Electronegativity and bond polarity

Question 1

What is Electronegativity?

Answer 1

Electronegativity is the measure of the attractions of a bonded atom for the pair of electrons in a covalent bond.

Question 2

What changes when the bonded atoms are different elements?

Answer 2

• The nuclear charges are different
• The atoms may be different sizes
• The shared pair of electrons may be closer to one nucleus than the other.
• in molecules of the same elements, electrons are shared evenly

Question 3

How is Electronegativity measured?

Answer 3

• The Pauling scale has the Pauling electronegativity values and it can be used to compare E.N of elements
• Electronegativity depends of an element’s position in the periodic table
• Nuclear charge increases across the periodic table and Atomic Radius decreases as you go up the table - Atomic radius has a bigger influence that nuclear charge
• Nitrogen, Oxygen, Fluorine and Chlorine are the most EN

Question 4

How do Ionic bonds occur?

Answer 4

• When the EN difference is large, one bonded atom will have a much greater attraction and it will have gained control of the electrons

Question 5

Bond types and the Electronegativity difference:

Answer 5

• Covalent = 0
• Polar covalent = 0-1.8
• Ionic = >1.8

Question 6

Non-polar bonds

Answer 6

• In non polar bonds, electrons are shared equally.
• This happens when the bonded atoms are the same or if the bonded atoms have the same or similar EN
• Molecules of elements such as H2 where electrons are shared equally are called Pure Covalent bonds.
• Carbon and Hydrogen are a non-polar bond

Question 7

Polar bonds

Answer 7

• A bond will be polar when the bonded atoms are different and have different electronegativity values, resulting in a polar covalent bond
• A bond becomes polarised with one atom having a slightly positive charge and the other have a slightly negative charge
• This separation of opposite charges is called a dipole
• Dipole in polar covalent bonds are permanent

Question 8

Polar Molecules

Answer 8

• Multiple polar bonds may reinforce the polarity and make the molecule as a whole more polar - this happens in shapes with lone pairs
• Or they may oppose each other and cancel each other out thus becoming non polar