Drawing dot and cross diagrams for ionic compounds Revision Notes | GCSE Edexcel Higher Chemistry
In a dot and cross diagram for an ionic compound, electrons from the metal atom are shown as dots and electrons from the non-metal atom as crosses. Free notes.
Updated 22 Mar 2026 · Revise Right Team
Drawing dot and cross diagrams for ionic compounds is part of Chemical bonds, ionic, covalent and metallic in GCSE Edexcel Higher Chemistry.
3 min
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GCSE Edexcel Higher
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Content review
What this lesson covers
In a dot and cross diagram for an ionic compound, electrons from the metal atom are shown as dots and electrons from the non-metal atom as crosses. Free notes.
Draw dot and cross diagrams for ionic compounds formed between Group 1 metals and Group 7 non-metals
Draw dot and cross diagrams for ionic compounds formed between Group 2 metals and Group 6 non-metals
Explain how electron transfer creates ionic bonds using dot and cross notation
Apply the rules for drawing ionic compound diagrams to unfamiliar combinations
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Use this lesson to stay inside Chemical bonds, ionic, covalent and metallic while connecting the detail back to the wider Topic 1: Key concepts in chemistry topic.
Topic 1: Key concepts in chemistry
Chemical bonds, ionic, covalent and metallic
GCSE Edexcel Higher Chemistry
Revision notes
Read the core explanations from Drawing dot and cross diagrams for ionic compounds before testing yourself from memory.
1. Why Dot and Cross Diagrams Matter
When sodium metal meets chlorine gas, something dramatic happens - electrons jump from one atom to another. This creates charged particles that stick together with incredible force.
Dot and cross diagrams let you see exactly what's happening during this electron transfer. They're your window into the invisible world of ionic bonding - and examiners love testing them.
2. The Basics of Dot and Cross Diagrams
The rules are simple but crucial. Electrons from the first atom are shown as dots (•). Electrons from the second atom are shown as crosses (×). This lets you track which electrons came from where.
For ionic compounds, you draw the atoms before electron transfer, then show the ions after transfer. The key is showing how electrons move from metal to non-metal.
3. Drawing Sodium Chloride - The Classic Example
Worked example: Drawing the dot and cross diagram for sodium chloride
Draw a dot and cross diagram to show the formation of sodium chloride from sodium and chlorine atoms.
Na with 11 electrons: 2 in inner shell, 8 in middle shell, 1 in outer shell (shown as a dot) — Sodium is in Group 1, so has 1 electron in its outer shell
Cl with 17 electrons: 2 in inner shell, 8 in middle shell, 7 in outer shell (shown as crosses) — Chlorine is in Group 7, so has 7 electrons in its outer shell
Arrow showing the dot (Na's outer electron) moving to Cl's outer shell — The sodium electron transfers to complete chlorine's outer shell
Na⁺ (10 electrons, 2-8 arrangement) and Cl⁻ (18 electrons, 2-8-8 arrangement) — Both ions now have full outer shells and opposite charges
Answer: Na⁺ and Cl⁻ ions with the transferred electron clearly shown as a dot in Cl⁻'s outer shell
Notice how the sodium's single outer electron (dot) ends up in chlorine's outer shell. This gives chlorine a full outer shell of 8 electrons, while sodium is left with a full shell of 8 electrons too.
4. Group 1 and Group 2 Metals with Group 6 and Group 7 Non-metals
The pattern extends beyond sodium chloride. Group 1 metals always lose 1 electron. Group 2 metals always lose 2 electrons. Group 6 non-metals gain 2 electrons. Group 7 non-metals gain 1 electron.
This creates predictable formulas: Group 1 + Group 7 gives 1:1 compounds (like NaCl). Group 1 + Group 6 gives 2:1 compounds (like Na2O). Group 2 + Group 7 gives 1:2 compounds (like MgCl2). Group 2 + Group 6 gives 1:1 compounds (like MgO).
Worked example: Drawing magnesium chloride (MgCl₂)
Draw a dot and cross diagram for the formation of magnesium chloride.
1 Mg atom (Group 2) and 2 Cl atoms (Group 7) — Mg loses 2 electrons, each Cl gains 1, so need 2 Cl atoms
Mg with 12 electrons: 2-8-2 arrangement (outer electrons as dots) — Group 2 metals have 2 electrons in outer shell
Two Cl atoms, each with 17 electrons: 2-8-7 arrangement (outer electrons as crosses) — Need two chlorine atoms to accept Mg's two electrons
Two arrows: one dot goes to each Cl atom's outer shell — Each of Mg's outer electrons goes to a different Cl atom
Mg²⁺ (10 electrons, 2-8) and two Cl⁻ ions (18 electrons each, 2-8-8) — Mg²⁺ has 2+ charge, each Cl⁻ has 1- charge
Answer: One Mg²⁺ ion and two Cl⁻ ions, with the transferred electrons (dots) clearly shown in the Cl⁻ outer shells
5. Common Mistakes and Exam Technique
Students often struggle with electron counting and charge balancing. The most common errors involve forgetting to show the electron transfer clearly or mixing up which electrons belong to which atom.
