chemical bonding

Question 1

what is an ionic bond?

Answer 1

it is the strong electrostatic force of attraction between two oppositely charged ions, formed by the transfer of electrons between the original atoms.

Question 2

what is a covalent bond?

Answer 2

it is the strong electrostatic attraction between the positive nuclei of the two atoms and the bonding electrons shared between them.

Question 3

what is a dative bond?

Answer 3

it is a situation where both electrons come from the same atom.

Question 4

what is an adduct?

Answer 4

it is a chemical species containing two different similar species.

Question 5

what is a dimer?

Answer 5

it is a chemical species consisting of 2 identical simpler species.

Question 6

what is an expanded octet?

Answer 6

it is a case where the central atom has more than 8 valence electrons after bonding. it is only possible if the central atom has accessible vacant d orbitals. (period 3 onwards)

Question 7

what is the first postulate of the VSEPR theory?

Answer 7

the electrons in the valence shell of the central atom will experience the least repulsion when they are as far apart from each other as possible.

Question 8

what is the second postulate of the VSEPR theory?

Answer 8

the repulsion between electron pairs decrease in the following order: lplp repulsion > lpbp repulsion > bpbp repulsion

Question 9

2bp on central atom, shape and angle?

Answer 9

linear, 180

Question 10

3bp 0lp on central atom, shape and angle?

Answer 10

trigonal planar, 120

Question 11

2bp 1lp on central atom, shape and angle?

Answer 11

bent, <120

Question 12

4bp 0lp on central atom, shape and angle?

Answer 12

tetrahedral, 109.5

Question 13

3bp 1lp on central atom, shape and angle?

Answer 13

trigonal pyramidal, 107

Question 14

2bp 0lp on central atom, shape and angle?

Answer 14

bent, 104.5

Question 15

5bp 0lp on central atom, shape and angle?

Answer 15

trigonal bipyramidal, 90, 120

Question 16

4bp 1lp on central atom, shape and angle?

Answer 16

see saw, <90, <120

Question 17

3bp 2lp on central atom, shape and angle?

Answer 17

T-shaped, <90

Question 18

2bp 3lp on central atom, shape and angle?

Answer 18

linear, 180

Question 19

6bp 0lp on central atom, shape and angle?

Answer 19

octahedral, 90

Question 20

5bp 1lp on central atom, shape and angle?

Answer 20

square pyramidal, <90

Question 21

4bp 2lp on central atom, shape and angle?

Answer 21

square planar, 90

Question 22

what is the third postulate of the VSEPR theory?

Answer 22

repulsion between bond pairs of electrons increases with an increase in the electronegativity of the central atom and decreases with an increase in the electronegativity of the terminal atoms.

Question 23

how are sigma bonds formed?

Answer 23

it is formed by the head-on overlap between atomic orbitals. it usually occurs between s+s, p+p and s+p orbitals. it is symmetric about the bond axis.

Question 24

how are pi bonds formed?

Answer 24

it is formed by the sideways overlap of parallel p orbitals

Question 25

what bonds does a double bond contain?

Answer 25

it contains one sigma bond and one pi bond

Question 26

why is a sigma bond stronger than a pi bond?

Answer 26

this is because there is a greater extent of overlap between the atomic orbitals in a sigma bond.

Question 27

what is the covalent character in an ionic bond?

Answer 27

it arises due to the polarisation of an anion by a highly charged cation

Question 28

how is covalent character in an ionic bond determined?

Answer 28

it is determined by the polarising power of the cation. with a higher charge density, the cation can polarise the anion to a greater extent it is also determined by the polarisability of the anion. larger ions are more easily polarised.

Question 29

what is a non-polar bond?

Answer 29

it is where the bonded atoms have the same or similar electronegativities.

Question 30

what is a polar bond?

Answer 30

it is where one atom is more electronegative than the other. the atom which is more electronegative will carry a partial negative charge while the other atom will carry a partial positive charge.

Question 31

what is ionic character in a covalent bond?

Answer 31

the greater the difference in electronegativity between the two atoms, the more polar the covalent bond.

Question 32

what is bond energy?

Answer 32

it is the energy absorbed when one mole of a given covalent bond in a gaseous compound is broken into gaseous atoms or molecules.

Question 33

what affects covalent bond strength?

Answer 33

1. bond order: the greater the bond order, the greater the bond energy 2. size of the bonding atom: the smaller the atomic size, the less diffused the orbitals, the larger the extent of overlap between atomic orbitals, the stronger the covalent bond 3. electronegativity difference: the greater the electronegativity difference, the stronger the bond polarity and hence the greater the bond strength.

Question 34

what determines the polarity of a molecule?

Answer 34

it is determined by the overall net dipole moment of the molecules. this is determined by the bond polarities and the shape of the molecule.

Question 35

how does id-id interaction arise?

Answer 35

instantaneous dipole-induced dipole interaction arises due to instantaneous dipoles for non-polar molecules. electrons are mobile and they can be displaced towards one end of the molecule, making that end partially positive. the other end will then be temp. short of electrons and so becomes partially positive. it is present between all particles and the attraction is weak.

Question 36

what factors affect the strength of id-id interactions

Answer 36

size of electron cloud: a larger electron cloud is more polarisable and hence id-id interactions are more easily formed. surface area of contact between molecules: the greater the surface area of contact, the stronger the id-id interactions.

Question 37

how does pd-pd arise?

Answer 37

permanent dipole- permanent dipole attraction occurs between polar molecules due to the attraction between permanent dipoles in the structure. the strength of the pd-pd attraction increases with increasing overall dipole moment.

Question 38

how do hydrogen bonds arise?

Answer 38

it has to be bonded directly to very small, highly electronegative atom with lone pairs like F, O, N and the lone pairs of electrons in a neighbouring molecule can attract the partial positive charge on the H atom.

Question 39

arrange the strength of the bondings in ascending order.

Answer 39

id-id interaction < pd-pd attraction < hydrogen bonding

Question 40

what factors determine the strength of the hydrogen bond?

Answer 40

it depends on the extensiveness of hydrogen bonds (number of lones pairs of electrons and H atoms) and the polarity of the bond.