Atomic Structure (GCSE Chemistry)


Uploaded by freeeschool on 04.09.2012

Transcript:
GCSE Chemistry – Atomic Structure
Hello and welcome to a video about Atomic Structure. Today, we are going to learn how
to label atoms and then draw them from the information given in the Periodic Table.
It starts off with the Periodic Table. In the table, we have a list of all the elements
that we know about, along with those elements, we have some data that is given. What I would
like you to do is take out that data and draw any atom out of the first 20; that’s all
the way from Hydrogen up to Calcium, just by being given the data that is on the table
here.
To start off, we have to start quite simply and we have to be able to label the atoms.
Here’s an example of what an atom might look like; not drawn to scale. It starts off
with these structures right in the center. The green one here, I’m going to call Neutrons.
The red ones are Protons and they live in the structure in the center that we call the
Nucleus. This structure in the center is called the Nucleus and inside there, we have the
Protons and we have Neutrons.
Around the outside of the Nucleus, we have these green pathways and these blue structures
follow. The blue structures there are Electrons and the pathways that I mentioned there is called the “shell” or sometimes
called the “orbital” or sometimes called “energy level”. But I think “shell”
just for the sake of simplicity is the easiest one to remember.
So we have 5 labels that are very important for you to know and remember. It’s worth
spending a minute just to memorize that so that we could go on to the next part.
Here’s an example of an element that you might see on the Periodic Table. This is actually
Lithium and the numbers that you see associated with Lithium are 3 at the bottom and 7 at
the top. This part here is the symbol for the element. The number down here is the proton
number, sometimes called the atomic number. I’m going to refer to it as the proton number
for this video, just for the sake of simplicity. This number at the top is called the mass
number or sometimes called the atomic mass.
These numbers tell us different things about the atom. To work out how many protons, neutrons
and electrons to draw, we can very simply use these two to work it out. So the proton
number is very simple, it is the number at the bottom. To work out the number of neutrons,
you have the use the atomic mass. The atomic mass tells you the number of protons plus
the number of neutrons.
So if this is the number of protons plus neutrons, to work out the number of neutrons, this is
a simple case of subtracting the 3 from the 7. Subtract the number of protons away from
the number of protons and neutrons. To simplify all these in order to draw an atom, what we
can do is start off with just draw or write down on the left hand side, you can just write
the word “PEN”: Proton, Electron and Neutron. After that, it is a very simple case of plugging
in the numbers.
In terms of protons, that’s very easy. The proton number is the number at the bottom
here. We just plug that next to the P. Now the electron is always the same as the number
of protons for a stable atom. So we just bring that number down. This one here at the bottom,
the number of neutrons, while you can work that out just by taking away the protons from
the number of protons and neutrons, so that would just be a case of 7 – 3 = 4. So we
have 3 protons, 3 electrons and 4 neutrons.
Once we have done that, it is just a case of adding it to our diagram. So here is a
blank atom. I want to draw that with individual blocks which are right out for you, but this
is just a question of adding these numbers to this diagram.
So we know the protons are in the middle so we have 3 protons. We know that there are
4 neutrons and neutrons live again in the middle, in the nucleus. So we put 4 neutrons.
We have 3 electrons. If you remember from the last slide, the electrons live on the
shells. I will draw the electrons as little crosses in this case, 93 altogether.
The point to remember and a point to know at this stage, you can’t add more than two
electrons in the first shell. Only two will fill the first shell, so we fill up the first
shell with 2, we need one more so we can just put one more in there. Okay, this is what
an atom of Lithium looks like and that’s the method you use to draw it.
It is worth remembering it, as I said. The next one is the number of electrons in the
first shell is 2. The next shell is 8 and the next shell after that is 8 again. So it
might be worth here just practicing that. So why don’t you try and draw the atom for
Sodium.
Sodium goes like this: eleven down here and 23 at the top. Have a go and draw that and
see if you can come up with the right answer which I will show momentarily.
So here we go. The proton number is the number at the bottom; that’s 11. The electrons
is the same. Neutrons is 11 away from 23 which is 12. So very simply, 11 protons, 12 neutrons
and remember, electrons in the shells, so we have a total of 11 electrons. So we count
more than 2 in the first, more than 8 in the second and so we just put one in the final
shell there. There we have it, that’s an atom of sodium.
[end of audio- 6:30] GCSE Chemistry – Atomic Structure Page…
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