2 Chapter 6 • organising elements Organising elements

6
Properties and structure
Elements in our oceans
Fig 6.39 There are more
elements in our oceans
than you may think.
32 Chapter 6 • organising elements
We all know that water
has the formula H 2 O and
therefore contains oxygen and
hydrogen. Sea water contains
salt, so it also has the elements
sodium and chlorine. But did
you know that our oceans
contain a whole range of other
elements, such as magnesium,
sulfur, calcium, potassium,
bromine and even gold? So
how did the elements get into
the water that covers twothirds
of the surface of our
planet? And in what form are
these elements present within
the sea water?
Many of the metals present in
sea water have been leached
from minerals on the floor
of the ocean. Sodium is an
example of this; it dissolves
into the water in the form
of sodium ions (Na + ). Over
time, gases from volcanic
activity on Earth have passed
through the oceans. Some of
these gases, such as hydrogen
chloride, contain chlorine and
this element also becomes
dissolved in sea water in the
form of ions. Sulfur is also a
product of volcanic activity
and most sulfur in today’s
oceans exists in the form of
sulfate ions.
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