3.4 Magnesium oxide is a white solid with a high melting point.
Explain how the ions are held together in solid magnesium oxide.

When Magnesium reacts with Oxygen,

Magnesium gives up 2 electrons and oxygen takes those 2 electron. In this way they form an ionic bond and their outer shell also become full of electrons.

Now, The ions: Magnesium ion is Mg^2+ and Oxygen ion is O^2-

Note that the ions are opposite charged. As we know, opposite charges attract, they form a lattice where the ions are bonded with a strong ionic bond.

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