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Question 15
Medium

Molecules can be shown using different diagrams or models.

The table shows a diagram and a model of water, H2O\text{H}_2\text{O}H2​O.

A table with two rows and three columns. Row 1 header: 'Molecule', 'Dot and cross diagram', '3-D space filling model'. Row 2 contains: Column 1: 'Water, H2O'. Column 2: 'A dot and cross diagram of a water molecule showing a central oxygen atom sharing electrons with two hydrogen atoms. There are two shared pairs containing a dot and a cross each, and two lone pairs of electrons (shown as dots) on the oxygen. Column 3: 'A 3D space-filling model of water, showing a red sphere in the middle for oxygen and two smaller white spheres for hydrogen at a bent angle.'

a.

Describe the advantages and limitations of these two different ways of showing a molecule of water.**

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[4]
b.

Dot and cross diagrams can also be used to show ionic compounds.**

Sodium fluoride, NaF\text{NaF}NaF, is an ionic compound.

  • The electronic structure of a sodium atom is 2.8.1.
  • The electronic structure of a fluorine atom is 2.7.

Two sets of empty brackets. The left set of brackets contains a central circle labeled 'Na' with two concentric outer circles for the electron shells of a sodium ion. The right set of brackets contains a central circle labeled 'F' with two concentric outer circles for the electron shells of a fluoride ion.

Complete the dot and cross diagram to show the ions in sodium fluoride.

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[2]
c.

Sodium fluoride is a solid at room temperature.**

Describe how particles are arranged in a solid.

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[2]
d.

Which statements about sodium fluoride are correct?**

Tick (✓\checkmark✓) two boxes.

[ ] Sodium fluoride has weak intermolecular forces. [ ] Sodium fluoride can conduct electricity in the solid state. [ ] Sodium fluoride contains metal and non-metal elements. [ ] Sodium fluoride is a salt formed from sodium hydroxide and hydrofluoric acid. [ ] Sodium fluoride has a low melting point.

[2]

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