The atom, ionic bonding, covalent bonding and bonding properties

1. Electronegativity
The electronegativity of an element is a
measure of the power of attraction of
an atom for a shared pair of electrons
in a covalent bond

2. Trends across the periodic table
 Electronegativity increases from left to right
across the periodic table as the number of
valence electrons increase
 Electronegativity values decrease from the top to
the bottom in any group as the atomic radii
increases
 Metals are the least electronegative elements,
while non-metals are the most electronegative

3. Electronegativities of Elements
Electronegativity

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
 A difference in electronegativity between two
atoms of >1.7 indicates that the bond is ionic
 A difference in electronegativity between two
atoms of <1.7 indicates that the bond is
covalent
 Polar Covalent: An uneven share of electrons.
Electronegativity difference of more than
zero but less than 1.7

6. 100% covalent compounds
 100% covalent compounds have a
electronegativity value of zero.
 This generally only happens when they are
the same element. e.g. F and F
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7. Bond Polarity and Electronegativity
Electronegativity and Bond Polarity
• There is no sharp distinction between bonding types.
• The positive end (or pole) in a polar bond is represented δ
+ and the negative pole δ-.
HyperChem

8. Example
 H and F
 Hydrogen has a electronegativity value of
2.1. Fluorine has a electronegativity of 4.0.
 The difference between them is 1.9
 => Ionic in character

9. Investigate the bond type
between the following atoms
 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