1.3 Assessed Homework Mark Scheme 2008

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1. 3 Assessed Homework Mark Scheme 2008

1. (a) (i) Covalent (1)

(ii) Co-ordinate (1) (or dative)

(iii) Both / two / pair electrons come from nitrogen (1)

(iv) 4 bonding / electron pairs (1)

repel equally (1)

OR are identical

as far apart as possible (1)

OR to position of minimum repulsion

tetrahedron (1) 7

(b) Power (or ability) of an element / atom to attract electron pair / electrons/
an electron/electron density (1)

in a covalent bond (1)

Allow attract from, withdraw in, do not allow remove from, withdraw from.

Or small, slight, partial positive charge

(ii) H < N (1) 2

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2. (a) (i) Electronegativity (difference) or suitable description (1)

Accept F and Cl are highly electronegative
Not both atoms are highly electronegative

(ii) HF = hydrogen bonding (1)
HCl = (permanent) dipole-dipole bonding or even van de Waals’ (1)
Hydrogen bonding stronger / is the strongest IMF (1) 4

Accept a statement that HF must have the stronger IMF, even if no IMFs identified

The explanation must be based on intermolecular forces/attractions

Note: if the explanation is clearlyintramolecular = CE

(b) Electron pair or lone pair donated (1)

Do not accept ‘donation of electrons’

From chloride ion to Al or AlCl3 (1) 2

M1 can be earned by a general explanation of coordinate bonding, even if the electron pair is said to come from Al. The second mark, M2, is for this specific bond

Ignore missing charge

PCl5 shown as trigonal bipyramid PCl4+ shown as tetrahedral
[Look for: ONE solid linear Cl-P-Cl bond] NO solid linear Cl-P-Cl bonds]

Bond Angle(s) 90° and 120° (1) Bond angle(s) 109 or 109. 5° (1)

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3. (a) 4 LiH + AlCl3 à LiAlH4 + 3 LiCl 1

(b) H – = 1s2 or 1s2 1

(Not distorted tetrahedral)

(Equal) repulsion 1
between four bonding pairs / bonds 1

(Not repulsion between H atoms loses M2 and M3)

(Not ‘separate as far as possible’)

(‘4’ may be inferred from a correct diagram)

(d) Dative (covalent) or coordinate                                                                  1
Lone pair or non-bonding pair of electron or both e–                                 1
QoL Donated from H– to Al or shared between H and Al                  1

(tied to M2)

(Not ‘from H atom’) (Not ‘to Al ion’) (Not ‘e–s transferred’)

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