2. Trends across the periodic table
ïź Electronegativity increases from left to right
across the periodic table as the number of
valence electrons increase
ïź Electronegativity values decrease from the top to
the bottom in any group as the atomic radii
increases
ïź Metals are the least electronegative elements,
while non-metals are the most electronegative
4. Electronegativity gives an
indication of bond type
The bigger the difference in
electronegativity the more ionic
the bond is.
5. Electronegativity values can be
used to predict bond types
ïź A difference in electronegativity between two
atoms of >1.7 indicates that the bond is ionic
ïź A difference in electronegativity between two
atoms of <1.7 indicates that the bond is
covalent
ïź Polar Covalent: An uneven share of electrons.
Electronegativity difference of more than
zero but less than 1.7
6. 100% covalent compounds
ïź 100% covalent compounds have a
electronegativity value of zero.
ïź This generally only happens when they are
the same element. e.g. F and F
6
7. Bond Polarity and Electronegativity
Electronegativity and Bond Polarity
âą There is no sharp distinction between bonding types.
âą The positive end (or pole) in a polar bond is represented ÎŽ
+ and the negative pole ÎŽ-.
HyperChem
8. Example
ïź H and F
ïź Hydrogen has a electronegativity value of
2.1. Fluorine has a electronegativity of 4.0.
ïź The difference between them is 1.9
ïź => Ionic in character
9. Investigate the bond type
between the following atoms
ïź Which of the following compounds are ionic, fully covalent or polar
covalent?
H and F
H and S
H and N
C and O
H and H
Cl and Cl
Na and Br
Mg and O
K and F
H and H
How would you describe the bonding in the following compounds?
CaO, NH3, AlCl3 9