Group 14

Physical properties of Group 14 elements	2	Candidates should be able to: (a) explain the trends in physical properties (melting points and electrical conductivity) of Group 14 elements: C, Si, Ge, Sn, Pb.
11.2 Tetrachlorides and oxides of Group 14 elements	4	Candidates should be able to: (a) explain the bonding and molecular shapes of the tetrachlorides of group 14 elements;  (b) explain the volatility, thermal stability and hydrolysis of tetrachlorides in terms of structure and bonding; (c) explain the bonding, acid-base nature and the thermal stability of the oxides of oxidation states +2 and +4.
11.3 Relative stability of +2 and +4 oxidation states of Group 14 elements	2	Candidates should be able to: (a) explain the relative stability of +2 and +4 oxidation states of the elements in their oxides, chlorides and aqueous cations.
11.4 Silicon, silicone and silicates	1	Candidates should be able to: (a) describe the structures of silicone and silicates (pyroxenes and amphiboles), sheets (mica) and framework structure (quartz) (general formulae are not required); (b) explain the uses of silicon as a semiconductor and silicone as a fluid, elastomer and resin; (c) describe the uses of silicates as basic materials for cement, glass, ceramics and zeolites.
11.5 Tin alloys	1	Candidates should be able to: (a) describe the uses of tin in solder and pewter.

1. The members of group 14 in the periodical table are Carbon, Silicon, Germanium, Tin and Lead

2. Group 14 is the only group which contain all 3 major classification of elements: metal, metalloid(semi-metal)  and non-metal

3. The expected similarity in appearance between elements in the same Group is much less apparent in Group 14, where there is  a considerable change in character on going down the Group.

4. Carbon is a dull black colour in the form of graphite, or hard and transparent in the form of diamond; silicon and germanium are dull grey or black; tin and lead are a shiny grey colour.

5. The variation of Group 14 is based on the characteristic of each elements. (ns² np²)

Element	Carbon	Silicon	Germanium	Tin	Lead
Classification	Non–metal	Metalloid		Metal
Valence electron	2s22p2	3s23p2	4s24p2	5s25p2	6s26p2
Atomic radius(nm)	0.077	0.117	0.122	0.148	0.154
Melting point(°C)	3700	1410	936	232	328
Boiling point(°C)	4620	2680	2820	2270	1730
First ionization energy(kJmol⁻1)	1085	788	760	705	714

a) Atomic Radius

1. Atomic radius increase when goes down to Group 14. When the number of electrons increases, the number of shell required to fill in the electrons increase. This will increase the screening effect of the atom causing the effective nuclear charge decrease.

2. As the attraction forces between the outermost electron and the nucleus decrease, atomic radius become larger.

 

Element	Atomic Radius/nm
C	0.077
Si	0.117
Ge	0.122
Sn	0.148
Pb	0.154

b) Melting point

1. As the properties of Group 14 elements are different, it has different molecular structure.

2. Carbon, silicon and germanium have gigantic molecular structure.

3. The melting point decrease when goes down to from carbon to germanium.

Element	Giant molecular structure Melting Point/K
C	3830
Si	1683
Ge	1210.6
Sn	505.1
Pb	600.7

4. This is due to bonding length of C – C ; Si – Si ; and Ge – Ge  become longer, so the covalent bond become weaker as the length increase.

                         

5.  As for tin (Stanum) and lead (Plumbum), they have strong metallic bond.

6. Lead has higher melting point than tin, as the arrangement of the metallic atom of lead are more closely packed (faced centered cubic) than tin (tetragonal structure/more open) in solid lattice.

7. The close packing of lead increase the strength of the metallic bond even though the atomic radius of lead is larger than tin.

Exam Question

1. Which of the following is responsible for the increasing relative stability of the +4 oxidation state with the increasing proton number of the Group 14 elements?                                   

                                                                                                                 [STPM 1999]

A    The elimination of the two electrons in the s orbital becomes increasingly more  

       difficult.

B    The elimination of the two electrons in the p orbital becomes increasingly more 

       difficult.

C    The elimination of the four valence electrons becomes increasingly more difficult.

D    The inert pair effect increases.

E    The ionization energy of the elements increases

2. A tetrachloride of Group 14, XCl₄, has the following properties. [STPM 1999]

(i) It is easily hydrolysed

(ii) Unstable to heat

(iii) Decomposes at room temperature according to the equation XCl₄→XCl₂ + Cl₂ , X could be ………………..

A    germanium      B    carbon        C    lead          D    solicon            E    tin

3. Which of the following best explains the decreasing thermal stability of the chlorides and oxides in the oxidation state of +4 of the Group 14 elements (carbon to lead) in the Periodic Table when descending the group?                 [STPM 2000]

A The bond energy increases.

B The first and second ionization energy decreases.

C The standard electrode potential decreases.

D The presence of the inert pair effect of the s orbital electrons.

E The ease of elimination of four electrons increases.

4. Which of the following statements is true regarding the conductivity of graphite?       

                                                                                                                               [STPM 2000]

A   Its conductivity is higher than those of the metals.

B    Its conductivity is due to its three dimensional structure.

C    Its conductivity is due to the presence of delocalised electrons.

D    Its conductivity is due to the formation of sp² hybrid orbitals.

E    Its conductivity is due to its electronic coniguration of 1s² 2s² 2p².