Inorganic Chemistry-Periodic Properties(Group 14 Elements)

 

Group 14 Elements

            Group 14 contains five elements, namely Carbon, Silicon, Germanium, Tin and Lead. Carbon is an essential constituent of all organic matter Silicon is an important constituent of inorganic matter.

            Carbon and Silicon are typically non-metals Germanium has intermediate character while Tin and Lead are distinctly metals.

 

Electronic Configuration:-

            The electronic configuration of elements of group 14 elements.

Elements	Atomic Number	Electronic Configuration
C- Carbon	6	[He] 2S22P2
Si- Silicon	14	[He] 3S23P2
Ge- Germanium	32	[Ar] 3d104S24P2
Sn-Tin	50	[Kr] 4d105S25P2
Pb- Lead	82	[Xe] 4f145d106S26P2

 

            The general outer electronic configuration of the elements of 14 group is ns²np².

General Characteristics of Group 14 Elements:-

1.      Atomic Radius:- The atomic radius increases from top to bottom with increases atomic number.

2.      Melting and Boiling Point:-  The melting and boiling point of Carbon is high. The values decreases as we move from Carbon to Lead. The melting points of Tin and Lead are relatively low.

3.      Ionization Potential:-

C	Si	Ge	Sn	Pb
1086	786	761	708	716

 

-          Ionization energy of Carbon is quite high, because small size of the Carbon atom.

-          There is sharp decrease in the I. P. from C to Si. This is due to an increase the size of Si atom.

-          There is very small decrease in I. P. from Si to Sn. This is because of the d electrons which are now present in the inner configuration of Ge &Sn, shield the nuclear charge less effectively than S & P electrons.

-          In the last element, Pb there is f electrons in the inner configuration which shield the nuclear charge less effectively even than the d electrons. Due to this, slightly increase I. P. from Sn to Pb.

 

 

4.      Oxidation States:-

Elements	Oxidation State
C	+4
Si	+4
Ge	+2 +4
Sn	+2 +4
Pb	+2 +4

 

All the elements have the oxidation state of +4. The +4 state is much greater important in C & Si and +2 state become increasingly important for Germanium, Tin & Lead.

5.      Metallic and Non- Metallic Character:-

The change from non – metallic to metallic character with increase in atomic number in the same group. The first two elements C & Si are distinctly non – metals even though electrical properties of Silicon are like those of a semi – metal. The third element, Germanium is a semi – metal while the last two elements, Tin & Lead are distinctly metals.

6.      Electronegativity :-

Carbon is most electronegative element of this group. The electronegativity decreases on moving down the group but not after Silicon.

C	Si	Ge	Sn	Pb
2.5	1.9	2.0	1.8	1.8

 

            Electronegativity order of group 14 elements is:

            C ˃ Ge ˃ Si ˃ Sn῀₌ Pb

7.      Tendency to form Chains(Catenation):-

The shows the remarkable property of catenation i.e. to form chains of identical atoms.

            Silicon has much smaller tendency to form chains.

            Germanium has still smaller tendency while Sn and Pb have hardly any tendency to do so.

            Thus in group 14, tendency to catenation decreases in the order.

                        C ˃ Si ˃ Ge ˃ Sn ˃ Pb

            Catenation properties depends upon C-C, Si-Si, Ge-Ge, Sn-Sn & Pb-Pb.

8.      Allotropy:-

Most of the elements of group 14 shows allotropy.

            Carbon exists in two forms: 1) crystalline form i.e. diamond and graphite., 2) Amorphous form

i.e. coal, coke, charcoal, carbon black etc.

Silicon is known to exist in crystalline and amorphous forms.

Germanium also exists in two crystalline forms.

Tin exists in three solid form i.e. grey Tin, white Tin & Rhombic Tin.

Grey Tin:- It is stable below 18⁰C, It is poor conductor of electricity & exist in powder form.

White Tin:- It is soft, ductile and good conductor of electricity. It is stable above 18⁰C.

Rhombic Tin:- Rhombic Tin is stable above 161⁰C.

Hydrolysis of Group 14 Elements or IV A elements

All the elements of this group form covalent hydrides. Covalent character and Stability of hydrides decreases as we move from C to Pb.

