Dative bonds & 10-electron species
Seven molecules and ions where a dative (coordinate) bond is the key to the dot-and-cross diagram. Pick a species, sketch it on paper, then reveal the worked answer. The dative pair is highlighted so you can see exactly where both electrons came from.
Your turn
Sketch the dot-and-cross diagram on paper, then reveal the worked answer.
Key points
What is a dative bond?
A dative (coordinate) bond is a covalent bond where both shared electrons come from the same atom. Once formed it is identical to any other covalent bond; the arrow only records where the pair came from.
How to spot one
Count the central atom's outer electrons. If it ends up forming more bonds than it has electrons to share, such as nitrogen with four bonds, one of those bonds must be dative.
Drawing the arrow
Point the arrow from the donor (the atom giving the lone pair) to the acceptor: N to H in NH4+, O to C in CO, N to O in the nitrogen oxides. Both electrons of that pair carry the donor's symbol.
Ions and charges
For an ion, draw the whole species in square brackets and put the overall charge outside, top-right. In an ionic solid such as CaSO4, each ion gets its own brackets and the metal ion has an empty outer shell.