C6.2 Electronegativity And Polarity:

Question 1

Electronegativity definition

Answer 1

Attraction of a bonded atom for the pair of electrons in a covalent bond

Question 2

Pauling Electronegativity Values:

Answer 2

Across periodic table: nuclear charge increases and atomic radius decreases
Large Pauling Value = very electronegative element
Highest Pauling value = 4.0
Group 1 metals = least electronegative

Question 3

Ionic / Covalent =

Answer 3

Large electronegativity, one bonded atom has much greater attraction for shared atom, more electronegative atom has control over electrons and bond is ionic, not covalent

no. = electronegativity diff
0 = covalent
0 - 1.8 = polar covalent
1.8< = ionic

Question 4

non polar bonds

Answer 4

bonded electron pair shared equally between bonded atoms
non polar when:
- bonded atoms are same
-have same or similar electronegativity
bond is pure covalent bond

Question 5

polar bonds

Answer 5

bonded electron pair shared unequally between bonded atoms
bond is polar: bonded atoms are different and have diff electronegativity values, results in polar covalent bond

Question 6

eg polar bond
HCl

Answer 6

H = 2.1 Cl = 3.0
Cl is more electronegative
Cl has greater attraction for bonded pair of electrons than hydrogen, makes polar covalent bond
H-Cl polarised with small partial pos. Charge and partially neg. Charge on Cl atom
Permanent dipole is always in a polar covalent bond

Question 7

Polar molecules

Answer 7

eg. HCl = has permanent dipole bond acting in direction of H-Cl bond

depending on shape of molecule, the dipoles may reinforce one another, producing larger dipole, or cancelling out dipole if acts in opposite directions

dpeends on direction and shape of polar bonds and molecule

Question 8

polar molecules eg. H2O and CO2

Answer 8

H2O
- two O-H bonds have permanent dipoles
- two dipoles act in diff directions, not exactly oppose each other
- oxygen overall has delta - minus charge and hydrogen has delta positive charge

CO2
- two C=O bonds have permanent dipoles
- two dipoles act in diff directions and completely oppose each other
- dipoles cancel and overall dipole is 0

Question 9

Polar solvents

Answer 9

eg. NaCl dissolved in water
- water molecules attract na+ and cl- ions
- ionic lattice breaks down as dissolves
-in solution : water mol. surround na+ and cl- ions

Na+ ions attracted towards oxygen of water molecules
Cl- ions are attracted to hydrogen of water molecules