bonds exam questions Flashcards
the C-Br bond is polar. explain why CBr4 is not a polar molecule
CBr4 is a symmetrical molecule. therefore there is no net dipole moment
suggest in terms of the IMF for each compound, why CBr4 has a higher boiling point than CHBr3
despite CHBr3 having dipole-dipole forces, the larger the Mr for CBr4 means its van der waals forces are significantly stronger, so it has a higher boiling point
Which molecule is not able to form a co-ordinate bond with another species?
A BH3
B CH4
C NH3
D H2O
B CH4
Which species has a square planar shape?
A NH4+
B SF4
C XeF4
D PCl4+
Q2. C
Which bond has the most unsymmetrical electron distribution?
A H–O
B H–S
C H–N
D H–P
(Total 1 mark)
Q3. A
Which statement about inorganic ionic compounds is always correct?
A They dissolve in water to give neutral solutions.
B They release energy when they melt.
C They contain metal cations.
D They form giant structures.
Q4.
D
Which species has a lone pair of electrons on the central atom?
A CO2
B SO2
C PCl6‒
D SO42–
B
In which substance do covalent bonds break when it melts?
A hexane
B ice
C iodine
D silicon dioxide
(Total 1 mark)
Q6.
D
In which molecule are all the atoms in the same plane?
A CH3CHO
B CH3NH2
C C6H5Cl
D C6H5CH3
Q7.
C
Which molecule has a permanent dipole?
A BF3
B NH3
C SiCl4
D SO3
Q8.
B
Which substance contains delocalised electrons?
A cyclohexane
B graphite
C iodine
D sodium chloride
(Total 1 mark)
B graphite
Which species contains bonds that have different polarities?
A NH4+
B CCl4
C CH3Cl
D H3O+
C
CH3Cl
Which compound has hydrogen bonding?
A NaH
B NH3
C HI
D SiH4
B
NH3
Which compound contains a co-ordinate bond?
A HF
B NH3
C CHCl3
D NH4Cl
(Total 1 mark)
D
NH4Cl
Which molecule has a permanent dipole?
A CF4
B PCl5
C CO2
D Cl2O
D
Cl20
Which has a bond angle of 109.5°?
A C (diamond)
B C (graphite)
C NH2–
D NH3
A
Which substance has delocalised electrons?
A graphite
B iodine
C sodium chloride
D tetrachloromethane
A
Which species is not pyramidal in shape?
A PF3 B H3O+ C CH3– D BF3
D
BF3
Which change occurs when water is vaporised?
A An exothermic change occurs.
B Covalent bonds are broken.
C Intermolecular forces are overcome.
D The total energy of the molecules decreases.
c
Which compound has the highest boiling point?
A CH3CH2CH2Br
B CH3CH2CH2F
C CH3CH2CHO
D CH3CH2COOH
D
Which is not responsible for conduction of electricity?
A The sodium ions in molten sodium chloride
B The electrons between layers of carbon atoms in
graphite
C The bonding electrons in a metal
D The lone pair electrons on water molecules
D
Which row shows the bonding in ammonium chloride?
Covalent Dative Ionic covalent
A✔✘✘ B✔✔✘ C✔✔✔ D✘✘✔
C
Which molecule does not have a permanent dipole?
A CH3Br
B CH2Br2
C CHBr3
D CBr4
D
Which compound has the highest boiling point?
A butanal
B butan-2-ol
C but-2-ene
D 1-fluorobutane
B
Which species has a shape that is influenced by the presence of one or more lone pairs of electrons around the central atom?
A AlCl3-
B ClF3
C IF6+
D PCl6–
(Total 1 mark)
B
Which is the most likely bond angle around the oxygen atom in ethanol?
A 104.5°
B 109.5°
C 120°
D 180°
A
Which is the correct crystal structure for the substance named?
Iodine Simple molecular
Diamond ionic
Sodium chloride giant covalent
Graphite metallic
a
iodine simple molecular
Which species has one or more bond angle(s) of 90°?
