intermolecular forces

Question 1

define intermolecular forces

Answer 1

amount of force between neighbouring molecules

Question 2

what are intermolecular forces caused by

Answer 2

weak attractive forces between small dipoles in different molecules

Question 3

what are the 3 types of intermolecular forces

Answer 3

permanent dipole dipole interactions
van der waals forces
hydrogen bonding

Question 4

define a permanent dipole dipole force

Answer 4

the weak attractive force between permanent dipoles in neighbouring polar molecules

Question 5

if you increase the number of electrons what does this do to the strength of the van der Waals forces

Answer 5

increased number of electrons = increased strength of van der Waals forces

Question 6

explain why electronegativity increases as you go to the right of the periodic table in terms of the size of the positive charge on the nucleus

Answer 6

number of protons increases
so increased positive charge increases
the increased attraction between the nucleus and the pair of electrons in the covalent bond
so elements on the right are more electronegative

Question 7

explain why electronegativity increases as you go to the right of the periodic table in terms of atomic radius

Answer 7

smaller atomic radius means the closer the bonding electrons will be to the nucleus of an atom
so elements on the right as more electronegative

Question 8

explain why electronegativity increases as you go to the right of the periodic table in terms of shielding

Answer 8

electrons in inner shells shield the electrons in the outer shells from the positive charge of the nucleus
so greater number of inner shells decreases electronegativity but as you go to the right in the same period it stays constant

Question 9

why do atoms with more electrons have a higher boiling point

Answer 9

more electrons = stronger van der waals forces

Question 10

what are van der waals forces caused by

Answer 10

the random movement of electrons
(every atom/molecule will experience van der waals forces)

Question 11

if you place one atom with van der Waals forces next to another atom what will it do

Answer 11

it will induce a dipole in atom 2 with the opposite facing charges therefore both atoms now experience van der Waals forces

Question 12

if you decrease electronegativity what happens to the strength of permanent dipole dipole forces

Answer 12

decrease electronegativity = decreased strength of permanent dipole-dipole forces

Question 13

to experience a permanent dipole dipole interaction what must both molecules have?

Answer 13

a permanent dipole

Question 14

what 2 conditions are needed for hydrogen bonding to take place

Answer 14

1. hydrogen atom bonded to a strongly electronegative atom
2. electronegative atom must have at least 1 lone pair of electrons

Question 15

what atoms can bond with hydrogen and undergo hydrogen bonding

Answer 15

fluorine
oxygen
nitrogen
(all 3 are very electronegative and have at least 1 lone pair)

Question 16

explain the bonding in hydrogen fluoride

Answer 16

fluorine has 3 lone pairs
and fluorine is the most electronegative atom so this strongly attracts the pair of electrons in the covalent bond so it is a polar molecule
hydrogen bonds form between the hydrogen on the right being attracted to the lone pairs of fluorine on the left molecule

Question 17

why is ice floating important for organisms living under water

Answer 17

insulates the water below preventing the water from freezing completely

Question 18

why does ice float

Answer 18

in ice the water molecules are further apart than in liquid water therefore it is less dense which allows it to float

Question 19

what do water molecules do at freezing point

Answer 19

arrange themselves into an ordered structure stabilised by a network of hydrogen bonds1

Question 20

in liquid water what happens in terms of hydrogen bonds

Answer 20

hydrogen bonds are constantly being being/formed due to the movement of water molecules

Question 21

why does water have a relatively high melting point

Answer 21

takes a lot of energy to break the hydrogen bonds

Question 22

iodine is non-polar what type of solvent does it dissolve in? what happens in terms of solvent molecules?

Answer 22

iodine non polar molecule so dissolves in a non polar solvent

solvent molecules move from van der Waals forces to the iodine molecules