[6.2] electronegativity and polarity

Question 1

what is electronegativity?

Answer 1

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

Question 2

what is the effect of electronegativity on polarisation?

Answer 2

the greater the electronegativity difference between the two atoms in bond, the greater the polarisation of the bond

Question 3

how can you determine if a bond is non-polar, polar covalent, or ionic based on EN differences?

Answer 3

• non polar covalent bond: no different between EN
• polar covalent bond: small difference in EN
• ionic bond: large difference in EN

Question 4

what are the specific EN differences for different bond types?

Answer 4

• covalent = 0 EN difference
• polar covalent = 0 to 1.8 EN difference
• ionic = greater than 1.8 EN difference

Question 5

what is the scale that describes electronegativities?

Answer 5

• the pauling scale
  > eg. H has an EN of 2.1

Question 6

what 3 factors affect electronegativity?

Answer 6

• number of protons
• atomic radius
• shielding

Question 7

how does the number of protons affect electronegativity?

Answer 7

• negative electrons in the bonding pair are attracted to the positive nucleus
• the more protons, the stronger the attraction, so the higher the EN

Question 8

how does the atomic radius affect electronegativity?

Answer 8

• this is the distance from the nucleus to the outer electrons
• the close the bonding pair to the nucleus, the stronger the attraction, so the higher the EN

Question 9

how does shielding affect electronegativity?

Answer 9

• this is the repulsion of the bonding pair by electrons in inner shells between the nucleus and the bonding pair
• the more shells between the bonding pair and the nucleus, the weaker the attraction so the lower the EN

Question 10

what is the trend in electronegativity down a group?

Answer 10

decreases
> down a group there is:
- an increase in atomic radius
- more shielding
- weaker attraction between the bonding pair and the nucleus

Question 11

what is the trend in electronegativity across a period?

Answer 11

increases
> across a period there is:
- a decrease in atomic radius
- more protons so higher nuclear charge
- stronger attraction between the bonding pair and the nucleus

Question 12

what is a non-polar covalent bond?

Answer 12

• it happens when two atoms in a covalent bond have the same EN
• it means a covalent bond where the two electrons are shared equally
• eg. Cl-Cl bond

Question 13

what is a polar covalent bond?

Answer 13

• it happens when the two atoms in a covalent bond have different EN
• it means the two electrons are not shared equally
  > the more EN atom has a greater share of the two electrons and is δ- while the less EN atom has a lower share of electrons and is δ+
• eg. H-Cl bond where H is δ+ and Cl is δ-

Question 14

what is a bond dipole moment?

Answer 14

• bonds that are polar have this
• it is a measure of the strength and direction of the polarity in the bond
  > the bigger the difference in electronegativity, the bigger the bond dipole moment

Question 15

are C-H bonds polar or non-polar?

Answer 15

although there is a small difference in EN between the C and the H, C-H bonds in organic molecules are not regarded as being polar

Question 16

what are two types of non-polar molecules?

Answer 16

• ones with no polar bonds
• ones which contain polar bonds but all dipole moments cancel out (draw arrow and if they point outwards it cancels out)
  > eg. CO₂

Question 17

what is a polar molecule?

Answer 17

• one which contains polar bonds but all the dipole moments do not cancel out (if arrows point inwards)
  > eg. H₂O
• asymmetrical molecule