CHEM 1 Bonding

Bonding1. (a) Name the type of force that holds the particles together in an ionic crystal.

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(b) What is a covalent bond?

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(c) State how a co-ordinate bond is formed.

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(d) Describe the bonding in a metal.

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(e) A molecule of hydrogen chloride has a dipole and molecules of hydrogen chloride attract each other by permanent dipole-dipole forces. Molecules ot chlorine are non-polar.

(i) What is a permanent dipole?

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(ii) Explain why a molecule of hydrogen chloride is polar.

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(iii) Name the type of force which exists between molecules of chlorine.

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(f) Show, by means of a diagram, how two molecules of hydrogen fluoride are attracted to each other by hydrogen bonding; include all lone-pair electrons and partial charges in your diagram.

CHEM 1 Bonding

(3)

(g) Why is there no hydrogen bonding between molecules of hydrogen bromide?

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(Total 15 marks)

2. The table below provides some information regarding the metals sodium, magnesium and iron.

M e l t i n g p o i n t / K

M e t a l l i c r a d i u s / n m

C r y s t a l s t r u c t u r e

s o d i u m

3 7 1

0 . 1 8 6

b o d y - c e n t r e d

m a g n e s i u m

9 2 3

0 . 1 6 0

c l o s e - p a c k e d

i r o n

1 8 0 8

0 . 1 2 6

b o d y - c e n t r e d

(a) Complete the electronic configurations for the metals sodium and iron. In each case state the block in the Periodic Table to which the element belongs.

Electronic configuration of sodium 1 s2 ..................................................................

Block to which sodium belongs ..................................................................................

Electronic configuration of iron 1 s2 .......................................................................

Block to which iron belongs .......................................................................................(4)

(b) Describe the bonding found in metals.

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(c) Use data from table above and your knowledge of the bonding in these metals to explain why the melting point of magnesium is higher than that of sodium.

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CHEM 1 Bonding

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(d) State and explain the similarities and differences in electrical conductivity of sodium, graphite and diamond.

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(Total 14 marks)

3. The diagram below represents a section of a crystal of silicon dioxide.

S i

O

OO

O O

S i

S i

S i

O

(a) Name an element which has a structure similar to this.

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(b) Name the type of bonding between silicon and oxygen in this crystal.

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(c) Name the type of structure illustrated by this diagram.

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(d) Describe the motion of the atoms in this crystalline solid.

CHEM 1 Bonding

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(e) In terms of structure and bonding, describe what happens to the atoms in this crystal when it melts.

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(f) Explain why this crystal is a non-conductor of electricity in the solid state and why graphite is a good conductor.

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(Total 9 marks)

4. (a) Co-ordinate bonding can be described as dative covalency. In this context, what is the meaning of each of the terms covalency and dative?

Covalency....................................................................................................................

Dative .........................................................................................................................(2)

(b) Write an equation for a reaction in which a co-ordinate bond is formed.

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(c) Why is sodium chloride ionic rather than covalent?

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(d) Why is aluminium chloride covalent rather than ionic?

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CHEM 1 Bonding

(e) Why is molten sodium chloride a good conductor of electricity?

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(f) Explain, in terms of covalent bonding, why the element iodine exists as simple molecules whereas the element carbon does not.

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(Total 12 marks)

5. The boiling temperatures, Tb, of some Group IV and Group V hydrides are given below

Compound CH4

SiH4

NH3

PH3

Tb/K 112 161 240 185

(a) The polarity of a carbon-hydrogen bond can be shown as –δ

C —+δ

H

(i) What does the symbol δ+, above the hydrogen atom, signify?

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(ii) Explain briefly, in terms of its shape, why a CH4

molecule has no overall polarity.

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(b) Name the type of intermolecular forces which exist between CH4

molecules in liquid

methane.

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(c) Explain why the boiling temperature of PH3

is greater than that of CH4.

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CHEM 1 Bonding

(d) Explain why the boiling temperature of NH3

is greater than that of PH3

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(e) Sketch a diagram to show the shape of a molecule of NH3

and indicate on your

diagram how this molecule is attracted to another NH3

molecule in liquid ammonia.

(3)

(f) Suggest why the strength of the C–H bond in CH4

is greater than that of the Si–H bond in

SiH4. State the relationship, if any, between the strength of the covalent bond in CH

4 and

the boiling temperature of CH4

Reason for stronger C-H bond....................................................................................

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Relationship between covalent bond strength and boiling temperature.....................

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(Total 14 marks)

6. (a) (i) State one feature which molecules must have in order for hydrogen bonding to occur between them.

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(ii) Give the name of the type of intermolecular bonding present in hydrogen sulphide, H

2S, and explain why hydrogen bonding does not occur.

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CHEM 1 Bonding

(iii) Account for the much lower boiling point of hydrogen sulphide (–61 °C) compared with that of water(100 °C).

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(b) Protein molecules are composed of sequences of amino acid molecules that have joined together, with the elimination of water, to form long chains. Part of a protein chain is represented by the graphical formula given below.

C N N NC C CC C C

R R R ROOO

H H H H HHH

Explain the formation of hydrogen bonding between protein molecules.

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(Total 9 marks)

7. (a) The diagram below represents a part of the structure of sodium chloride. The ionic charge is shown on the centre of only one of the ions.

+

(i) On the diagram, mark the charges on the four negative ions.

(ii) What change occurs to the motion of the ions in sodium chloride when it is heated from room temperature to a temperature below its melting point?

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(b) Sodium chloride can be formed by reacting sodium with chlorine.

CHEM 1 Bonding

(i) Write an equation for this reaction.

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(ii) A chloride ion has one more electron than a chlorine atom. In the formation of sodium chloride, from where does this electron come?

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(c) In some ionic compounds the chloride ions are polarised.

(i) What is a polarised chloride ion?

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(ii) What feature of a cation causes a chloride ion to become polarised?

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(d) (i) What is a covalent bond?

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(ii) What property of the atoms joined by a covalent bond causes the bond to be polar?

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(Total 9 marks)