Ionic Bonding
5 marks · EasyThis question is about ionic bonding in magnesium oxide and aluminium nitride.
Draw a dot-and-cross diagram to show the ionic bonding in magnesium oxide (MgO).
Include charges on the ions.
Aluminium is in Group 3 and nitrogen is in Group 5.
Using your answer to part (a) as a guide, describe how ions are formed when aluminium reacts with nitrogen to form aluminium nitride (AlN).
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) — · must show Magnesium ion (Mg^{2+}) with 8 electrons in outer shell, Oxygen ion (O^{2-}) with 8 electrons in outer shell, Two electrons shown transferred from Mg to O, Correct charges on ions
(b) Aluminium loses 3 electrons to form an Al^{3+} ion. Nitrogen gains 3 electrons to form an N^{3-} ion. Three electrons are transferred from each aluminium atom to each nitrogen atom. · must show Al loses 3 electrons to form Al^{3+}, N gains 3 electrons to form N^{3-}, Reference to transfer of electrons
Common mistakes: Missing charges on ions; Wrong number of electrons transferred
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Marking points
M1 (a) · 1 mark · Magnesium ion (Mg^{2+}) with correct number of electrons in outer shell (8)
M2 (a) · 1 mark · Oxygen ion (O^{2-}) with 8 electrons in its outer shell (2 crosses, 6 dots or vice versa)
A1 (a) · 1 mark · Correct charges shown on both ions (Mg^{2+} and O^{2-}) and two electrons shown as transferred
B1 (b) · 1 mark · Statement that aluminium loses 3 electrons to form Al^{3+}; nitrogen gains 3 electrons to form N^{3-}
B2 (b) · 1 mark · Describes electron transfer from aluminium to nitrogen (or equivalent description)
Worked solution
a) In magnesium oxide (MgO), magnesium loses two electrons to form a Mg^{2+} ion and oxygen gains two electrons to form an O^{2-} ion.
b) Aluminium (Al) is in Group 3 so it loses 3 electrons to form an Al^{3+} ion. Nitrogen (N) is in Group 5 so it gains 3 electrons to form an N^{3-} ion. Three electrons are transferred from aluminium to nitrogen.