1.      Hydrides of Carbon:-

Carbon forms a number of hydrides, known as alkanes(general formula: C_nH_2n+2), alkene

 (C_nH_2n), alkynes(C_nH_2n-2) and a number of aromatic compounds i.e. benzene, toluene, xylene)

2.      Hydrides of Silicon:-

These compounds are similar to hydrides of carbon but they are much less stable.

Hydrides of Silicon are called Silanes and have general formula Si_nH_2n+2. Silane with n up to 8 is known.

Ex.:- Silane(SiH₄), disilane(Si₂H₆), trisilane(Si₃H₈), tetrasilane(Si₄H₁₀),… etc

The first two members are colourless gases while third and subsequent members are liquid.

SiH₄ is stable at room temperature. Thermal stability decreases with increasing chain length.

3.      Hydrolysis of Germanium:-

The hydrides of germanium called germanes have the general formula Ge_nH_2n+2(n up

to 5). Three hydrides of germanium are more commonly known. These are monogermane GeH₄,

digermane Ge₂H­₆&trigermane Ge₃H₈.

The first two compounds are colourless gases while the higher germanes are liquids

The Boiling Point of hydrides of Germanium increases with increase chain length.

	GeH4	Ge2H6	Ge3H8	Ge4H10	Ge5H12
B.P.(0C)	-88	22	110.5	177	234

Germanes are less volatile and less reactive than the corresponding Silanes.

4.      Hydrides of Tin and Lead:-

Two hydrides of Tin, monostannane (S_nH₄) and distannane (S_n2H₆) are known.

            The freezing and boiling points of S_nH₄ are -146⁰C and -52⁰C respectively. It is not stable and

decomposes slowly even at room temperature into Tin and Hydrogen. Distannane Sn₂H₆ is much

less stable. Higher hydrides of Tin are not known Pb does not form hydrides.

 

Oxides of Group 14 Elements

The elements of this group form two types of oxides namely Monoxide(Mo) and Dioxides(Mo₂).

1.      Monoxides:-

CO, SiO, GeO, SnO, &PbO

I)                   CO:-

Carbon monoxide is obtained by burning carbon in a limited supply of Oxygen.

It is colorless, odorless toxic gas. Its toxic nature is due to its ability to form a complex with hemoglobin in the blood.

CO is an essential constituent of gaseous fuels like water gas, producer gas.

II)                SiO-

Sio can be obtained by heating SiO₂ with Si at about 1300⁰C in vaccum.

SiO₂ + Si →2SiO

It is neutral in nature.

III)             GeO:-

Geo can be obtained by dehydrating Ge(OH)₂ or by heating Ge and GeO₂ at about 1000⁰C.

Ge(OH)₂ → GeO + H₂O                   It is basic in nature

GeO₂ + → 2GeO

IV)             PbO:-

PbO is obtained by reacting Molten Lead with air or Oxygen above 600⁰C.

It is amphoteric.

 

2.      Dioxides:-

Co₂, SiO₂, GeO₂, SnO₂& PbO₂.

            Lead also forms an oxide, PbO₃ which is a mixed oxide of PbO and PbO₂.

            Among the Monoxides CO &SiO are neutral, GeO is basic while SnO&PbO are amphoteric.

            Among the Dioxides CO₂ is acidic and SiO_2­ is weakly acidic. While GeO₂, SnO₂& PbO₂ are amphoteric.

 

I)                   CO₂:-

CO₂is obtained on burning Carbon in excess of Air. It is Colorless gas with a taint pungent odor and slight acidic taste solid CO₂ known as dry ice.

The structure of CO₂ is linear O=C=O.

II)                SiO₂:-

It is called as Silica, it is obtained by heating Silicon in oxygen.

Si + O₂→ SiO₂

Sio₂ is hard solid with very high M.P.

Structure of SiO₂ is:

III)             GeO₂& SnO₂:-

They are obtained by heating Ge & Sn with oxygen or air.

Ge + O₂→ GeO₂                      Sn + O₂→ SnO₂

GeO₂& SnO₂ are amphoteric.

IV)             Lead Pxide:-

PbO₂ is formed by electrolytic oxidation of lead.

It is amphoteric.