A CH4
B NH4+
C ClF4−
D AlCl4−
C
Which compound has the highest boiling point?
CH3CH2CH2OH
CH3CH2CHO
CH3COCH3
CH3COOCH3
A
Which molecule does not have a permanent dipole?
CH3Cl
CHCl3
CF4
CHCl2F
CF4
Which of these species is not planar?
HCHO
CH3+
CH3OH
C2H4
CH3OH
Which of these statements best describes a dative covalent bond?
A A pair of electrons shared between two atoms where each atom has donated one electron.
B A pair of electrons shared between two atoms where one atom has donated two electrons.
C Two pairs of electrons shared between two atoms where each atom has donated one electron.
D Two pairs of electrons shared between two atoms where each atom has donated two electrons.
B
Which molecule is the least polar?
A Bromomethane
B Dibromomethane
C Tribromomethane
D Tetrabromomethane
D
Which statement about intermolecular forces is not correct?
A Intermolecular forces exist between all simple molecules.
B Hydrogen bonding occurs between HBr molecules.
C Hydrogen bonding is the strongest intermolecular force in liquid ethanol.
D Hydrogen bonds occur between C=O and H−N in proteins.
B
Which of these species has a trigonal planar structure?
A PH3
B BCl3
C H3O+
D CH3−
B
Use your understanding of intermolecular forces to predict which of these compounds has the highest boiling point.
A HF
B HCl
C HBr
D HI
A
HF
Which type of bond is formed between N and B when a molecule of NH3 reacts with a molecule of BF3?
A Ionic.
B Covalent.
C Co-ordinate.
D Van der Waals.
C
Which of these atoms has the highest electronegativity?
A Na
B Mg
C Cl
D Ar
C
What is the formula of calcium nitrate(V)?
A CaNO3
B Ca(NO3)2
C Ca2NO2
D Ca(NO2)2
B
Which of these substances does not show hydrogen bonding?
A HF
B NH3
C CH3COOH
D CHF3
D
Which of these substances has permanent dipole-dipole attractions between molecules?
A CCl4
B C2F4
C (CH3)2CO
D CO2
C
Which molecule is not able to form a co-ordinate bond with another species?
A BH3
B CH4
C NH3
D H2O
B
CH4
Which species has a square planar shape?
A NH4+
B SF4
C XeF4
D PCl4+
c
Which bond has the most unsymmetrical electron distribution?
A
H–O
B
H–S
C
H–N
D
H–P
a
Which statement about inorganic ionic compounds is always correct?
A
They dissolve in water to give neutral solutions.
B
They release energy when they melt.
C
They contain metal cations.
D
They form giant structures.
d
Which species has a lone pair of electrons on the central atom?
A
CO2
B
SO2
C
PCl6‒
D
SO42–
b
In which substance do covalent bonds break when it melts?
A
hexane
B
ice
C
iodine
D
silicon dioxide
d
In which molecule are all the atoms in the same plane?
A
CH3CHO
B
CH3NH2
C
C6H5Cl
D
C6H5CH3
c
Which molecule has a permanent dipole?
A
BF3
B
NH3
C
SiCl4
D
SO3
b
Which substance contains delocalised electrons?
A
cyclohexane
B
graphite
C
iodine
D
sodium chloride
b
Which polymer has hydrogen bonding between the polymer chains?
A
Kevlar
B
PVC
C
poly(phenylethene)
D
Terylene
a
Which compound contains a co-ordinate bond?
A
HF
B
NH3
C
CHCl3
D
NH4Cl
D
This question is about pentan-2-ol and pent-1-ene.
(a) The boiling point of pentan-2-ol is 119 °C. The boiling point of pent-1-ene is 30 °C. Explain why pentan-2-ol has a higher boiling point than pent-1-ene.
- pentan-2-ol has stronger intermolecular forces/ hydrogen bonds are stronger than van der Waals’ forces
- pent-1-ene has van der Waals’ forces (only)
- pentan-2-ol (also) has hydrogen bonds
Pent-1-ene is formed by the elimination of water from pentan-2-ol. State the reagent and condition for this reaction.
