Structure and Bonding [1]: Atoms (A Level Chemistry)

Uploaded by freeeschool on 31.08.2012

A Level Biology: Structure and Bonding 1 - Atoms
Hi! Welcome to my first video on the series about Structures and Bonding. Today, we are
going to be looking at the structure of an atom.
You have probably heard the term “atom” before. If you broke down any material into
its smallest subunit, then an atom would be the smallest divisible unit that you can probably
break it into. But there are smaller subdivisions even in an atom and that’s what we are going
to discuss today.
The three major constituents of an atom are these three parts. You have the Electron,
Proton and the Neutron. The protons and neutrons are found within the nucleus of the atom and
the electron is a piece that whiz around the outside.
There is some other information on this slide telling you about each of these subunits.
A neutron has a neutral charge which means that it doesn’t have any charge at all.
A proton has a positive charge and an electron has a negative charge, and hence why the atom
is kept in check. The negative charges that make up the electron are balanced by the positive
charges of the proton. It actually holds the structure of the atom together. In fact, this
force holding them together is exceptionally large. It is the type of force that’s utilized
in a nuclear bomb.
You also got information about the mass of the different subunits. For instance, a neutron
has a mass of what we refer to as 1. A proton has a mass of 1 and an electron has a negligible
mass, so we refer to having no mass. That is summarized here on the table here telling
you the relative masses of each of these particles and the relative charges as well.
Now, if I just give you the example of Helium and you have probably seen in the Periodic
Table that you have these two numbers attached to each of the elements found within the Periodic
Table and that means something in relation to the amounts of protons, neutrons and electrons.
The top number to do with Helium or to do with any element found in the Periodic Table,
that’s your Mass number. The Mass number is the number of protons plus the number of
neutrons. That’s the symbol; they normally give a two-letter symbol. In some cases, it
can be a single letter or it can be three letters. Most are two letters and you know
if the same symbol is referring to the same element if it’s the lower case. He and the
“e” is lowercase, so that means that it is the same element. The bottom number which
is the proton number and this tells us the number of protons and it also tells us the
number of electrons. In this case, Helium, we know has 2 protons. It also has two electron
because remember that the proton number is usually the same as the electron and this
mass number tells us the number of protons plus the number of neutrons. Therefore, that
must be two. The number of neutrons must be two because 2 + 2 = 4.
We look at these examples and try to figure out how many protons, neutrons and electrons
in each. We take hydrogen first. H is the symbol for hydrogen. The atomic number of
the proton number down the bottom here, tells you that it has one proton. This top number
or the mass number tells us the number of protons plus the number of neutrons and so
if it already got one proton that must mean that it has no neutrons. Because the proton
number is also 1, the number of electrons is also one.
With Boron, which is B as the symbol for this, the number of protons is 5. The number of
electrons is also 5 and because the mass number is 11, we can tell that the number of neutrons
is six because 5 + 6 = 11.
Oxygen has 8 protons; also has 8 electrons and therefore has 8 neutrons because 8 + 8
= 16. Sodium or Na has a proton number of 11. So it has 11 protons, 11 electrons and
therefore, 12 neutrons. Chlorine has 17 protons, also has 17 electrons and therefore, 35 – 17
= 18 neutrons. Uranium has a symbol of U has 92 protons, 92 electrons and it has 146 neutrons.
What determines whether something is a hydrogen atom?
The determining factor for this is this value here. The atomic or the proton number is the
number of protons that is found within an atom that determines what type it is. For
instance, a hydrogen atom always has one proton. A boron atom always has 5 protons. An oxygen
always has 8, sodium 11, chlorine 17 and uranium 92. If you look up all of the elements in
the Periodic Table, it is the proton number that is the one that determines the type of
atom that it is.
The atoms are made up of protons, neutrons and electrons. The protons have a positive
charge. Neutrons have a neutral charge. An electron has a negative charge and the protons
and neutrons have a mass of one and the electrons, because they have negligible mass, we refer
to them as having no mass. Your mass number, how heavy an atom is, is the number of protons
plus the number of neutrons. The atomic or the proton number as it is sometimes called
is the number of protons and it also indicates the number of electrons and there are different
types of atom that you find on the Periodic Table. There are roughly 120 on the Period
Table at the moment and it is the number of protons that determine the type of atom that
he is.
[end of audio – 06:08] A Level Biology: Structure and Bonding 1 - Atoms