Q20.
(a) (i) shared pair of electrons
Can have one electron from each atom contributes to the bond
Not both electrons from one atom
1
(ii)
1
Only
Ignore state symbols even if wrong
(b)
OR
Allow any structure with 4 bp
In CClF2, watch for Cl in centre- it must be C
Ignore wrong bond angles
Representations of lone pairs allowed are the two examples shown with or without the electrons in the lobe.
Also they can show the lone pair for either structure by two crosses/dots or a line with two crosses/dots on it e.g.
Or a structure with 3 bp and 2 lp
1
(c) Dipole – dipole
Allow van der Waals/vdw/London/dispersion/temporary dipole – induced dipole
Not dipole alone
1
(d) (i) Coordinate/dative (covalent)
If wrong CE = 0/3 but if ‘covalent’ or left top line blank, mark on.
1
(Lone) pair of electrons/both electrons (on F–)
CE if lone pair is from B
1
Donated from F–/fluoride or donated to the BF3
Must have the – sign on the F ie F–
Ignore Fl–
M3 dependent on M2
1
(ii) 109° to 109.5°
1
(e)
For 1 mark allow 238 as numerator and 438 as denominator or correct strings
1
= 54.3%
2 marks if correct answer to 3 sig figs.
54% or greater than 3 sig figs = 1 mark
1
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