Structure and Bonding [2]: Electron Configuration (A Level Chemistry)


Uploaded by freeeschool on 31.08.2012

Transcript:
A Level Biology: Structure and Bonding 2 – Electron Configuration
Hi! Welcome to my second video on the series about Structure and Bonding. Today, we are
going to look at the Electron structure.
Today, we are going to look at how electrons are structured within the atom. We are going
to use the example of an atom of potassium. Looking at potassium, we can tell here because
it has a proton and an atomic number of 19, tells us that it has 19 protons. It also tells
us that it has 19 electrons and in this case, it has 20 neutrons because 20 + 19 = 39.
Now, electrons are arranged in sections called shells. One thing that I would tell you in
this video is probably relative to a GCSE qualification. In reality, it is much, much
more complicated than this, but for the purposes of your exam, for the purposes of your vision,
we will go with what is on the specification.
So this represents an atom of potassium. You can see in the middle here, it’s got a nucleus.
The nucleus contains the protons and the neutrons. They are the parts of the atoms that contain
the mass. Then you got these shells of electrons whizzing around the outside. The distance,
in reality, between the nucleus and the electrons is vast. A good equivalent might be easy is
you had a golf ball representing a nucleus and put it in the center spot of Wembley,
then the electrons would be whizzing around that side of the stadium.
The pattern for electrons structure within the shell is always the same. It is always
a maximum of two in the first shell, then a maximum of eight in the next and then eight
in the next and eight in the next. So this pattern rings true for all atoms found in
the Periodic Table.
In this case, there will be two in its first shell. There will be eight in its next shell
and there will be eight within third shell and then in the final shell, there would be
one left over. If we count up, nineteen electrons and that totals the number of electrons found within
potassium.
Mendeleev, whom we got at the top right here is a very, very important person in science
because he formulated the first Periodic Table and what he did was he began to put the different
elements into groups and into, basically, a pattern that we could try to understand.
The way in which he’s divided the Periodic Table is he divided it, first of all, into
two sections into groups which run down the table and periods which run across. Now, the
vertical columns which are groups indicate elements which have very similar properties
to one another. If it is in the same group, it has a very similar property to all elements
found within that group.
If we were to start with this element here, so this one is hydrogen and helium and work
our way across and then down and across, and keep going like this, then that pattern there
shows the ascending proton or atomic number. So they get slowly larger. Hydrogen has a
proton number of one, helium has two, lithium has three, beryllium has four, boron has five,
carbon has six and so on and so forth.
They are organized into ascending number or ascending proton number. Now, looking at groups
specifically, we can see how the groups are arranged on the Periodic Table. This section
here, that’s group 1. Starting with beryllium, magnesium and calcium here is group 2. Now
we jump to group 3 from here and so to boron. This is group 3 here up to group 8. You have
seen a labeled Periodic Table diagram and these are eight major groups.
This section in here is called the transition metals; we aren’t going to be dealing with
those today. But looking at the groups, we can all tell if it is specifically in Group
1, we can tell how many electrons it has on its outer shell. For example, if it is in
Group 1, it has one electron in its outer shell. If it is Group 2, two electrons. If
it is Group 3, three. If it is Group 4, four and so on and so forth. The group on the end
or Group 8 has a full outer shell and has eight electrons in its outer shell.
In summary, the electrons found within atoms are arranged in shells. The shells have a
capacity. The first shell has a maximum of two electrons, the second has eight, the third
shell has eight and the fourth shell has eight.
The groups run down the Periodic Table and so anything within a vertical group has very,
very similar properties to one another. For instance, lithium and sodium are very, very
similar in their properties.
The group number determines the number of electrons within its outer shell. An example
of this would be lithium being in Group 1; it has one in its outer shell. Magnesium,
being in Group 2, has two. Like aluminum being in Group 3, has three in its outer shell.
There are eight groups in total found in the Periodic Table.
[end of audio – 05:23] A Level Biology: Structure and Bonding 2 – Electron
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