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

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

Answer 8

• If there is a large difference between the electronegativity values of 2 bonded atoms, one of them will have a much greater attraction for the bonded pair of electrons
• The more electronegative atom can even take control of the electrons and form an ionic bond
  If the electronegativity difference is:
• 0, the bond will be covalent
• Between 0 and 1.8, the bond will be polar covalent
• Greater than 1.8, the bond will be ionic

Question 9

What is an ionic bond?

Answer 9

• An electrostatic attraction between positive and negative ions

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

What is a polar bond? Give an example.

Answer 12

• A bond where the electron pair is shared unequally
• A permanent dipole is formed; there is a separation of opposite partial charges
• Hydrogen chloride

Question 13

What is a polar bond like?

Answer 13

• 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
• The use of the delta sign shows that the charge is small

Question 14

What makes molecules polar?

Answer 14

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

Question 15

How can you tell if a molecule is polar?

Answer 15

• 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 16

Polar molecules only dissolve in what type of solvents?

Answer 16

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

Question 17

How do ionic compounds dissolve in water?

Answer 17

• 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+)