The Atom and the Periodic Table
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Electron Cloud
Structure
Energy Levels
Rows on the
Periodic Table
Bohr Models
Electron Dot
Diagrams
Review
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The vertical columns in the periodic table
are called groups.
Elements in each group have similar
properties.
For example, in Group 11, copper, silver, and
gold have similar properties. Each is a shiny
metal and a good conductor of heat and
electricity.
What is responsible for the similar
properties?
Electron Cloud Structure
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Scientists have found that electrons within
the electron cloud have different amounts of
energy.
Scientists model the energy differences of
the electrons by placing the electrons in
energy levels as shown below.
Electron Cloud Structure
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Energy levels nearer the nucleus have lower
energy than those levels that are farther away.
Electrons fill these energy levels from the
inner levels (closer to nucleus) to the outer
levels (farther from nucleus).
Electron Cloud Structure
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Elements that are in the same group have the same number of
electrons in their outer energy level.
It is the number of electrons in the outer energy level that
determines the chemical properties of the element.
The electrons in the outer energy level are called valence
electrons.
The electrons available to the be lost, gained, or shared in the
formation of chemical compounds are referred to as valence
electrons.
These electrons are what determines an atom’s chemical
properties.
Energy Levels
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The energy levels are named using numbers
one to seven.
The maximum number of electrons that can
be contained in each of the first four
energy levels is shown below.
Rows on the Periodic Table
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Remember that the atomic number found on the
periodic table is equal to the number of electrons in
a neutral atom.
The first row has hydrogen with one electron and
helium with two electrons both in energy level one.
Energy level one can hold only two electrons.
Therefore, helium has a full or complete outer
energy level.
Rows on the Periodic Table
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The second row begins with lithium, which has three
electrons—two in energy level one and one in energy
level two.
Lithium is followed by beryllium with two outer
electrons, boron with three, and so on until you
reach neon with eight outer electrons.
Do you notice how the row in the periodic table
ends when an outer level is filled?
Bohr Models
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A Bohr model of the atom is a simplistic
representation using an element’s symbol as
the nucleus and circles to represent the
energy levels in the atom.
Dots are used to represent electrons in the
energy levels.
Remember, in reality, scientists cannot tell
exactly where an electron is at a given
moment or where it is going.
Bohr Models
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The picture shows a Bohr
model.
For simplicity, remember we
are going to use the
element’s symbol as the
nucleus.
In the picture, the nucleus
is too large.
Or, put another way, if the
nucleus were going to be
that large, the electrons
are too close.
If the picture were
accurate, we would have to
place the electrons about a
mile away.
Electron Dot Diagrams
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Remember elements that are in the same
group have the same number of electrons in
their outer energy level.
These outer electrons are so important in
determining the chemical properties of an
element that a special way to represent
them has been developed.
Electron Dot Diagrams
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An electron dot diagram uses the
symbol of the element and dots to
represent the electrons in the
outer energy level.
Electron dot diagrams are used
also to show how the electrons in
the outer energy level are bonded
when elements combine to form
compounds.
Electron Dot Diagrams
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To draw electron dot
diagrams, determine the
number of electrons in
the outer energy level.
Chlorine contains seven
electrons in its outer
energy level.
The element symbol is
written and dots are
placed around the symbol
to indicate the valence
electrons.
The element symbol
represents the nucleus
and the inner electrons.
Groups and Valence Electrons
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Notice in the figure that all the
elements in group 1 have the same
number of valence electrons thus,
their electron dot diagrams are
similar.
So generally speaking, the number of
valence electrons stays the same as
you go up or down a group.
This holds true for groups 1, 2, 13, 14,
15, 16, 17, and 18 (except for He).
Groups and Valence Electrons
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Group numbers are related to the number of
valence electrons for Groups 1, 2, 13-18.
These groups are referred to as the maingroup elements.
The figure at the right shows the elements of
Group 1. Notice they have one valence
electron.
Group 2 has two valence electrons.
For Groups 13-18, to determine the number of
valence electrons, subtract 10 from the group
number.
For example, Group 13 has three valence
electrons and Group 14 has four valence
electrons.
Color Your Own Periodic Table
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Be sure to include a
key to show which
color represents which
type of element
Label valence
electrons for groups
1 – 2 and 13 – 18.
Be sure it is neat!
1ve
2ve
Red – Nonmetals
Blue – Metals
Green - Metalloids
3ve 4ve 5ve 6ve 7ve
8ve