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What does the Group
Number and Period
tell you about the Electrons of an Element?
Why is the Group Number of an Element important?
The group
number of an element in the periodic table
is the same as the
number of electrons in its outer shell.
An element in group
1 has 1 electron in its outer
shell.
An element in group 2
has 2 electrons in its outer
shell.
An element in group 7
has 7 electrons in its outer
shell.
An element in group 0
has a full
outer shell.
The number of electrons in the outer shell gives the
element
its
chemical
properties and controls its chemical
reactions.
Why is the Period of an Element
important?
The period
(row) in which an element is found
shows the
number of electron shells that it has.
The first period contains only hydrogen and helium.
Hydrogen and helium have only 1 electron shell.
The second period is from lithium to neon.
These elements have 2
electron shells.
The third period is from sodium
to argon.
These elements have 3
electron shells and so on.
What is the Electron Structure of an Element?
We can write the electron structure
of an element
according to the total number of electrons in its shells.
The inner shells are always full and have the numbers 2, 8, 8, 18.
For example, a potassium
atom has the
electron structure 2, 8, 8, 1.
Potassium is an alkali metal. See a picture
of a potassium atom.
It is in
group 1 (1
electron in its outer
shell) and period 4 (4
shells).
A chlorine atom has the electron
structure 2, 8,
7.
Chlorine is a halogen. See a picture
of a chlorine atom. Chlorine
is
in
group 7 (7 electrons in its
outer shell) and period 3
(3
shells).
The electron structure is also called the electronic structure,
the electron configuration or the
electronic configuration.
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