2.2.2 Electronegativity and polarity

Question 1

when do polar bonds form

Answer 1

when 2 different atoms bond together it is likely their electronegativities will differ and so a polar bond with form

Question 2

define electronegativity

Answer 2

a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.

The most electronegative element is Fluorine then O then N

Question 3

is electronegativity in covalent or ionic bonds

Answer 3

• If the electronegativity difference is greater than 1.8 the bond will be ionic.
• between 0 and 1.8 the bond will be polar covalent
• equal to 0 the bond will be covalent

Question 4

explain electronegativity difference effect on the bond

Answer 4

If the electronegativity difference is large, one bonded atom will have a much greater attraction for the shared pair than the other bonded atom.
The more electronegative atom will have control of the electrons and at a large enough difference will become ionic.

Question 5

explain electronegativity patterns on the periodic table

Answer 5

Electronegativity decreases DOWN the groups (↓) and decreases from the right side of the periodic table to the left. (←)

Question 6

what is the scale used to measure electronegativity

Answer 6

the Linus Pauling scale

Question 7

explain the Pauling scale

Answer 7

• is used to measure electronegativity.
• Each element is assigned a number the higher the number (closer to 4) the more electronegative it is.
  eg. F = 3.98
  K = 0.82

Question 8

how are polar bonds drawn

Answer 8

we use 𝜹- or 𝜹+ representing dipoles
eg. O𝜹- - H𝜹+ becuase oxygen is more electronegative so attracts the electron more and therefore become slightly negative whilst the H becomes slightly positive.

the 𝜹-/+ would be in the top right like a charge

Question 9

how is it decided if a molecule is polar

Answer 9

depending on the shape of the molecule, the dipoles
- may reinforce each other to produce a larger dipole over the whole molecule
- or cancel out if the dipoles act in opposite directions

Question 10

when are diatomic molecules polar

Answer 10

in diatomic molecules if the bond is polar the molecule is polar

Question 11

when are polyatomic molecules polar

Answer 11

They are polar when the dipoles don’t cancel. eg. CH3Cl
They are non-polar when the molecule is symmetrical and the dipoles cancel. eg. CH4

Question 12

when is a molecule symmetrical

Answer 12

For a molecule to be symmetrical the shape must be one that has no lone pairs

Question 13

Explain why H₂O is/isnt polar

Answer 13

• H₂O is a polar molecule
• the 2 O-H bonds each have a permenant dipole and while they act in different directions these are not exactly opposite
• Overall the oxygen end of the molecule has a 𝛅- charge and the hydrogen end of the molecule has a 𝛅+ charge.

Question 14

Explain why CO₂ is/isnt polar

Answer 14

• CO₂ is non-polar
• the two C=O bonds each have a permenant dipole. The two dipoles act in opposite directions to each other.
• The dipoles cancel out and the overall dipole is zero