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Elemental Notation
Each element has one or more atoms
associated with it. In each case, every atom of a particular element has the same
number of protons. However, a particular element may have several different types of
atoms, with different number of neutrons. As a result, each atom of a particular
element has the same atomic number, but a group of these atoms may have
several different mass numbers. The atomic number
represents the number of protons in the atom's nucleus, and it is this number that
determines the identity of the element. Because the protons are the charged
particles in the nucleus, the atomic number is also called the nuclear
charge. The mass number represents the total number of
protons and neutrons in an atoms nucleus.
Elemental Notation is a shorthand way of
writing information about a particular type of element, isotope or atom. An example
of the accepted form of elemental notation is shown below:
The large "X" represents where you will
find the atom's elemental symbol. The mass number, which is given
the symbol "A", is located in the upper left-hand corner. The atomic
number (also called nuclear charge), which is given the symbol "Z", is
found in the lower left-hand corner. |
Now, let's look at an
example of how this notation might actually appear.
Here we see a carbon atom with an atomic number of 6 (like all
carbon atoms) and a mass number of 12. Not all carbon atoms have a mass number of
12. You may have heard of carbon-14, which would have two more neutrons than this
carbon atom, accounting for the higher mass |
Although less common,
additional information may be located on the right side of the elemental notation, as
shown below:
This notation shows quite a bit of information. We know that
it represents a sample of calcium atoms, based on the elemental symbol "Ca".
The mass number, found in the upper left corner, is 40. The atomic number,
found in the lower left corner, is 20. The "+2", shown in the upper right
corner, represents the charge on the atoms of the sample. Here we see a group of
atoms which have lost two electrons each. The number "5", seen in the
lower right corner, represents the number of atoms in the sample. |
Isotopes are
atoms with the same atomic number, but different mass numbers. In other words,
isotopes have the same number of protons, but a different number of neutrons. The
three isotopes, or forms of hydrogen are shown below:
Here we see three atoms of hydrogen. Each atom of hydrogen
has one proton in its nucleus, so the atomic number of each is "1". The
mass number of each of these atoms varies. The hydrogen on the top has 2 neutrons in
addition to the 1 proton in the nucleus, for a total mass number of 3. The second
atom has 1 neutron in addition to the 1 proton in the nucleus, for a total mass number of
2. The bottom atom has no neutrons, only 1 proton in its nucleus, for a mass number
of one. A graphic representing the three isotopes of hydrogen is shown below.
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Now let us demonstrate how
you can tell the number of protons, neutrons and electrons in a particular atom by reading
the elemental notation.
| Elemental Symbol |
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# of Protons
(equal to Z) |
3 |
9 |
8 |
56 |
# of Neutrons
(equal to A-Z) |
4 |
10 |
8 |
80 |
# of electrons
(equal to Z modified by charge number) |
3 |
9 |
10 |
54 |
Please forward all questions, comments and criticisms to Gregory L. Curran.
© Copyright 2004 Fordham Preparatory School, All Rights Reserved.
Last Modified February 07, 2008 |
