2.2.2 - Bonding and structure Flashcards
The ‘dot-and-cross’ diagram of a molecule of PBr3 is given below. Name the shape of this molecule and explain why the molecule has this shape. (3)
- Pyramidal
- (Because there are) 3 bonded
pairs and 1 lone pair (around the
central phosphorus atom) - Electron pairs repel each other
as far apart as possible so will
take on a tetrahedral arrangement
(giving a pyramidal shape overall)
The displayed formula for propanoic acid is shown below. State the shape and bond angle around a carbon atom in the alkyl group of propanoic
acid. Explain the shape. (3)
- Tetrahedral
- 109.5(°)
- Four bonded pairs repel OR four bonds repel
State what is meant by the term ionic bond. (1)
- Electrostatic attraction between positive and negative ions
‘allow oppositely charged ions’
At room temperature and pressure, the first four members of the alkanes are all gases but the first four alcohols are all liquids. Explain this difference in terms of intermolecular forces. (2)
- Alcohols have hydrogen bonds
(and London forces) - Hydrogen bonds are stronger than London forces (in alkanes)
The boiling points of 2-methylpropan-1-ol and butan-1-ol are shown below.
2-methylpropan-1-ol = 108°C
butan-1-ol = 117°C
Explain why the boiling points are different. (2)
- 2-methylpropan-1-ol has less
surface (area of) contact / fewer points of contact - 2-methylpropan-1-ol has fewer /
weaker London forces so less energy required to break van der Waals’ forces in 2-methylpropan-1-ol
Compounds of calcium have many uses. Identify a compound of calcium that could be used to convert a soil pH from 5.8 to 7.5. (1)
- Ca(OH)2 (calcium hydroxide) / CO (calcium oxide)
What is the oxidation number of oxygen in F2O? Include the sign in your answer.
- +2
Solid chlorine and solid bromine have a similar structure. Name this structure. (1)
- Simple molecular lattice
The shape around the oxygen atom in butan-2-ol is non-linear. Predict the C−O−H bond angle and explain this shape. (4)
- 104.5°
- (oxygen atom) has two bond pairs
and two lone pairs - Bonded pairs / lone pairs / electron
pairs repel - Lone pairs repel more than
bonding pairs
Explain the differences in the melting points of phosphorus (P4) and chlorine (Cl2). (3)
- Phosphorus has more electrons
- Stronger London forces Stronger induced dipole(-dipole) interactions
- More energy required to break the intermolecular forces / bonds /London forces
The table shows the boiling points of ammonia, fluorine and bromine.
Ammonia, NH3 = -33°C
Fluorine, F2 = -188°C
Bromine, Br2 = 59°C
Explain the different boiling points of NH3, F2 and Br2. Include the names of any relevant forces and particles.
- NH3 has hydrogen bonding
- F2 and Br2 have London forces
- Forces / attractions are between
molecules / are intermolecular
for ammonia - Forces / attractions are between
molecules / are intermolecular
for fluorine and for bromine - The London forces in Br2
are greater than in F2 - Because bromine has more
electrons than fluorine - The London forces in Br2 are greater than hydrogen bonding in NH3
- Hydrogen bonding in NH3 is stronger than London forces in F2
Explain what is meant by the term electronegativity. (2)
- The ability of an atom to attract
electrons - (Electron pair) in a (covalent) bond
Explain why a CH2Cl2 molecule is polar. (1)
- The dipoles do not cancel out
- Because the molecule is non-symmetrical
Describe what is meant by the term ionic lattice, in terms of the type and arrangement of particles present. (2)
- Repeating pattern of oppositely charged ions
What is meant by the term covalent bond? (1)
- A shared pair of electrons
