Writing Chemical Formula Worksheet With Answer Key - Spes Unica Page 9
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28LI 6
5. COMPOUNDS CONTAINING COMPLEX IONS
E
Complex ions contain more than one kind of atom.
The table below contains some common complex ions
one positive
one negative
two negative
three negative
Ion
Formula
Ion
Formula
Ion
Formula
Ion
Formula
–
+
2–
3–
ammonium NH
ethanoate
CH
COO
carbonate
CO
phosphate
PO
4
3
3
4
–
2–
hydrogencarbonate
HCO
chromate
CrO
3
4
–
2–
hydrogensulphate
HSO
dichromate
Cr
O
4
2
7
–
2–
hydrogensulphite
HSO
sulphate
SO
3
4
–
2–
hydroxide
OH
sulphite
SO
3
–
nitrate
NO
3
–
permanganate
MnO
4
The valency of a complex ion is the same as the value of the charge of
the ion
+
e.g. NH
1 positive charge so valency = 1
4
2-
CO
2 negative charge so valency = 2
3
When writing chemical formulae with complex ions always put these ions
INSIDE A BRACKET.
+
e.g.
NH
becomes (NH
)
4
4
2-
CO
becomes (CO
)
3
3
3-
PO
becomes (PO
)
4
4
We can use the same cross valency method for writing chemical formulae
for compounds containing complex ions
9
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