Here we’ll have a closer look at nonmetal oxides, and how they behave in water.
Metals
Nonmetals
Nonmetal
Oxides form
Acidic
Solutions
Nonmetal Oxides are oxides of elements on the right side of the staircase on the periodic
table. Remember, (click) nonmetal oxides react with water to form acidic solutions.
O
O
S
O
SO3
We’ll consider the nonmetal oxide sulphur trioxide, SO3. Nonmetals have
electronegativity values closer to that of oxygen than metals have.
O
O
S
O
not an
ionic
solid
So nonmetal oxides are not ionic solids like metal oxides are.
O
O
S
O
Covalent
Bonds
Instead the atoms are joined by covalent bonds, where electrons are shared.
O
O
O
S
O
O H
H
O S OH
O
H
SO3( l )  H 2O( l )  H 2SO4(aq)
At room temperature, SO3 is a liquid. When it dissolves in water,
O
O
O
S
O
O H
H
O S OH
O
H
SO3( l )  H 2O( l )  H 2SO4(aq )
It reacts with water, and through a series of reactions,
O
O
O
S
O
O H
H
H O S OH
O
SO3( l )  H 2O( l )  H 2SO4(aq)
Forms sulphuric acid, H2SO4. The Lewis structure for sulphuric acid is shown here. If you
check, you will see that sulphur, oxygen, and hydrogen atoms are conserved in this reaction.
O
H O S OH
O
H 2SO4
O H
H
H 2O
When H2SO4 is in water, (click) a molecule of H2SO4 will collide with a water
molecule and donate a proton to it,
O–
H O S OH O H
H
O

H 24SO4
HSO
+
H 2H
O3O
forming a hydrogen sulphate ion and a hydronium ion.
+
O
–
H O S O
O

HSO4
+
H O H
H
H 3O
+
Because hydronium ions are present, the solution will be acidic.
Makes
the
Solution
Acidic
Now we’ll look at a few equations we can write for nonmetal oxides reacting with
water.
Formula Equations for Reactions of
Nonmetal Oxides with Water
SO3( l )  H 2O( l )  H 2SO4(aq) sulphuric acid
SO2(g)  H 2O( l )  H 2SO3(aq) sulphurous acid
2NO2(g)  H 2O( l )  HNO3(aq)  HNO2(aq)
nitric acid
2Cl 2O(g)  H 2O( l )
P4O6(s)  6H 2O( l )
P4O10(s)  6H 2O( l )
nitrous acid
2HOCl (aq) hypochlorous acid
4H 3PO 3(aq) phosphorous acid
4H 3PO4(aq) phosphoric acid
When we are considering the reactions of nonmetal oxides with water, we usually stick to
writing formula equations for these reactions. We’ll look at some of the common ones here.
Formula Equations for Reactions of
Nonmetal Oxides with Water
SO3( l )  H 2O( l )  H 2SO4(aq) sulphuric acid
SO2(g)  H 2O( l )  H 2SO3(aq) sulphurous acid
2NO2(g)  H 2O( l )  HNO3(aq)  HNO2(aq)
nitric acid
2Cl 2O(g)  H 2O( l )
P4O6(s)  6H 2O( l )
P4O10(s)  6H 2O( l )
nitrous acid
2HOCl (aq) hypochlorous acid
4H 3PO 3(aq) phosphorous acid
4H 3PO4(aq) phosphoric acid
The formula equation summarizing the example we just went over is sulphur trioxide or SO3
reacts with water to produce H2SO4, sulphuric acid. Sulphuric acid is a strong acid.
Formula Equations for Reactions of
Nonmetal Oxides with Water
SO3( l )  H 2O( l )  H 2SO4(aq) sulphuric acid
SO2(g)  H 2O( l )  H 2SO3(aq) sulphurous acid
2NO2(g)  H 2O( l )  HNO3(aq)  HNO2(aq)
nitric acid
2Cl 2O(g)  H 2O( l )
P4O6(s)  6H 2O( l )
P4O10(s)  6H 2O( l )
nitrous acid
2HOCl (aq) hypochlorous acid
4H 3PO 3(aq) phosphorous acid
4H 3PO4(aq) phosphoric acid
The other common oxide of sulphur, sulphur dioxide, SO2, reacts with water to
produce H2SO3, or sulphurous acid. Sulphurous acid is a weak acid.
