Okay, well good evening everybody and welcome to the Department of Chemistry.
This lecture then we are looking at Group One of the periodic table. Now of
course everything around us is made up of the elements and there are many
elements, so here are a few elements. So we have for instance oxygen of course
aluminium, calcium. All these are common elements (carbon, nitrogen) but there are
many, many elements, we're going to be here quite some time at this rate. There's
over a hundred different elements. Here they all are in some rather random order.
Remember these make up everything around us, in some form or another.
How can we make sense of all these elements?
Well the first person that did this, that actually made some sense of the
different elements, was this chap.
Dmitri Mendeleev, a Russian and he first proposed the periodic table of the
elements and this is our starting point for today. We're going to be looking at
one family of elements within the periodic table or a group.
We're going to be looking at Group One. Now this is the red group, coloured here
We'll look at hydrogen at the start, then lithium, sodium, potassium, rubidium, and caesium. So
Mendeleev arranged all the elements in order of, well he arranged them in order of
increasing atomic weight, that's not quite how it should be but that's not
quite the real point of the periodic table, as we shall see shortly, but he
also, this was his key stroke of genius, arranged them into groups with
related properties and the groups are shown vertically like this. So this is
group 1, we have group 2 here. Another family with similar properties, group 3
or thirteen, fourteen, fifteen, sixteen, seventeen, eighteen. These ones are
the noble gases for instance, all of these are gases. So within each group
they have similar properties. We sort of skipped over these ones in the middle,
these are called the transition metals.
Ok, so these include things like iron, copper,
nickel and so on. These are common metals there in the transition metals and we
also glossed over these ones down the bottom there. They're sort of squeezed in
where you see those flashing symbols.
This would make the periodic table far too long, so usually they're cut out and
put at the bottom instead.
But we're going to focus on group one. Here they are group 1.
Now what do they have in common? This is the important point.
What all these things have in common? Well to understand this we need to look
at the atomic structure. So let's start off with the first atom, hydrogen. So
hydrogen consists of a proton and the proton is coloured red here.
The proton has a positive charge and this is balanced by the same number of
electrons. The electrons are shown in yellow.
So the electron is whizzing around the the nucleus. The nucleus is made up of
protons and neutrons. The hydrogen atom though doesn't usually have any neutrons. The
number of neutrons varies. Neutrons have no charge
but we can have different numbers in the same sort of atoms. So
we're really interested in the number of protons and electrons.
Now as we move across the periodic table from one element to the next, the number
of electrons and protons increases by one. We add one extra proton, positive
charge, in the nucleus and one extra electron to keep it neutral. So here we are,
this is helium.
We've got one extra electron. Now the next key point is that we start adding
electrons into different shells.
So for the next element lithium with three electrons in total it has just one
electron in its outermost shell, moving around as you see, moving around
far away from the central nucleus. But then we move across again we
add an extra proton, an extra electron. So beryllium here in group 2 has two
electrons in its outermost shell. Boron has three electrons in its outermost
shell. Carbon here has four. Nitrogen has five electrons. Oxygen has six electrons
in its outermost shell. Fluorine has seven electrons in its outermost shell.
There's 2 in the middle as well, so it's nine in total, but seven in the outermost
shell. Neon has eight in the outermost shell and that's full up now.
So now the next electron that we have
to add goes into a new shell and this is where we get back to sodium the next one
in Group 1.