cross diagrams to explain how electrons are shared to form a covalent bond.

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Lesson details

Key learning points

  1. In a covalent bond, two non-metal atoms share a pair of electrons (from their outer shells).
  2. For every one electron needed to complete the outer shell of an atom, one covalent bond will form.
  3. Atoms can share multiple pairs of electrons.
  4. Displayed formulae of covalent substances are a model, showing lines to represent shared pairs of electrons.

Keywords

  • Molecule - A particle consisting of a fixed number of (two or more) non-metal atoms covalently bonded together.

  • Covalent bond - The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

  • Dot and cross diagram - Is used to show how chemical bonds are formed between atoms. The electrons from one atom are shown as dots and the electrons from the other atom are shown as crosses.

  • Empirical formula - Shows the simplest whole number ratio of atoms of each element in a compound.

  • Displayed formula - A 2D model of a covalent substance, showing all its atoms and bonds. Lines are used to represent shared pairs of electrons.

Common misconception

The covalent bond is the shared pair of electrons; both electrons must come from different atoms. The central atom is responsible for the formation of covalent bonds as they want a full outer shell.

All chemical bonds are an electrostatic force of attraction between positive and negative charges. The sharing of electrons is the process by which covalent bonds are formed. Avoid using anthropomorphic analogies to explain how covalent bonds form.

Use molecular modelling kits to demonstrate the number of covalent bonds each atom can from and to point out which atom is sharing its outer shell electron. Encourage students to think about the chemical elements as chemicals and build on previous learning about why chemical reactions occur.
Teacher tip

Equipment

molecular modelling kits

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
Why do atoms form chemical bonds?
To increase their mass.
Correct answer: To achieve a full outer electron shell.
To lose all their electrons.
To become larger in size.
Q2.
Which type of bond forms between atoms that have transferred electrons from one atom to another?
Covalent bond
Correct answer: Ionic bond
Metallic bond
Q3.
What type of elements typically form ionic bonds?
Two non-metals.
Two metals.
Correct answer: A metal and a non-metal.
Q4.
How many outer-shell electrons does an oxygen atom have?
2
4
Correct answer: 6
8
16
Q5.
A is a particle consisting of two or more non-metal atoms bonded together. It can be made up of the same or different elements.
Correct Answer: molecule
Q6.
Arrange the following molecules by the number of covalent bonds each has, from least to most:
1 - H₂
2 - O₂
3 - N₂

Exit quiz

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6 Questions

Q1.
What is a covalent bond?
A bond between two metal atoms.
A bond between a metal and a non-metal atom.
Correct answer: A bond where two non-metal atoms share a pair of electrons.
A bond formed of ions, where atoms have transferred electrons.
Q2.
How many covalent bonds will an atom form if it needs three electrons to complete its outer shell?
1
2
Correct answer: 3
4
Not enough information is known
Q3.
What does a displayed formula of a covalent substance show?
Correct answer: All of the atoms present in the substance.
Correct answer: All of the bonds between atoms.
A shorthand version of the structure, showing only some of the atoms.
A shorthand version of the structure, showing only some of the bonds.
Correct answer: Each line drawn represents a shared pair of electrons.
Q4.
What is the purpose of a dot and cross diagram?
To show the physical state of a substance.
Correct answer: To show how chemical bonds are formed between atoms.
To represent the empirical formula of a compound.
To show the arrangement of metal ions.
Q5.
A is a particle consisting of a fixed number of non-metal atoms covalently bonded together.
Correct Answer: molecule
Q6.
Atoms can share multiple pairs of electrons to achieve full outer shells, leading to double or covalent bonds.
Correct Answer: triple