The links and activities on this page support
Science SOL 6.4
Matter
The student will investigate and understand
that all matter is made up of atoms.
Key concepts include
a) atoms are made up of electrons, protons, and neutrons;
b) atoms of any element are alike but are different from atoms of other elements;
c) elements may be represented by chemical symbols;
d) two or more atoms may be chemically combined;
e) compounds may be represented by chemical formulas;
f) chemical equations can be used to model chemical changes; and
g) a limited number of elements comprise the largest portion of the solid Earth, living matter, the oceans, and the atmosphere.
Standards of Learning Currently in Effect for Virginia Public Schools
Atomic Theory and the Periodic Table
The Periodic Table contains 4 key pieces of information for each
element:
1) the element's symbol,
2) the element's name,
3) the Atomic Number (the smaller number - an integer), and
4) the Atomic Mass (the larger number - an average atomic mass for the element).
The Atomic Number tells the number of protons in each atom of the
element.
The Atomic Mass is the average mass of an element's atoms. It tells the
number of protons and neutrons (since the mass of an electron is very
small compared to them).
To determine the number of neutrons in the atom, subtract the Atomic
Number from the Atomic Mass.
The charge on a proton is positive (+1), a neutron has a neutral (0)
charge, and an electron has a negative (-1) charge. The overall
charge of an element is neutral. So there are the same number of
electrons as protons.
| Subatomic
Particle |
Location |
Charge |
Mass
|
Proton
|
In the Nucleus of an atom
|
Positive (+1)
|
1 amu (atomic mass unit)
|
Neutron
|
In the Nucleus of an atom
|
Neutral (0)
|
1 amu
|
Electron
|
In the Electron Cloud around the
Nucleus
|
Negative (-1)
|
0 (about 0 compared to a proton
or a neutron)
|
For example, the element Iron appears in the Periodic Table like
this:
About 92 % of iron atoms have an Atomic Mass of 56 amu (atomic
mass units). From this information, Iron has 26 protons, 56 - 26 or 30
neutrons, and 26 electrons.
Elements are arranged in order by the Atomic Number. As you move from
left to right across a Period (a row), the Atomic Number
increases. Electrons are arranged in different "shells" or levels which
indicate where the electrons in an atom of the element are most likely
to be. The first level can hold up to 2 electrons, the second level
holds up to 8 electrons, the third level 18, the fourth level 32, the
fifth 32, the sixth 18, and the 7th 8. For any element, the
number of electrons in the Outer Shell (outermost level) is not over 8.
In the same Group or Family (a column), the number of outer electrons
is the same. This causes the elements in a family to behave in a
similar manner chemically.
Iron (our example) has 2 electrons in the first level, 8 in the
second, 14 in the third, and 2 in the outer shell. For purposes of the
our class, we will concentrate on the first three periods when
determining the arrangement of electrons.
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