AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The electron transfer during the formation of an ionic compound can be…
Full specification wording
Ionic bonding: The electron transfer during the formation of an ionic compound can be represented by a dot and cross diagram, eg for sodium chloride
A dot and cross diagram shows the electron transfer that forms an ionic compound.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 2 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A dot and cross diagram shows the electron transfer that forms an ionic compound. For sodium chloride, draw the sodium atom with its outer-shell electron as a dot and the chlorine atom with its outer-shell electrons as crosses. Show the transfer of the sodium outer-shell electron to the chlorine atom. After transfer, draw the sodium ion with no outer-shell electron and a 1⁺ charge, and the chloride ion with eight outer-shell electrons (the original seven crosses plus the transferred dot) and a 1⁻ charge. Use square brackets around each ion and include the charge outside the bracket. The diagram represents the electron transfer and the resulting ions, not the sharing of electrons.
What earns the marks
- Draw the outer-shell electrons of each atom using dots for one atom and crosses for the other.
- Show the transfer of one electron from the sodium atom to the chlorine atom.
- Draw the sodium ion with no outer-shell electrons and a 1⁺ charge.
- Draw the chloride ion with eight outer-shell electrons and a 1⁻ charge.
- Use square brackets around each ion and place the charge outside the bracket.
- Ensure the diagram represents electron transfer, not electron sharing.
Common mistakes and how to put them right
Drawing the ions without square brackets or charges.
Put it right by enclosing each ion in square brackets and writing the charge outside, such as [Na]⁺ and [Cl]⁻.
Showing the transferred electron as a shared pair between the atoms.
Put it right by showing the electron fully transferred to the non-metal atom.
Giving the chloride ion seven outer-shell electrons instead of eight.
Put it right by adding the transferred electron to the seven original outer-shell electrons.
Exam tips
- Use dots for one atom and crosses for the other so the transferred electron is easy to track.
- Check that the total number of outer-shell electrons shown after transfer equals eight for the negative ion and zero for the positive ion.
- Include the charge on each ion outside the square brackets to show the ionic compound formed.
Try the lesson
The start of the Ionic bonding: The electron transfer during the formation of an ionic compound can be represented by a dot and cross diagram, eg for sodium chloride lesson, made from checked teaching notes for this specification point.
Have a go first
In a dot and cross diagram for sodium chloride, the single electron in the outer shell of a sodium atom is shown transferred to a chlorine atom. What charge does the sodium ion formed in this transfer carry?
Listen
A dot and cross diagram shows the electron transfer that forms an ionic compound. For sodium chloride, draw the sodium atom with its outer-shell electron as a dot and the chlorine atom with its outer-shell electrons as crosses. Show the transfer of the sodium outer-shell electron to the chlorine atom. After transfer, draw the sodium ion with no outer-shell electron and a 1⁺ charge, and the chloride ion with eight outer-shell electrons (the original seven crosses plus the transferred dot) and a 1⁻ charge. Use square brackets around each ion and include the charge outside the bracket. The diagram represents the electron transfer and the resulting ions, not the sharing of electrons. A strong answer earns marks for these points. Draw the outer-shell electrons of each atom using dots for one atom and crosses for the other. Show the transfer of one electron from the sodium atom to the chlorine atom. Draw the sodium ion with no outer-shell electrons and a 1⁺ charge. Draw the chloride ion with eight outer-shell electrons and a 1⁻ charge. A common slip: Drawing the ions without square brackets or charges. Instead, enclosing each ion in square brackets and writing the charge outside, such as [Na]⁺ and [Cl]⁻. Exam tip: Use dots for one atom and crosses for the other so the transferred electron is easy to track.
Key words
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Dot and cross diagram
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Square brackets
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Electron transfer
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Charges
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See every definition
- Dot and cross diagram
- A diagram that represents the electron transfer during the formation of an ionic compound, for example sodium chloride.
- Square brackets
- Used around each ion in the diagram, with the charge placed outside the bracket.
- Electron transfer
- The movement of an outer-shell electron from one atom to another, which the diagram represents rather than the sharing of electrons.
- Charges
- Shown outside the square brackets for each ion, such as a 1⁺ charge on the sodium ion and a 1⁻ charge on the chloride ion.
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