Outline the mechanism for this reaction.
Reagent
Condition
reagent = conc sulfuric acid or conc phosphoric acid
The melting point of XeF4 is higher than the melting point of PF3
Explain why the melting points of these two compounds are different.
In your answer you should give the shape of each molecule, explain why each molecule has that shape and how the shape influences the forces that affect the melting point. [6]
Stage 1 electron pairs
1a XeF4 4BP and 2LP around Xe
1b PF3 3BP and 1LP around P
Stage 2 explanation of shapes
- XeF4 is square planar/ PF3 is pyramidal
- Electron pairs repel as far as possible or Lone pair repels more than bonding pairs
Stage 3 IMF
- XeF4 has vdw forces and PF3 has dipole-dipole forces
- Stronger/more intermolecular forces in XeF4
- Due to larger Mr or more electrons or larger molecules or packs more closely together
Which has a bond angle of 109.5°?
A
C (diamond)
B
C (graphite)
C
NH2–
D
NH3
A
This question is about compounds that contain fluorine. (a) Sodium fluoride contains sodium ions (Na+) and fluoride ions (F–).
Na+ and F– have the same electron configuration.
Explain why a fluoride ion is
-Fluoride ion has (two) fewer protons/lower nuclear charge
- Weaker attraction between nucleus and (outer) electrons
Explain, in terms of structure and bonding, why the melting point of sodium fluoride is high.
(Electrostatic) forces of attraction between oppositely charged ions/Na+ and F–
Lots of energy needed to overcome/break forces
The ion H2F+ is formed when hydrogen fluoride gains a proton as shown in the equation HF + H+ → H2F+
Name the type of bond formed when HF reacts with H+
Explain how this bond is formed.
Type of bond
Explanation
Type of Bond: Coordinate bond / dative (covalent) bond
Explanation: A (lone) pair of electrons is donated from F
Methoxymethane (CH3OCH3) is an isomer of ethanol.
The table shows the boiling points of ethanol and methoxymethane.
Compound
Boiling point / °C
ethanol 78
methoxymethane −24
In terms of the intermolecular forces involved, explain the difference in boiling points.
Hydrogen bonds (between ethanol molecules)
(permanent) dipole-dipole OR van der Waals force (between methoxymethane molecules)
Hydrogen bonds are stronger/est intermolecular force
Which is not responsible for conduction of electricity?
A
The sodium ions in molten sodium chloride
B
The electrons between layers of carbon atoms in graphite
C
The bonding electrons in a metal
D
The lone pair electrons on water molecules
D
The lone pair electrons on water molecules
There are two lone pairs of electrons on the oxygen atom in a molecule of oxygen difluoride (OF2).
Explain how the lone pairs of electrons on the oxygen atom influence the bond angle in oxygen difluoride.
Lone pairs repel more than bond pairs
bond angle will be lower (than regular tetrahedral angle) / bond angle of 103-106°
Silicon tetrafluoride (SiF4) is a tetrahedral molecule.
Deduce the type of intermolecular forces in SiF4
Explain how this type of intermolecular force arises and why no other type of intermolecular force exists in a sample of SiF4
Intermolecular forces in SiF4
Explanation
Van der Waals forces
(Uneven distribution of electrons in) one molecule induces dipole in neighbouring molecule
symmetrical molecule / dipoles cancel
OR
no hydrogens bonded to F (N or O), therefore no hydrogen bonding
This question is about intermolecular forces.
(a) Give the meaning of the term electronegativity.
Power of an atom to attract a pair of electrons in a covalent bond.
Explain how permanent dipole-dipole forces arise between hydrogen chloride molecules
Difference in electronegativity leads to bond polarity
(dipoles don’t cancel therefore the molecule has an overall permanent dipole) and there is an attraction between ∂+ on one molecule and ∂− on another
