Periodic Trends
Electronegativity/Electron Affinity (EN/EA):
measure of how much an atom wants to gain an electron
EN/EA Left
to Right across a Period: INCREASES (not including Noble Gases)
Why?
* Elements on the left side of the P.T. (metals) want to lose electrons. Elements on the right side of
the P.T. (nonmetals) want to gain
electrons. Trend does not include Noble
Gases because these
elements do not want to lose or gain
electrons.
EN/EA Top to
Bottom in a Group: DECREASES
Why?
* 
This interference (and resulting decreased “hold”) is referred to as the
SHIELDING EFFECT.
Ionization Energy (IE):
amount of energy required to remove an atom’s most loosely held electron
IE Left to
Right across a Period: INCREASES
Why?
* Elements on the left side of the P.T. (metals) want to lose electrons. Therefore, it will not require
much energy to remove an
electron. Elements on the right side of
the P.T. (nonmetals) want to gain
electrons. Consequently, a lot of energy will be needed
to remove (take away) an electron.
IE Top to
Bottom in a Group: DECREASES
Why?
*
Atomic
Radius (AR): distance from the nucleus to the H.O.E.L.
AR Top to Bottom in a Group: INCREASES
Why?
* There are more occupied energy levels as you move towards the
bottom of the P.T.
AR Left to
Right across a Period: DECREASES
Why?
*
Metallic Character:
how easily an atom will lose valence electrons (easier to lose = more
metallic = more reactive METAL)
Which metal loses its valence electron(s) most easily? Fr
Why?
* Francium has one valence electron. It
is more reactive than elements at the top of Group 1 because there are many
inner shell electrons that decrease the attraction the nucleus has for the
valence electrons.
Nonmetallic Character:
how easily an atom will gain electrons (easier to gain = more nonmetallic
= more reactive NONMETAL)
Which nonmetal gains electron(s) most easily? F
Why?
* Fluorine has seven valence electrons.
It is more reactive than elements at the bottom of Group 17 because
there are only a few inner shell electrons.
Consequently, the nucleus has a strong attraction for other electrons.