6.2 - Electronegativity and Polarity

Question 1

what is electronegativity?

Answer 1

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

Question 2

how is electronegativity measured?

Answer 2

Pauling scale

Question 3

what is the trend in electronegativity across a period?

Answer 3

electronegativity increases across a period

because nuclear charge increases and atomic radius decreases

Question 4

what is the trend in electronegativity down a group?

Answer 4

electronegativity decreases down a group.

Question 5

what happens if electronegativity difference is greater than 1.8?

Answer 5

the more electronegative atom will gain control of the electrons and the bond will be ionic rather than covalent.

Question 6

why is a C-H bond non-polar?

Answer 6

C and H atoms have very similar electronegativities.

Question 7

what is a polar bond?

Answer 7

a polar bond is where the bonded electron pair is shared unequally between the bonded atoms.

Question 8

what is it called when a molecule is polar due to differences in electronegativity?

Answer 8

a permanent dipole

Question 9

why is CO2 a non-polar molecule, even though C and O have different electronegativities?

Answer 9

The two C=O bonds each have a permanent dipole,
but the two dipoles act in opposite directions and EXACTLY oppose one another. (symmetrical)
So over the whole molecule, the dipoles cancel and the overall dipole is zero.

Question 10

how does water dissolve salt?

Answer 10

polar water molecule attract Na+ and Cl- ions.
ionic lattice breaks down as it dissolves.
water molecules surround the Na+ and Cl- ions.