Chemistry Bonding Part III

Question 1

Simple covalent bonded molecules

Answer 1

• very low melting and boiling points
• interatomic molecules are strong
• intermolecular attractions are weak
• when they melt or boil, no covalent bonds are broken, always breaking intermoleculer forces

Question 2

intermoleculer

Answer 2

between molecules

Question 3

intramoleculer/interatomic

Answer 3

within molecules

Question 4

intermoleculer forces affect

Answer 4

physical properties

Question 5

three different types of intermolecular forces

Answer 5

• induced dipole-induced dipole (id-id) interactions
• permanent dipole-permanent dipole (pd-pd) interactions
• hydrogen bonding

Question 6

Van der Waals forces are commonly referred to

Answer 6

• id id

- pd-pd

Question 7

induced dipole-induced dipole/ Dispersion (london) forces

Answer 7

• electrostatic force of attraction between two temporary dipoles
• in atoms, polar and non-polar molecules
• weakest
• most significant between non-polar molecules and simple atoms

Question 8

Formation of ID-ID

Answer 8

• electron distribution in non-polar molecules are symmetrical on average but may be uneven at a particular instant in time
• momentarily polarised molecule has a temporary dipole which can induce a similar dipole in a neighboring molecule so that the molecules attract each other
• will be lost if the molecules move apart

Question 9

ID-ID in inert gases/monoatomic noble gases

Answer 9

• random fluctuations of the electron cloud may occur

Question 10

Factors affecting the strength of ID-ID

Answer 10

1. Size of electron cloud:
   - as the number of electron increases, the electron cloud is more polarisable (more easily distorted) and a temporary dipole is more easily induced-> stronger
   - down a group, electron cloud becomes more polarisable because the size of electron cloud increases, strength increases
2. Shape of molecule:
   - Straight chain molecules have a elongated electron cloud, branched molecules have a more spherical electron cloud
   - the same number of electrons, but elongated electron cloud would make contact with a neighbouring molecule over a greater surface area than a spherical one
   - straight chain molecules from stronger id-id

Question 11

Permanent dipole-permanent dipole (PD-PD) Interactions

Answer 11

• weaker than the intramolecular covalent bonds but generally stronger than id-id

Question 12

Formation of PD-PD

Answer 12

• permanent partial separation of charges -> polar molecules able to interact with one another -> positive end of one attracts the negative end of another

Question 13

Factors affecting strength of permanent dipole-permanent dipole

Answer 13

• depends on the polarity of the molecule
• greater electornegativity difference between the bonded atoms, the larger the bond dipoles (more polar molecule) the stronger the attraction between the oppositely charged dipoles

Question 14

Defintely polar bonds

Answer 14

G5,6,7

Question 15

Hydrogen bonding

Answer 15

• formed when hydrogen atom is covalently bonded to a very electronegative atom, it can form a hydrogen bond with another electornegative atom which has a lone pair of electrons
• the electrostatic force between the electron-deficient H atom and the very electronegative atom

Question 16

Factors affecting strength of hydrogen bonds

Answer 16

• the greater the electronegativity different between the H atom and the electronegative atom, the larger the bond dipoles (more polar) and the stronger the hydrogen bond

Question 17

Effects of hydrogen bonding on physical properties

Answer 17

• exceptionally high boiling and melting points (general trend of hydrides increase as they go down the group)
• solubility in water: many substances dissolve in water by forming hydrogen bonds with the water molecules
• dimerisation of molecules: