6.2 Electronegativity and Polarity

Question 1

What is covalent bonding? Required.

Answer 1

• The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 2

What is electronegativity? Required.

Answer 2

• The ability of a bonded atom to attract the bonding electrons in a covalent bond

Question 3

What is a Pauling electronegativity value?

Answer 3

• A value assigned as a measure of the relative attraction of a bonded atom for the pair of electrons in a covalent bond

Question 4

Where are electronegativity values the highest in the periodic table?

Answer 4

• Up a group
• Across (to the right of) a period
• (With the exception of group 0)

Question 5

Why do electronegativity values increase up a group?

Answer 5

• The atomic radius is smaller
• The bonded pairs of electrons are attracted more strongly to the nucleus of the atom

Question 6

Why do electronegativity values increase across a period?

Answer 6

• The nuclear charge increases
• This attracts the bonding pairs of electrons more strongly

Question 7

Which elements are the most electronegative?

Answer 7

• Fluorine
• Oxygen
• Nitrogen

Question 8

What is an ionic bond?

Answer 8

• An electrostatic attraction between positive and negative ions

Question 9

What is a non-polar bond, and what is it also known as?

Answer 9

• A bond where the electrons are shared equally between the bonded atoms
• A pure covalent bond

Question 10

What causes a bond to be non-polar? Give examples.

Answer 10

• The atoms have the same/ similar electronegativities, like carbon and hydrogen
• The atoms are the same, such as in diatomic molecules

Question 11

What is a polar bond? Give an example.

Answer 11

• A bond where the electron pair is shared unequally
• Hydrogen chloride

Question 12

What happens to atoms as a result of the existence of a polar bond?

Answer 12

• A permanent dipole is formed; there is a separation of opposite partial charges
• The pair of electrons sit closer to the atom with the higher electronegativity value, which causes the bond to be polarised as it has a small partial negative charge (δ-) on one side, and a small partial positive charge (δ+) on the other

Question 13

Why is the delta sign used to show dipoles?

Answer 13

• It shows that the charges are small

Question 14

How can electronegativity values be used to guess the type of bonding between atoms?

Answer 14

• If there is no difference in the electronegativity values of 2 bonded atoms, they will form a pure covalent bond
• A small difference creates a polar covalent bond
• If there is a large difference between the electronegativity values, one of the atoms will have a much greater attraction for the bonded pair of electrons, and would even take control of the electrons and form an ionic bond

Question 15

What makes molecules polar?

Answer 15

• If it is not symmetrical, the molecule may have an overall dipole as the dipoles wouldn’t cancel out

Question 16

How can you tell if a molecule is polar?

Answer 16

• If the dipoles act in opposing directions (think of them pointing from positive to negative), they cancel out and the molecule is non-polar
  (- If you were to pull at the dipoles around the central atom in its 3D structure, would it move? If the central atom would move, the molecule is polar.)

Question 17

Polar molecules only dissolve in what type of solvents? What about non-polar molecules?

Answer 17

• Polar solvents
• Non-polar molecules only dissolve in non-polar solvents

Question 18

How do ionic compounds (e.g. NaCl) dissolve in water?

Answer 18

• Water molecules attract and surround the Na+ and Cl- ions
• The ionic lattice breaks down as it dissolves
• Na+ ions are attracted to the oxygen of the water molecules (δ-)
• Cl- ions are attracted to the hydrogen of the water molecules (δ+)