Trends
in the periodic table
Periodic Table Trends
Like the previous slide shows (red
arrow), periodic table trends are
rarely perfect. There are often
elements that don’t conform to the
overall pattern or trend for one or
more reasons.
Metallic trend
• Most elements are metals.
• Non metals are on the far right of
the periodic table.
• Metalloids (stair step feature)
separate non metals from metals.
Atomic radii trend
In general…
• Atomic radii increases as you go
down a group (adding an energy
level).
• Atomic radii increases as you
move from right to left across a
period (decreasing effective
nuclear charge).
Keep in mind, atomic radii is calculated in different ways,
leading to slight variations depending on the source.
Ionic radii trend
In general…
• Ionic radii increases as you go down a
group (same as atomic radii).
• As you move from right to left across a
period, ionic radii is different…
Why does the ionic radii across a period
look this way?
• Atoms that become cations (+ ion):
lose valence electrons  lose an energy level  get smaller
• Atoms that become anions (- ion):
gain valence electrons  more repulsion between e-  get larger
First ionization energy trend
In general…
• Ionization decreases as you go
down a group.
• Ionization decreases as you move
from right to left across a period.
• Helium (and noble gases in
general) takes the most energy to
remove an electron from.
Electronegativity trend
In general…
• Electronegativity decreases as
you go down a group.
• Electronegativity decreases as
you move from right to left across
a period.
• Similar to ionization, except
fluorine is king here.
Melting Point trend
This trend isn’t as cut and dry as the
other trends, but there is some
repetition. Perhaps the following slide
sums it up best: this trend increases
toward the middle of a period. This is
certainly true for periods 2 (C) and 3 (Si),
and you could make the case for
subsequent periods with the metals in
the middle.