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Periodic Trends
The Periodic Law

The Periodic Law
states that the repeating chemical and
physical properties of elements change
periodically with the atomic numbers of
the elements.
What is a periodic trend?


Periodic trend…
properties of the elements change in a
predictable way as you move through
the periodic table
Atomic Radius

The textbook definition is:

Atomic radius is the distance from the
center of an atom’s nucleus to its
outermost electron.

I will show you a visual of the property.
Atomic Radius

Do you have an atomic radius graph?
If you turned yours in, does someone
near you have a graph that you can look
at?
Atomic Radius
Atomic Radius

What is the trend for the atomic radius
going down a group?

Do the data points generally show an
increasing pattern or a decreasing
pattern?
Atomic Radius

When you look at the atomic radius
graphs, what is the trend for atomic
radius across a period?

Do the data points generally show an
increasing pattern or a decreasing
pattern?
Atomic radius
• Atoms get smaller moving from the left
to the right across each period
• Why?
• Going from the left to the right across a
period, the atom’s outer electrons are
increasingly attracted to the nucleus
because they stay within the same
principal energy level.
Atomic Radius
Trend for atomic radius
• Atoms get larger going down a group
• Why?
• As you move down a group, the principal
quantum number of the outermost
electrons increases
Atomic Radius

http://www.shodor.org/chemviz/ionization/students/background.html
Atomic Radius –
Think of a Snowman

http://www.shodor.org/chemviz/ionization/students/background.html
Round 1

Larger Atomic Radius
• K or Cs
• K or Br
• C or Pb
Round 1

Smaller Atomic Radius
• Pb or Os
• Mg or Ar
• Ar or He
Ionization Energy (IE)



Ionization energy
this is the energy needed to remove one
of the atom’s outermost electrons.
Chemical Equation:
Li (g) ---> Li+ (g) + e–
IE = 8.64 X 10-19 J/atom
I will show you a visual of the property.
Ionization Energy

When you look at the ionization energy
graph, what is the trend for ionization
energy across a period?

Do the data points generally show an
increasing pattern or a decreasing
pattern?
Trend for IE

IE’s increase as you move from the left
to the right across a period.
• Why?
• The valence shell fills moving across a period,
so the number of electrons gets closer to a full
valence shell of 8 electrons. It becomes
harder and harder to remove an electron as
the valence shell fills.
Ionization Energy

What is the trend for ionization energy as
you move down a group?

Do the data points generally show an
increasing pattern or a decreasing
pattern?

Trend for IE
IE’s decrease as you move down a
group
• Why?
• The principal energy level increases moving
down a group, so the outermost electrons are
farther away from the pull of the nucleus.
Ionization Energy

http://www.shodor.org/chemviz/ionization/students/background.html
Round 1

Smaller Ionization Energy
• V or Ta
• Ta or Au
• Be or Sr
Round 1

Larger Ionization Energy
• I or Sr
• Pt or Ni
• Pt or At
Successive Ionization Energy

What do you think the term successive
ionization energy means?
Successive IE’s

The energy required to remove a second
electron from an atom is called its
second IE, and so on…
Ionization Energy

Do you think that it takes more or less
energy to remove a second or third
electron?

Take a look at the Ionization Energy
graph with both first and second
ionization energies plotted to answer this
question.
Successive Ionization Energies
Electronegativity

An atom’s electronegativity reflects its
ability to attract electrons in a chemical
bond.
• It is NOT an amount of energy
• It is NOT a property of an atom that can be
directly measured
Electronegativity
Electronegativity

The highest electronegativity values are
located in the upper-right hand corner of
the periodic table
• Fluorine has the highest electronegativity
value of 4.0

The lowest electronegativity values are
located in the lower-left hand corner of
the periodic table
Round 1

Smaller Electronegativity
• F or I
• Mn or Zn
• Hg or Zn
Round 1

Larger Electronegativity
• Bi or As
• Y or In
• Te or S
Enjoy Periodic Trends !!!