Periodic Properties
Chemical and physical
properties of the elements
change with their position
in the periodic table.
Review
• Group = column
• Period = row
• Octet Rule
– atoms tend to gain, lose, or share
electrons in order to gain 8 valence
electrons (full outer shell), like Noble
gases
– An element with a full valence shell is a happy
element 
Atomic Size
Distance from the center of
an atom's nucleus to the edge
of its electron cloud.
atom
Trend in Atomic Size
• Within a period, atoms generally
get smaller as you move from left
to right.
• WHY?
Because of the increasing
positive charge of the nucleus
draws the electrons in more
tightly.
Trend In Atomic Size
• Within a group, atoms generally
get larger as you move from top
to bottom.
• WHY?
Electrons are added to energy
levels further from the nucleus.
Dr. Lanzaflame; Atomic radii;
www.monroecc.edu/wusers/flanzafame/PerRadii.pdf
Ionization Energy
The amount of energy needed
to remove one valence
electron from an atom of an
element.
Trend in Ionization Energy
• Within a period, IE increases as
you move from left to right.
• WHY?
– As you move from left to right the number of
protons is increasing thus increasing the
coulombic attraction between the nucleus and
the electrons.
Trend In Ionization Energy
• Within a group, IE decreases as you
move from top to bottom.
• WHY?
– The farther away from the nucleus an electron
is, the easier it is to remove because the
coulombic attraction is less thus the positive
charge of the proton has less hold on the
negative charge of the electron.
Electronegativity
The ability to attract an
electron from another atom.
Trend in Electronegativity
• Within a period, EN increases as you
move from left to right.
• WHY?
–The number of protons is
increasing; therefore, the
coulombic attraction is
greater
Trend in Electronegativity
• Within a group, EN decreases as you
move from top to bottom.
• WHY?
–The atoms are larger due to
increased energy levels;
therefore, the attraction for
electrons would decrease
Reactivity
Reactivity refers to how likely an
atom is to react with other
substances.
Trends in Reactivity
• Metals
– Period - reactivity decreases as you go
from left to right across a period.
– Group - reactivity increases as you go
down a group
– Why?
• To react, metals needs to get rid of
electrons, thus they need a low IE.
Trends in Reactivity
• Non-metals
– Period - reactivity increases as you go
from the left to the right across a period.
– Group - reactivity decreases as you go
down the group.
– Why?
• For nonmetals to react, they must gain
electrons, so they need a high EN.