1. Polarity

2. Electron Affinity
A measure of the tendency of an atom to accept an electron
Increases with increasing atomic number within a period
Decreases with increasing atomic number within a group

3. Electronegativity
Electronegativity – the relative ability of an atom to attract electrons in a chemical bond
Allows us to evaluate the electron affinity of specific atoms in a compound

4. Bond Character
A chemical bond between atoms of different elements is never completely ionic or covalent
Bond character depends on how strongly each of the bonded atoms attracts electrons

5. Polar Covalent Bonds
Results from unequal sharing of electrons in the bond
In a covalent bond, electrons spend more time near the nucleus of the atom with the higher electronegativity

6. Polarity
The atom that attracts electrons most strongly (has the highest electronegativity) has a slight negative charge
δ+ means partially positive
δ- means partially negative

7. Electronegativity Difference
Bond Character
Electronegativity Difference
Bond Character
> 1.7
Mostly ionic
0.4 – 1.7
Polar covalent
< 0.4
Mostly covalent
Nonpolar covalent

8. Determining bond character
Look at HF
Electronegativity of F = 3.98
Electronegativity of H = 2.20
Difference: = 1.78
Electrons move towards the fluorine atom

9. Polarity Polarity of molecules depends on Look at H2O and BeH2
The presence of polar bonds
The position(s) of polar bonds in the molecule (polarity is a vector quantity)
Look at H2O and BeH2
Element
Electronegativity
Hydrogen
2.20
Oxygen
3.44
Beryllium
1.57

10. Practice Determine if the following molecules are polar CH4 CH2Cl2
CCl4
CH3Cl
Element
Electronegativity
Carbon
2.55
Hydrogen
2.20
Chlorine
3.16

11. Nonpolar
Polar
Polar
Nonpolar
Polar