chemical bonding l

Question 1

structure of ionic lattice

Answer 1

constituent ions are held in fixed positions in an ordely manner so that attraction is maximised and repulsion is minimised between oppositely charged ions

Question 2

describe ionic bonds

Answer 2

electrostatic attraction btwn cations and anions
non directional as an ion attracts an oppositely charged ion in all directions with no preferred orientation

Question 3

properties of ionic compounds

Answer 3

high melting/boiling point as strong ionic bonds need high amount of energy to break
soluble in polar solvent
insoluble in organic solvent

Question 4

why are ionic compounds electrical conductors in molten/aqueous state but not in the solid state

Answer 4

solid state: ions held in fixed positions and cannot act as mobile charge carriers
molten state: ionic lattice structure breaks down and ions are free to move and act as mobile charge carriers

Question 5

structure of diamond

Answer 5

each C atom is bonded to 4 other C atoms in a three dimensional lattice by forming strong covalent bonds

Question 6

structure of graphite

Answer 6

each C atom is bonded to 3 other C atoms in a layered structure by forming strong covalent bonds
weak intermolecular attraction between layers

Question 7

what is a metallic bond

Answer 7

electrostatic attraction between a lattice of positive ions and delocalised electrons
strong and non directional

Question 8

what are the factors affecting strength of metallic bond

Answer 8

1. number of valence electrons available: greater the number of valence electrons, the stronger the bonds
2. cahrge of cations: higher the charge of cations, the stronger the bonds
3. the size of cations: the smaller the cation, the higher the charge density, the greater the electrostatic attraction for the delocalised electrons and the stronger the bonds

Question 9

how can metals have high electrical conductivity even in the solid state

Answer 9

the delocalised electrons, not the cations, function as charge carriers and flow towards positive terminal

Question 10

how are metals malleable and ductile

Answer 10

a layer of positive ions can glide over another without breaking the metallic bond as metallic bonds are non-directional

Question 11

describe covalent bonds

Answer 11

electrostatic attraction between the shared pair of electrons and positively charged nuclei

Question 12

what and what are the conditions for a datice covalent bond

Answer 12

when the shared pair of electrons is provided by only one of the bonding atoms
one atom must have a lone pair of electrons for donation while the other atom must have a vacant low-lying orbital to accept the electron pair

Question 13

how to identify central atom in a dot and cross

Answer 13

less electronegative element and has more unpaired electrons

Question 14

how to identify side atoms in a dot and cross

Answer 14

more electronegative element and has fewer unpaired electrons
if H is present, it is always the side atom because it can only form 1 covalent bond

Question 15

why can some elements have more than 8 valence electrons

Answer 15

elements of period 3 and above have vacant, low-lying orbitals that are available for the expansion of octet

Question 16

rank of strength of repulsion

Answer 16

lp-lp > lp-bp > bp-bp

Question 17

why are electron pair arranged in their specific ways

Answer 17

to minimise interelectronic repulsion

Question 18

what is considered as one region of electron density

Answer 18

each lone pair
each lone electron
each single bond
each co-ordinate bond
each double bond
each triple bond

Question 19

define electronegativity

Answer 19

measures the relative tendency of its atom to attract its shared electron-pair in a covalent bond

Question 20

degree of polarity of a bond

Answer 20

the greater the difference in electronegativity between two atoms involved in a bond, the greater the bond dipole moment and the more polar is the bond

Question 21

how do instantaneous dipole induced dipoles arise

Answer 21

electrons constantly moving in any particle
at any moment, electron density can be unsymmetrical and forms instantaneous dipole
dipole can induce another dipole in neighbouring particle and cause attraction between them
dipoles are weak and short-lived

Question 22

how do the number of electrons affect strength of id-id interactions

Answer 22

more electrons, larger electron cloud size, electron cloud more easy to polarise, greater ease of formation of id-id, stronger id-id

Question 23

how does surface area for molecular interaction affect strength of id-id interactions

Answer 23

more branching present in isomers, lesser surface area for intermolecular interactions, weaker id-id formed
straight chained hydrocarbons would have strongest id-id

Question 24

how do permanent dipole-permanent dipole interactions aris

Answer 24

electrostatic attraction between partially positive end of one molecule and partially negative end of another molecule
present when there is a difference in electronegativity

Question 25

what affects pd-pd for molecules with a similar number of electrons

Answer 25

for molecules that have a similar number of electrons, the molecule which has a polar character forms stronger pd-pd as compared to non-polar molecule that forms weaker id-id

Question 26

how do hydrogen bonds arise

Answer 26

a hydrogen atom becomes highly partially positive as it is covalently bonded to the small and highly electronegative atom with lone electron pairs, which are either F, O or N

the highly partially positive hydrogen atom can form a strong intermolecular attraction with a lone pair of electrons on an adjacent molecule

since F, O and N are small, they allow the lone pair on the other F, O and N atom to come close to the protonic H atom

Question 27

the 2 critieria for hydrogen bonding

Answer 27

1. hydrogen atom covalently bonded to either F, O or N
2. lone pair of electrons on a F, O or N atom in a neighbouring molecule bearing a partially negative charge that can attract the partially positive charge on the H atom