Dot-and-cross diagrams

You need to be able to draw dot-and-cross diagrams to show the ions [ions: Electrically charged particles, formed when an atom or molecule gains or loses electrons. ] 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

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

Magnesium ions have the formula Mg²⁺, while oxide ions have the formula O^2-. You need to show one magnesium ion and one oxide ion.

Calcium chloride, CaCl₂

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.

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