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Exercise 10 F6 Chemistry

2007-PI-essay

A.

3

/( )

( )

B.

6

( )

+

C.

5

:

:

(i) ;

(ii) d-

:

/

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/

Fe ( ) Fe ( ) /

(hcc,bcp,fcc)

( ,)

( 6 ) ( )

10-8 67 5

6 45-4 3

3-2 21-0 1

(i)

(ii)

(iii)

(iv)

(iv)

( 4 )( )

10-7 4

6-5 34-3 2

2 1

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9. Chemical Knowledge (10 marks)

Chemical Knowledge covers three areas A, B and C.

A. Bonding in metals

max. 3

- Metals consist of a regular three-dimensional array of cations and delocalised mobile electrons.(Accept diagrams to show the 'sea of electron' model of metal.)

- The attraction between the cations and the de localised electrons gives rise to metallic bond

- Metallic bond is non-directional- The strength of metallic bond depends on the size of atom and the number of electrons per atom

involved in metallic bond

(Additional bonus will be awarded to description of the band theory.)

B. Structure of metals

max.6- Metals exist mainly in closed packed structure (hcp and ccp structures) and open structure.

- Description of the hcp structure and ccp structure + appropriate diagrams.

- Packing efficiency

- Tetrahedral holes and octahedral holes- Coordination number of atoms in closed packed and open structures- unit cells

- Description of dislocations and defects in metals

C. How bonding and structures affect the physical properties of metals max. 5

- Electrical conductivity: Valence electrons in a metal will flow under the influence of an electric field.This gives rise to electrical conductivity.

- Mallability and ductility: Because of the non-directional character of metallic bond, layers of atoms inmetal can slide over one another. Metals can be deformed under stress.

- Melting point:

(i) For metals in the main groups, the melting point decreases as the group is descended, and increasesacross a period,

(ii) In general, the melting point of d-block elements is higher than that of the main group elements.

- Alloy formation : Filing of interstitial holes by atoms of a foreign metal/replacement of atoms by thoseof another metal. The properties of metals can be improved (changed) by alloy formation.

- Allotropes / phase transition as exemplified by Fe(bcc) and Fe(fcc), grey tin and white tin etc.- Density: Density of metals depends on relative atomic mass and degree of compactness of atoms in the

metal.- Metallic lustre with elaboration

Organisation (6 marks) (marks awarded)

mark for

C.K.

max.for

Orgn.General Guidelines for marking Organisation

10-8 6

7 5

6 4

5-4 3

(i) The essay should be clearly ORGANISED, with suitable DIVISIONS, PARAGRAPHS

AND SUB- HEADINGS. These should be clear to the reader.(ii) Terms must be clearly defined.

(iii) The essay should be LOGICALLY organised.

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3-2 2

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(4 marks)( marks awarded)This mark is awarded for the ability to PRESENT the organised Chemical Knowledge in a suitable, meaningfuland readable form.

NOTE: Marks awarded should be related to Chemical Knowledge.

mark for C.K. max.for Presentation.

10-7 4

6-5 3

4-3 2

2 1

The following are looked for:EQUATIONS, DIAGRAMS AND EXAMPLES

ENGLISH This mark is for the ability to express clearly in

English