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Ionic bonding

Dot-and-cross diagrams

You need to be able to draw dot-and-cross diagrams to show the ions [ion: Positively- or negatively-charged particles - eg positively charged hydrogen, sodium and potassium atoms. Ion charge helps determine a substance's acidity or alkalinity ] in some common ionic compounds [ionic compound: An ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron): The ions swap electrons to achieve a full outer shell. ].

Sodium chloride, NaCl

Diagram of bonding in sodium chloride. A sodium ion (2,8)+ gives an electron to a chloride ion (2,8,8)-. Both ions have full highest energy levels.

Sodium ions have the formula Na+, while chloride ions have the formula Cl-. You need to show one sodium ion and one chloride ion. In the exam, make sure the dots and crosses are clear, but do not worry about colouring them.

Magnesium oxide, MgO

Diagram of bonding in magnesium oxide. A magnesium ion (2,8)2+ gives two electrons to an oxide ion (2,8)2-. Both ions have full highest energy levels

Magnesium ions have the formula Mg2+, while oxide ions have the formula O2-. You need to show one magnesium ion and one oxide ion.

Calcium chloride, CaCl2

Diagram of bonding in calcium chloride. A calcium ion (2,8,8)2+ gives one electron to a chloride ion (2,8,8)- and another electron to another chloride ion (2,8,8)-. All three ions have full highest energy levels

Calcium ions have the formula Ca2+. Chloride ions have the formula Cl-.

You need to show two chloride ions, because two chloride ions are needed to balance the charge on a calcium ion.

Back to Structure and bonding index

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