Bonding questions Flashcards
PMT exam questions
Compare the bonding between Na and Mg
Mg has a stronger metallic bonding than Na and hence a higher boiling point
Metallic bonding is stronger in Mg than Na as there are more electrons released into the sea of electrons. Mg ion is also smaller and has one more proton. Stronger electrostatic attraction between the positive metal ions and the delocalised electrons high energy is needed to break bonds
Explain why the bp of pentan -2-ol is higher than the bp of pent-1-ene
Pentan-2-ol has stronger inter molecular forces
pent1ene has van deer waals only
pentan1ol has hydrogen bonds too which are stronger than van deer waals
Explain why mp of xef4 is different to the mp of pf3
Stage 1 electron pairs
1a XeF4 4BP and 2LP around Xe
1b PF3 3BP and 1LP around P
Stage 2 explanation of shapes
2a XeF4 is square planar
2b PF3 is pyramidal (allow tetrahedral)
2c Electron pairs repel as far as possible or Lone pair repels more than bonding
pairs
Stage 3 IMF
The relative strength of the intermolecular forces in the molecules must be
explained to gain maximum marks.
3a XeF4 has vdw forces and PF3 has dipole-dipole forces (and vdw)
3b Stronger/more intermolecular forces in XeF4
3c Due to larger Mr or more electrons or larger molecules or packs more closely
together
Explain why a flouride ion is larger than a sodium ion
- Flourine has two fewer protons
- Weaker electrostatic attraction of outer electrons to the nucleus
Name the type of bond formed when a proton is added to hydrogen flouride
- co ordinate bond
- flourine donates a lone pair of electrons to the H
Which molecule is unable to form a co-ordinate bond with another species? 1 mark
- BH3
- CH4
-H2O
-NH3
CH4, as it has no lone pairs to donate to an electron deficient species
Which species has a square planar shape? 1 mark
-XeF4
-SF4
-NH4+
-PCl4+
- XeF4 4bp and 2 lone pairs
Which bond has the most unsymmterical bond distribution? 1 mark
- H-O
- H-N
- H-P
-H-S
H-O as O is the most electronegative element, electron density in a covalent bond is more strongly attracted to the O causing more of a S- charge near the O
Which statement about inorganic ions is always correct? 1 mark
- Dissolve in water to form neutral solutions
- Form giant structures
-Release energy when melt
- Contain metal cations
- Form giant structures
Which species has a lone pair of electrons on the central atom?
- SO2
- CO2
-PCl6-
-SO42-
- SO2
In which substance do covalent bonds break when it melts? 1 mark
- Iodine
- Silicon dioxide
- Ice
-Hexane
ANS: Silicon dioxide
Covalent bonds must break in order for this to change state, a giant covalent structure
When ice melts, covalent bonds dont break, only hydrogen bonds
When iodine melts, covalent bonds dont break only van deer waals
When hexane melts intermolecular forces break, not covalent bonds
In which molecule are all the atoms in the same plane?
C6H5Cl
C6H5CH3
CH3NH2
CH3CHO
- C6H5Cl
Which molecule has a permanent dipole?
- NH3
- SO3
-BF3
-SiCl4
- NH3 bond polarities do not cancel out due to the asymetrical nature of the molecule leaving it with a permanent dipole moment
Which compound contain a co- ordinate bond?
- HF
- NH4Cl
-CHCl3
-NH3
- NH4Cl- Cl donates a lone pair to the H in order to form a daitive bond
Which has a bond angle of 109.5?
C diamond
C graphite
NH3
NH2-
Diamond, tetrahedral
Na and F have the same electron configuration, why is flourine a larger molecule than sodium? 2 marks
Flourine has 2 fewer protons than sodium
Weaker electrostatic attraction between nucleus and outer electrons
Explain in terms of structure and bonding why the melting point of sodium flouride is high 2 marks
- Oppositley charged ions, Na+ and F- experience an electrostatic force of attraction
- Requires a high amount of energy to overcome these forces/ ionic bonding
Name the type of bond formed when HF reacts with H+
2 marks
- Co - ordinate bond
- Flourine donates a lone pair of electrons in order to form a co ordinate bond with H which has no electrons
What type of change occurs when water is vapourised?
- An exothermic change occurs
- Intermolecular forces are overcome
-Covalent bonds are broken
-Total energy of the molecules decreases
- Intermolecular forces are overcome ( hydrogen bonds)
Which compound has the highest boiling point
CH3CH2CH2Br
-CH3CH2CH2F
-CH3CH2CHO
-CH3CH2COOH
-CH3CH2COOH
