Dot and cross diagrams as a model for binary ionic substances
Dot and cross diagrams show the empirical formula/ratio of atoms to show how electrons are transferred
Ions are shown with full outer shells, square brackets, and a charge in the top right corner.
Ionic compounds are neutral overall, so positive and negative charge must balance.
When positive ions do not have the same magnitude of charge as negative ions, multiple of some ions will be required.

Keywords

Binary ionic substance - is made up of two different elements, one of which is a metal and the other a non-metal element.
Empirical formula - show the simplest whole number ratio of atoms of each element in a compound.
Ratio - can be used to determine the size of one quantity in relation to another.
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.
Magnitude - is the size of a quantity, for example the size of the charge on the ion.

Common misconception

The ionic bond is the transfer of electrons and not the electrostatic forces of attraction between the ions. Dot and cross diagrams show the empirical formula of the lattice and not an ionic molecule.

Ensure students have a good understanding of how ions are formed, the arrangement of ions in a giant lattice structure and empricial formula before moving on to disucss using dot and cross diagrams to model ionic bonding.

Use models to help students to make links between the 3D giant ionic structure and the dot and cross diagram model. Provide students with plenty of practice at drawing dot and cross diagrams, encourageing them to carefully check that they have drawn the correct number of dots adn crosses.

Teacher tip

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).

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6 Questions

Q1.

Magnesium is in Group 2 of the periodic table. Which of the following statements about magnesium ions are correct?

Correct answer: Magnesium atoms have two electrons in their outer shell.

Correct answer: Magnesium ions are more stable than magnesium atoms.

Magnesium ions have two electrons in their outer shell.

Magnesium atoms can be represented by the symbol Mg²⁺.

Q2.

Oxygen is a non-metal. What name is given to the type of ions that oxygen forms?

Correct Answer: anions, anion

Q3.

Which of the following symbols represents a sodium ion?

Correct answer: Na⁺

Na²⁺

Na⁻

Na²⁻

Q4.

True or false? Bromine atoms form stable Br⁻ ions.

Correct answer: true

false

Q5.

Neon is found in Group 0 of the periodic table. Why is neon unreactive?

Correct answer: Neon atoms do not need to lose or gain electrons to fill their outer shell.

Correct answer: Neon atoms are stable.

Neon atoms contain 0 electrons in their outer shell.

Correct answer: Neon atoms have a full outer shell of electrons.

Q6.

An element has atoms containing 20 electrons. Which of the following statements about the element are true?

Correct answer: The atoms of the element have 2 electrons in the outer shell.

Correct answer: The element forms ions with a charge of 2+.

The atoms of the element have 3 shells of electrons.

The element forms ions with a charge of 2-.

Correct answer: The atom is a metal.

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6 Questions

Q1.

Match the following terms to the correct definition.

Correct Answer:binary ionic substance,Made of two different elements, one a metal and one a non-metal.

Made of two different elements, one a metal and one a non-metal.

Correct Answer:magnitude,The size of a quantity.

The size of a quantity.

Correct Answer:dot-and-cross diagram,Used to show how chemical bonds are formed between atoms.

Used to show how chemical bonds are formed between atoms.

Correct Answer:empirical formula,Simplest whole number ratio of atoms of each element in a compound.

Simplest whole number ratio of atoms of each element in a compound.

Q2.

Aluminium atoms three electrons to form aluminium ions.

Correct Answer: lose, donate, give away

Q3.

Which of the following are binary ionic substances?

Correct answer: NaCl, sodium chloride

CuCO₃, copper carbonate

O₂, oxygen

Correct answer: AlF₃, aluminium fluoride

Q4.

This is a dot and cross diagram showing the bonding between sodium and chlorine. Which of the following statements about the image are correct.

Correct answer: The chlorine atom gained an electron to form an ion.

The sodium atom donated two electrons to the chloride ion.

Correct answer: Both ions have a full outer shell of electrons.

The ratio of sodium to chloride ions in the substance is 2 : 1.

Q5.

The formula for aluminium oxide is Al₂O₃. Which statements are correct?

Correct answer: The ratio of aluminium ions to oxygen ions is 2 : 3.

The ratio of aluminium ions to oxygen ions is 3 : 2.

Correct answer: The overall charge on aluminium oxide is neutral.

The charge on an aluminium is 3-.

Q6.

Lithium ions, Li⁺ and oxygen ions, O²⁻, form lithium oxide. What is the empirical formula for lithium oxide?

Correct answer: Li₂O

LiO₂

Li₂O₂

LiO