Transcript Ionization Energy, Electron Affinity, and Melting Points

Periodic Trends
Section 4.3
Ionization Energy
The amount of energy
needed to remove an outer
electron from a specific
atom or ion
Ionization Energy
The Trend
It decreases down a group
e- shielding - The reduction of
the attractive force between a +
nucleus and its outermost e- b/c
of the cancellation of some of the
+ charge by – charge of the
outer e-
Ionization Energy
Ionization energy increase
across a period
Adding e- to same level &
p+ can hold it tighter
Atomic Radius/Radii
Atomic radius
Usually determined for atoms
bonded or close together
Bond radius – ½ the distance
from center to center of two
like atoms bonded together
The Trend
Atomic radius increases as
you move down a group
Due to addition of principle E
level
The e- in the middle E levels
shield the outside e- from the
force of the nucleus.
Trend
Atomic radius decreases as you
move across a period
Decreases b/c of increased +
charge
–You are adding an e- and a p+,
but the e-’s are going into the
same E level and being pulled
by the p+
Atomic Radius
As charge increases, the
effective nuclear charge
increases also
This pulls e- closer to the
nucleus
Overall, this reduces the size
of the atom
Repulsive Forces
Eventually, the e- will get
close and repel each other
Here, the atom doesn’t get
any smaller
Similar trend for ionic radius
Atomic Radii
Electronegativity
Electronegativity – a measure of the
ability of an atom in a chemical
compound to attract e-’s
The higher the e-neg, the stronger
that atom will pull e-’s from other
elements
Electronegativity
Decreases as you go down a
group
Adding principle quantum #
+ nucleus can’t pull e- as much
b/c of e- shielding
E-neg
Increases across a pd.
Effective nuclear charge is
more of a factor
Electron Affinity
The energy emitted upon the
addition of an electron to a
neutral atom in the gas phase.
Becomes more negative
across a period
Decreases down a group
Similar to e-neg.
Melting and Boiling Point
Not as straight forward as
the other trends.
Change as the different
orbitals begin to fill