In exam questions, you'll often be asked to 'show the electron transfer' or 'draw the formation of the ionic compound'. This means showing both the original atoms and the final ions with clear arrows indicating electron movement.
Exam tip: in ionic dot-and-cross diagrams, show only the outer electrons, use square brackets around each ion, and write the ion charge clearly outside the brackets., then link it to evidence, data, or an equation. A high-scoring GCSE answer names the particles involved, states what changes, and justifies the conclusion using correct scientific language. Where calculations are used, show each step with units and keep significant figures sensible. Finally, check that terminology matches AQA wording so your answer is unambiguous and mark-scheme friendly.
A good ionic dot-and-cross diagram shows what has happened to electrons after transfer. Sodium oxide is a useful extra example because each sodium atom loses one electron and the oxygen atom gains two electrons in total, giving two Na+ ions and one O2- ion. This helps students see why the formula is Na2O rather than NaO.
Sources and content standards
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-22.
How do you draw a dot and cross diagram for sodium chloride?
Draw the sodium atom (2-8-1) with its outer electron as a dot and the chlorine atom (2-8-7) with outer electrons as crosses. An arrow shows the dot moving to chlorine's outer shell, giving Na⁺ (2-8) and Cl⁻ (2-8-8) ions, both with full outer shells.
How do you draw a dot and cross diagram for sodium oxide?
In a dot and cross diagram for sodium oxide, each of two sodium atoms loses one electron and the oxygen atom gains two electrons in total. This gives two Na⁺ ions and one O²⁻ ion, which is why the formula is Na₂O.
What is a dot and cross diagram?
A dot and cross diagram is a visual representation showing the arrangement of electrons in atoms or ions, using dots for electrons from one atom and crosses for electrons from another. This shows which electrons came from where during electron transfer in ionic bonding.
How do you draw ionic bonds?
Ionic bonds are drawn by showing the metal and non-metal atoms before electron transfer, with arrows showing electrons moving from metal to non-metal. The ions formed are then drawn with full outer shells, in square brackets, with their charges shown outside.
How do you draw dot and cross diagrams for ionic compounds?
In a dot and cross diagram for an ionic compound, electrons from the metal atom are shown as dots and electrons from the non-metal atom as crosses. Only the outer electrons need to be shown, each ion goes in square brackets, and the ion charge is shown clearly outside.
Why is sodium oxide Na₂O and not NaO?
Sodium oxide is Na₂O because each sodium atom loses one electron, but the oxygen atom gains two electrons in total. So two sodium atoms are needed for each oxygen atom, giving two Na⁺ ions and one O²⁻ ion.
How do you draw a dot and cross diagram for magnesium chloride?
Magnesium chloride needs 1 Mg atom (2-8-2) and 2 Cl atoms (2-8-7), because magnesium loses 2 electrons and each chlorine gains 1. Each of magnesium's two outer electrons (dots) goes to a different Cl atom, giving one Mg²⁺ ion and two Cl⁻ ions.
How many electrons do Group 1, 2, 6 and 7 elements gain or lose?
Group 1 metals always lose 1 electron and Group 2 metals lose 2 electrons. Group 6 non-metals gain 2 electrons and Group 7 non-metals gain 1 electron. So Group 1 + Group 7 gives 1:1 compounds like NaCl, and Group 2 + Group 7 gives 1:2 compounds like MgCl₂.
Which dot and cross diagram correctly shows the formation of sodium chloride?
The correct dot and cross diagram for sodium chloride shows sodium's single outer electron (a dot) moving to chlorine's outer shell of 7 crosses. The ions formed are Na⁺ with a 2-8 arrangement and Cl⁻ with a 2-8-8 arrangement, with the transferred dot in the Cl⁻ outer shell.
Why are square brackets used in ionic dot and cross diagrams?
Square brackets are put around each ion in an ionic dot and cross diagram, with the ion charge shown clearly outside the brackets. This shows each ion on its own after electron transfer, such as [Na]⁺ and [Cl]⁻.
What are the electron arrangements of Na⁺ and Cl⁻?
Na⁺ has 10 electrons in a 2-8 arrangement and Cl⁻ has 18 electrons in a 2-8-8 arrangement. Both ions have full outer shells after sodium transfers its outer electron to chlorine.
What formula do Group 2 and Group 6 elements form?
Group 2 metals and Group 6 non-metals form 1:1 compounds, like MgO, because the Group 2 metal loses 2 electrons and the Group 6 non-metal gains 2 electrons. Group 1 and Group 6 form 2:1 compounds like Na₂O.
Why does magnesium chloride need two chlorine atoms?
Magnesium chloride needs two chlorine atoms because magnesium loses 2 electrons but each chlorine atom gains only 1. One Mg²⁺ ion and two Cl⁻ ions form, so the formula is MgCl₂.