State what is meant by the term exothermic.

The diagram below shows the electronic configuration of a sodium atom.

Draw on this

Which of these diagrams shows the electronic configuration of a fluorine atom?

• A: Two concentric circles around a central nucleus. The inner circle has 2 crosses, and the outer circle has 7 crosses (three pairs and a single cross).
• B: Two concentric circles around a central nucleus. The inner circle has 2 crosses, and the outer circle has 8 crosses (four pairs).
• C: Three concentric circles around a central nucleus. The inner circle has 2 crosses, the middle circle has 8 crosses (four pairs), and the outer circle has 7 crosses (three pairs and a single cross).
• D: Two concentric circles around a central nucleus. The inner circle has 2 crosses, and the outer circle has 6 crosses (three pairs).

Sodium ions and fluoride ions are formed when sodium reacts with fluorine.

The diagram below shows the electronic configuration and charge of a fluoride ion.

Draw on this

Which of these diagrams shows the electronic configuration and charge of a sodium ion?

• A: Inside square brackets with a $2+$ superscript: Two concentric circles, inner circle has 2 crosses, outer circle has 8 crosses.
• B: Inside square brackets with a $+$ superscript: Two concentric circles, inner circle has 2 crosses, outer circle has 8 crosses.
• C: Inside square brackets with a $+$ superscript: Three concentric circles, inner circle has 2 crosses, middle circle has 8 crosses, outer circle has 1 cross.
• D: Inside square brackets with a $-$ superscript: Two concentric circles, inner circle has 2 crosses, outer circle has 8 crosses.

Explain, in terms of its structure and bonding, why sodium fluoride has a high melting point.