Electronegativity and Bonding

So what is electronegativity?
Besides being hard to spell, electronegativity is the ability of an atom to draw towards itself electron density in a chemical bond.  The scale used for electronegativity is unitless and all the numbers are relative.  However, it is related to electron affinity, somehow.  It doesn't say how in my notes.  Welp.  Also, Electronegativity increases left to right across a group, and increases from bottom to top in a period.  For example, F is the most electronegative while Fr is the least electronegative.

It turns out that you can classify bonds based on electronegativity difference of the bonded atoms!
If the difference is 0, then the bond is a covalent one.  If the difference is between 0 and 2, the bond is of the polar covalent variety.  A difference greater than 2 is an ionic bond.  So, in order of increasing difference of elctronegativity: Covalent (shares electrons) => Polar Covalent (partial transfer of electrons) => Ionic (tranfers electrons)


Now for practice, classify the following bonds as ionic, polar covalent, or covalent:

1. CsCl.
1. The electronegativity of Cs and Cl is 0.7 and 3.0 respectively.
2. 3.0 - 0.7 = 2.3
3. Ergo it is IONIC!
2. H2S
1. The electronegativity of H and S is 2.1 and 2.5 respectively.
2. 2.5 - 2.1 = 0.4
3. It is POLAR COVALENT!
3. NN
1. The electronegativity of N is 3.0
2. 3.0 - 3.0 = 0
3. SLYTHERIN!  COVALENT!