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.

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