intermolecular forces

Question 1

intra-molecular vs intermolecular

Answer 1

intra-molecular bonds is between atoms in a compound whereas intermolecular is between neighbouring molecules.

Question 2

types of intra-molecular bonds

Answer 2

1. covalent
2. ionic
3. metallic

Question 3

types of intermolecular bonds

Answer 3

1. induced dipole-dipole interactions (London dispersion forces)
2. permanent dipole-dipole interactions
3. hydrogen bonding

Question 4

permanent dipole-dipole

Answer 4

a weak attractive force between permanent dipoles in neighbouring polar molecules

H—Cl - - - - - H—Cl
δ+ δ- δ+ δ-

Question 5

how permanent dipole-dipole are formed

Answer 5

they are formed when there is a large difference in electronegativity between two atoms in a covalent bond. this causes the shared pair of e- to be shared unequally. they are pulled towards the electronegative atom as it has more e-

Question 6

electronegativity is…

Answer 6

the ability of an atom to attract the bonding electrons in a covalent bond

Question 7

induced dipole-dipole

Answer 7

a weak intermolecular forces that exist between all molecules, whether polar or non-polar. they act between induced dipoles in different molecules.

Question 8

how induced dipole-dipole are formed

Answer 8

• movement in electrons produces a changing dipole in a molecules
• at an instant an instantaneous dipole will exist, but this dipole will constantly shift and change
• the instantaneous dipole induces a dipole on a neighbouring molecule
• the induced dipole induces further dipoles on neighbouring molecules which then attract another one
• they are only temporary, in the next instant they may disappear but the process quickly repeats

Question 9

strength on induced dipole-dipole

Answer 9

the more e- in a molecule

• the larger the instantaneous and induced dipoles
• the greater the idd
• the stronger the attractive forces between molecules

Question 10

what affect does intermolecular forces have

Answer 10

they are largely responsible for physical properties e.g m/b points whereas covalent bonds determine the identity and chemical reactions of molecules

Question 11

hydrogen bonding

Answer 11

a special type of permanent dipole-dipole interaction found between molecules containing

• an electronegative atom with a lone pair of e-
• a hydrogen atom attached to an electronegative atom e.g H—O, H—N or H—F

Question 12

how/where does a hydrogen bond act

Answer 12

the bond acts between a lone pair of e- on an electronegative atom in one molecule and a hydrogen atom in a different molecule.
δ- δ+ δ+
:O: - - - - - - - - - - - - H H
/ \ \ /
H H :O:
δ+ δ+ δ-

Question 13

anomalous property of water- ice vs water density

Answer 13

ice is less dense than the water as h bonds hold liquid water molecules apart in an open lattice structure
- water molecules in ice are further apart than in water.

water is one of the few where the solid is less dense than the liquid. this means that ice floats on water instead of sinking forming an insulating layer and preventing water from freezing solid. the holes in the open lattice structure ( from water forming 4 H bonds that extend out and slightly apart) decrease the density. when it collapses, the molecules move back together.

Question 14

anomalous property of water- m/b point

Answer 14

water has a relatively high melting and boiling point due to lots of energy required to break the h bonds.

when the ice lattice breaks, the rigid arrangement of h bonds in ice is broken.

Question 15

anomalous property of water- surface tension and viscosity

Answer 15

water molecules held together by strong h bonds allows it to have a high surface tension allowing small, low force objects to float