chem bonding: covalent bonds

Question 1

what are covalent bonds?

Answer 1

electrostatic forces of attraction between positively charged nuclei and negatively charged shared electons

Question 2

what is a bond pair?

Answer 2

electrons involved in the formation of a covalent bond

Question 3

what is a lone pair?

Answer 3

electrons not involved in the formation of the covalent bond

Question 4

what is a dative covalent bond?

Answer 4

a special type of covalent bond in which only one of the bonded atoms contributes both of the shared pair of electrons

Question 5

conditions for dative covalent bonding to occur

Answer 5

1. one atom/molecule has a lone pair of electrons

2. the other atom/molecules has a vacant valance orbital

Question 6

what is bond length?

Answer 6

the optimum bonding distance

Question 7

what kind of overlap is in a sigma bond?

Answer 7

head-on overlap

Question 8

what kind of overlap is in a pi bond?

Answer 8

sideways overlap

Question 9

what bonds are in single, double and triple bonds?

Answer 9

single: sigma
double: sigma + pi
triple: sigma + 2 pi

Question 10

exceptions to the octet rule

Answer 10

1. nitrogen can have either 7 or 8 valence electrons
2. compounds of B and AlCl3 have less than 8 electrons in their valence shells
3. elements in period 3 and beyond can have more than 8 electrons in their valence shell

Question 11

factors affecting strength of covalent bonds

Answer 11

1. bond order
2. bond length
3. bond polarity

Question 12

how does bond order affect strength of covalent bonds

Answer 12

triple bond > double bond > single bond
in multiple bonds more sets of orbitals overlap and electrostatic forces of attraction between bonded electrons and nuclei of atoms is stronger, causing stronger covalent bonds

Question 13

how does bond length affect strength of covalent bonds?

Answer 13

shorter bond length = stronger covalent bonds
the npx orbital of 1 is smaller and less diffused than relative to the (n+1)px orbital of 2. the effective overlap is greater in H–1 than in H–2, resulting in higher bond energy and a stronger covalent bond

Question 14

how does bond polarity affect strength of covalent bond?

Answer 14

higher bond polarity = higher bond strength
in addition to existing covalent bonds, the 2 partial charges lead to increase in electrostatic attraction and hence greater bond strength

Question 15

how does strength of repulsion affect bond angle?

Answer 15

lp-lp repulsion > lp-bp repulsion > bp-bp repulsion

lp of electrons tend to push away the neighbouring bond pairs and force them closer together, causing bond angle to fall

Question 16

how does electronegativity affect bond angle?

Answer 16

the more electronegative the central atom, the greater the repulsion between bond pairs.
the more electronegative atom pulls bonded electron pairs closer to itself, forcing bond pairs closer to each other and with more repulsion, bond angle increases

Question 17

factors contributing to covalent character in ionic bond

Answer 17

1. high charge on cation
2. small size of cation
3. large size of anion

Question 18

why would an ionic bond possess covalent character?

Answer 18

when the cation polarises the anion and the electron cloud of the anion is distorted by the cation

Question 19

why would a covalent bond possess ionic character?

Answer 19

when two atoms have different electronegativities and the more electronegative atom has a greater share of the bonding electrons which cause a shift in electron density towards the more electronegative atom