Formula Equations for Reactions of
Nonmetal Oxides with Water
SO3( l )  H 2O( l )  H 2SO4(aq) sulphuric acid
SO2(g)  H 2O( l )  H 2SO3(aq) sulphurous acid
2NO2(g)  H 2O( l )  HNO3(aq)  HNO2(aq)
nitric acid
2Cl 2O(g)  H 2O( l )
P4O6(s)  6H 2O( l )
P4O10(s)  6H 2O( l )
nitrous acid
2HOCl (aq) hypochlorous acid
4H 3PO 3(aq) phosphorous acid
4H 3PO4(aq) phosphoric acid
A common oxide of nitrogen is nitrogen dioxide, NO2. This reacts with
Formula Equations for Reactions of
Nonmetal Oxides with Water
SO3( l )  H 2O( l )  H 2SO4(aq) sulphuric acid
SO2(g)  H 2O( l )  H 2SO3(aq) sulphurous acid
2NO2(g)  H 2O( l )  HNO3(aq)  HNO2(aq)
nitric acid
2Cl 2O(g)  H 2O( l )
P4O6(s)  6H 2O( l )
P4O10(s)  6H 2O( l )
Water to produce both
nitrous acid
2HOCl (aq) hypochlorous acid
4H 3PO 3(aq) phosphorous acid
4H 3PO4(aq) phosphoric acid
Formula Equations for Reactions of
Nonmetal Oxides with Water
SO3( l )  H 2O( l )  H 2SO4(aq) sulphuric acid
SO2(g)  H 2O( l )  H 2SO3(aq) sulphurous acid
2NO2(g)  H 2O( l )  HNO3(aq)  HNO2(aq)
nitric acid
2Cl 2O(g)  H 2O( l )
P4O6(s)  6H 2O( l )
P4O10(s)  6H 2O( l )
nitrous acid
2HOCl (aq) hypochlorous acid
4H 3PO 3(aq) phosphorous acid
4H 3PO4(aq) phosphoric acid
Nitric acid, HNO3, which is a strong acid,
Formula Equations for Reactions of
Nonmetal Oxides with Water
SO3( l )  H 2O( l )  H 2SO4(aq) sulphuric acid
SO2(g)  H 2O( l )  H 2SO3(aq) sulphurous acid
2NO2(g)  H 2O( l )  HNO3(aq)  HNO2(aq)
nitric acid
2Cl 2O(g)  H 2O( l )
P4O6(s)  6H 2O( l )
P4O10(s)  6H 2O( l )
nitrous acid
2HOCl (aq) hypochlorous acid
4H 3PO 3(aq) phosphorous acid
4H 3PO4(aq) phosphoric acid
And nitrous acid, HNO2, which is a weak acid.
Formula Equations for Reactions of
Nonmetal Oxides with Water
SO3( l )  H 2O( l )  H 2SO4(aq) sulphuric acid
SO2(g)  H 2O( l )  H 2SO3(aq) sulphurous acid
2NO2(g)  H 2O( l )  HNO3(aq)  HNO2(aq)
nitric acid
Cl 2O(g)  H 2O( l )
P4O6(s)  6H 2O( l )
P4O10(s)  6H 2O( l )
nitrous acid
2HOCl (aq) hypochlorous acid
4H 3PO 3(aq) phosphorous acid
4H 3PO4(aq) phosphoric acid
An oxide of the nonmetal chlorine, Dichlorine monoxide, Cl2O, reacts with water to produce the weak acid
HOCl, hypochlorous acid. This is an equilibrium reaction. Oxides of the other halogens have similar
Formula Equations for Reactions of
Nonmetal Oxides with Water
SO3( l )  H 2O( l )  H 2SO4(aq) sulphuric acid
SO2(g)  H 2O( l )  H 2SO3(aq) sulphurous acid
2NO2(g)  H 2O( l )  HNO3(aq)  HNO2(aq)
nitric acid
nitrous acid
Cl 2O(g)  H 2O( l )
2HOCl (aq) hypochlorous acid
P4O6(s)  6H 2O( l )  4H 3PO3(aq) phosphorous acid
P4O10(s)  6H 2O( l )  4H 3PO4(aq) phosphoric acid
One of the common oxides of phosphorus, P4O6, reacts with water to produce the
weak acid H3PO3, phosphorous acid
Formula Equations for Reactions of
Nonmetal Oxides with Water
SO3( l )  H 2O( l )  H 2SO4(aq) sulphuric acid
SO2(g)  H 2O( l )  H 2SO3(aq) sulphurous acid
2NO2(g)  H 2O( l )  HNO3(aq)  HNO2(aq)
nitric acid
nitrous acid
Cl 2O(g)  H 2O( l )
2HOCl (aq) hypochlorous acid
P4O6(s)  6H 2O( l )  4H 3PO3(aq) phosphorous acid
P4O10(s)  6H 2O( l )  4H 3PO4(aq) phosphoric acid
Another oxide of phosphorus, P4O10, reacts with water to produce the weak acid
H3PO4, phosphoric acid
Formula Equations for Reactions of
Nonmetal Oxides with Water
SO3( l )  H 2O( l )  H 2SO4(aq) sulphuric acid
SO2(g)  H 2O( l )  H 2SO3(aq) sulphurous acid
2NO2(g)  H 2O( l )  HNO3(aq)  HNO2(aq)
nitric acid
nitrous acid
Cl 2O(g)  H 2O( l )
2HOCl (aq) hypochlorous acid
P4O6(s)  6H 2O( l )  4H 3PO3(aq) phosphorous acid
P4O10(s)  6H 2O( l )  4H 3PO4(aq) phosphoric acid
You should be familiar with these reactions, especially the reactions for the oxides
of sulphur and nitrogen.
Nonmetal
Oxides
Are also Called
Acidic
Anhydrides
You should also know that nonmetal oxides (click) are also called (click) acidic
anhydrides.
Nonmetal
Oxides
Are also Called
Acid
Anhydrides
Or simply “acid anhydrides”. It’s important to remember that nonmetal oxides, or
acid anhydrides react with water to produce acidic solutions.