Bonding Flashcards
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)
1
(permanent) dipole-dipole OR van der Waals force (between
methoxymethane molecules)
Allow vdW
Hydrogen bonds are stronger/est intermolecular force
22.
This question is about compounds containing fluorine.
(a) Draw the shape of a molecule of krypton difluoride (KrF2).
Include in your answer any lone pairs of electrons that influence the shape.
Name the shape produced by the atoms in a KrF2 molecule and suggest a
bond angle.
Linear
1
180°
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
If just covalent, then do not award M1 but mark on
1
Explanation: A (lone) pair of electrons is donated from F
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.
b PF3 3BP and 1LP around P
Stage 2 explanation of shapes
2a XeF4 is square planar
Or
2b PF3 is pyramidal (allow tetrahedral)
Or
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 lar
CH3Cl bond angle and shape
distorted tetrahedral
