bonding

Question 1

explain the VSEPR theory

Answer 1

pairs of outer electrons arrange themselves as far away from each other to minimise repulsion

Question 2

what is the name given to a molecule with 4 groups of electrons and what will the bond angle be?

eg CH4

Answer 2

tetrahedral

109.5

Question 3

what is the name + bond angle of a molecule with four groups of electrons, one being a lone pair?

eg - NH3

Answer 3

trigonal pydramidal

107

Question 4

water has four groups of electrons, 2 being lone pairs

name of shape and bond angle?

Answer 4

v shaped

104.5 because 2 lone pairs means more repulsion

Question 5

name + bond angle of a molecule with three groups of electrons + no lone pairs?

Answer 5

trigonal planar

120

Question 6

name and bond angle of a molecule where there are three groups of electrons and one lone pair?

Answer 6

bent / v-shaped

117.5

NOT THE SAME AS WATER BECAUSE WATER HAS 2 LONE PAIRS

Question 7

name and bond angle of a molecule with 2 groups of electrons

Answer 7

linear

180

Question 8

name and bond angle of molecule with five groups of electrons

Answer 8

trigonal bipyramidal

90 degrees on one side
120 on other

Question 9

name and bond angle of molecule with 6 groups of electrons?

Answer 9

octahedral

90

Question 10

list three types of IMF in ascending order of strength

Answer 10

van der waals
dipole - dipole
hydrogen

Question 11

where can dipole dipole forces occur?

Answer 11

between molecules with permanent dipoles
molecules with polar bonds

the delta + and delta - regions attract each other to form a lattice structure

Question 12

why does CO2 not have a dipole moment when it has more than one polar bond?

Answer 12

linear molecule so dipoles cancel out

Question 13

why do vdW occur between all molecules?

Answer 13

all atoms/molecules positive and negative charges so are NEUTRAL overall

however they produce weak electrostatic attractions

Question 14

helium has 2 protons and 2 neutrons and is neutral overall,

how can it have a permanent dipole?

Answer 14

at any one time, the electrons could be anywhere
the DISTRIBUTION OF CHARGE is changing at EVERY INSTANT
this means the atom has a dipole at THAT MOMENT

Question 15

how does an induced dipole occur?

Answer 15

the temporary dipole in one atom then affects the distribution of electrons in nearby atoms to form an induced dipole

this atom is then attracted to the original atom for THAT INSTANT

Question 16

what would create a larger instantaneous dipole?

Answer 16

more electrons

Question 17

what does the strength of vdW depend on?

Answer 17

Mr - more electrons and so more IM forces

SHAPE - straight chain molecules have more vdW as they can pack more closely together than branched molecules

Question 18

what are the conditions required for hydrogen bonding?

Answer 18

a very electronegative atom with a lone pair of electrons covalently bonded to a H atom

(OH or NH group)

Question 19

why is hydrogen bonding so strong?

Answer 19

Oxygen atoms in water have lone pairs of electrons

Hydrogen atoms are very electron deficient

so…. lone pair of O on one H2O atom is strongly attracted to electron deficient H atom

Question 20

when do H bonds form?

Answer 20

• when H is covalently bonded to electronegative atom (O or N)
• the H = + charged to form a bond with lone pair from O or N
• angle between OH/NH and H bond must be 180

Question 21

what is a simple molecular structure?

Answer 21

composed of small molecules (covalent bonding between atoms)

forces of attraction between molecules are much weaker (IMF)

Question 22

what is a macromolecular structure?

Answer 22

large number of atoms are linked in a regular 3D arrangement by covalent bonds

DIAMOND AND SILICON DIOXIDE

Question 23

what is a giant ionic structure?

Answer 23

lattice of positive electrons each surrounded in a regular arrangement by negative ions

Question 24

what is a metallic structure?

Answer 24

regular lattice of positively charged metal ions held together by a sea of delocalised electrons

Question 25

how can mpt/bpt tell us about the type of structure?

Answer 25

simple molecular compounds = low (all molecular compounds = covalently bonded)

giant structures = high