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Matter
& atomic structure
Francine
Taylor-Campbell, Contributor
MAIN
POINTS
- Matter
consists of particles which may
be atoms, molecules or ions
-
Atom is the smallest part into which
an element can be divided
- An
atom consists of three main particles:
protons, neutrons and electrons
- Groups
of atoms can bond together to form
molecules
- Ions
are charged particles formed from
atoms or groups of atoms bonded
together
From
last week's lesson we learnt that
matter is all around us, whether in
the form of gases, liquids or solids.
This matter is made of particles with
an atom being the smallest part. An
atom has two main sections:
1.
A nucleus, which is the centre and
holds the protons and electrons.
2.
Shells which contain the electrons.
These
three sub-atomic particles have different
properties.
| PARTICLE |
RELATIVE
MASS |
RELATIVE
CHARGE |
| Proton |
1 |
+1 |
| Neuron |
1 |
Neutral |
| Electron |
1/1840 |
-1 |
Please
note that the overall charge on an
atom is zero (-1 + 1 = 0), hence,
atoms are uncharged. The mass of an
electron is 1/1840 of a proton. This
mass is very small, hence, we generally
say that the mass of an electron is
negligible or, it has no mass. This
is why the mass of an atom is derived
from the number of protons and neutrons.
Mass
number = Protons + Neutrons.
Remember
the masses given are not the actual
masses but the relative mass when
all three are compared. The relative
atomic mass (Ar) is the average mass
of one atom of an element compared
to the mass of one atom of carbon-12.
As
was stated earlier, the protons (P)
and neutrons (N) are in the nucleus
and this gives the nucleus a positive
charge, while the electrons are moving
in the shells with a negative charge.
In
an atom, the number of protons in
the nucleus is called the atomic number
and this is equal to the number of
electrons in the shells.
#
of protons = # of electrons This is
why the charges cancel out.
The
element oxygen, for example, is written
like this:
Mass
number = P + N = 16
Atomic
number = # protons = 8
Therefore,
the # neutrons = 16 - 8 = 8
In
a neutral atom # P = # E = 8
It
is important now for you to look at
the first 20 elements of the Periodic
Table. These elements are arranged
in order of increasing atomic number.
The first element is Hydrogen - 1
1H
Note
that hydrogen has 1 proton and, therefore,
1 electron, but since the mass number
= 1 (P + N), this means that H has
no neutrons.
All
the other elements can be written
in this form.
Please
review the symbols and atomic and
mass numbers of the first 20 elements.
Next week we will examine how the
electrons are arranged in the shells.
Francine
Taylor-Campbell teaches at Jamaica
College. Send questions and comments
to kerry-ann.hepburn@gleanerjm.com
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