Calcium is the third element in group two on the periodic table. It’s really very
common. We find it all over the world in all sorts of minerals. So for example you can
have bones, this is a pelvis of a sheep, I found it when I was walking one day, you can
see the legs go in there and there.
In here we have some calcium turnings. We’re storing them in our glove box. This glove
box here is a contraption full of nitrogen, it’s dry nitrogen so that we can keep our
calcium away from oxygen and away from moisture as well, because obviously what we don’t
want is when we get our nice very reactive calcium surface we don’t want it to tarnish
from oxides too quickly before we can react it with things. So what we have here inside
the bottle are turnings of calcium. Calcium is quite hard compared to sort of the heavier
group two elements, so strontium and barium, so it’s harder to file.
Bones are made from calcium phosphate mixed with some organic material as well and they’re
very strong because of the structure within the bones. There are all sorts of shells of
molluscs and the like where they use calcium carbonate from the sea water, getting the
calcium out, reacting with carbon dioxide and making their shells. And because shells
are made out of calcium carbonate, which dissolves in acid, people are quite worried about the
effects of global warming. Not the heating up but when the C02 dissolves into the sea
it makes it more acid, so in principle shells could start dissolving and some molluscs may
not be able to survive because they just can’t make their shells.
If I just pour them out so you can see.
Calcium looks metallic than the calcium metal itself because of the way the electrons behave
in the solid. In fact it is because it is a very good electrical conductor but the compounds
are all white, because calcium has no free electrons that can go from one energy level
to another in the way you can say with copper. So copper sulphate is a beautiful blue colour,
calcium sulphate is white, and it’s actually colourless, so if you see a big crystal of
calcium sulphate it just looks like glass. But the white is caused by very small crystals
which scatter the light, just in the same way that any sort of white powder will scatter
light, flour for example or talcum powder, anything like that.
Calcium compounds themselves are actually mostly white, but calcium metal itself, as
you can see we’ve got tarnished parts but also there are some shiny bits where it’s
untarnished. So you’re actually seeing the metal the lustre of the metal there as well.
Calcium carbonate dissolves in water saturated with C02 to make calcium bicarbonate which
is more soluble. And so you can get water, so called hard water, that has quite high
levels of calcium. And when this percolates through the ground and comes to a cave it
can then crystallise out and you can get hanging down pillars of calcium carbonate, which are
called stalactites. And you can have pillars growing from the floor called stalagmites.
This is a stalagmite from Turkey. One of my friends called Hugh was really naughty. He
knew I was interested in minerals and he broke this off from a cave in Turkey about 45 years
ago and brought it and gave it to me so I was really pleased. And you can see the outside
looks quite blobby, and inside you can see there are nice crystals of calcium carbonate
because it has grown very, very slowly and so it can crystalise. And sometimes these
stalagmites and stalactites can grow really big. And more recently, in the last few years,
people have found huge crystals of calcium sulphate under the ground. Some of you may
have seen pictures of caves in Mexico where there are crystals big enough you can actually
walk along them. So there is no danger that calcium will ever run out, it’s the basis
of cements and concretes, or one of the bases because then you need other elements like
iron and silica to make the concrete itself, but calcium is one of the principle components.
We’re going to take calcium chloride, put it in a flame and do a flame test and see
if we can see the colour of the calcium in the flame. So as I said before about calcium
compounds, calcium compounds are often white, and here is a white calcium compound. So I’m
going to put it in the flame and see if we get any colour. Oh hello, that looks quite
red doesn’t it? Brick red is the classic calcium colour. Bit orangey to me, might be
a bit of sodium in there, or something like that. That was our calcium flame test.
The reason that you don’t find lumps of calcium metal lying around, the way you do
with copper or gold, is that metallic calcium is very reactive, reacts with water very quickly.
Magnesium doesn’t react because it has a layer of oxide on the surface, so surprisingly
magnesium is not nearly as reactive as calcium. You can use magnesium, or its alloys, for
the wheels on your car, go round really fast because they’re light. You couldn’t have
calcium wheels in your car, well you could, but the first time it rained your whole car
would go up in flames.
This again what we’ve got is our calcium chloride, hydrated calcium chloride. We’ve
got a bunch of it on this spatula. I’ll put it in the flame so that you can see that
it’s burning with a brick red flame which is characteristic of calcium. It’s kind
of a bit orangey to me as well actually, might be a bit of sodium or something in there.
Got anymore in there? A little bit.
Many people see calcium as a very English element, unlike strontium which was discovered
in Scotland, because of the white cliffs of Dover, the gateway for many people when they
first come to England. They’re made of calcium carbonate. And so this white colour of chalk
is very characteristic and all over the southern part of England you find large amounts of
chalk, which in the north of England they tend to be limestone, which is also calcium
carbonate but a slightly different variety of calcium carbonate so it’s a yellow or
honey colour because of the impurities of iron or some other element that’s in it.
Well you need calcium for all sorts of processes in the body and of course to build up your
bones. Particularly, say in the case of pregnant women, they need to have calcium for the bones
of the developing baby. But as people get older the calcium can come out of their bones
and make them very fragile, this is why elderly people sometimes break their hips and break
their bones so easily. So drinking milk and eating other sources of calcium are good because
it helps you replenish your bones and keep a reasonable level of calcium.