Physical and chemical properties of group 4A elements - Group IVA in Periodic Table

 

Group IVA Elements

Group 4 Elements Electronic Configuration

Elements of the fourth Group are:

 

Element	symbol	electron configuration
Carbon	C	[He]2s2 2p2
Silicon	Si	[Ne]3s22p2
Germanium	Ga	[Ar]4s2 2p2
Tin	Sn	[Kr]5s2 2p2
Lead	Pb	[Xe]6s2 2p2

 

Carbon is indisputably a nonmetal, and silicon has properties of semimetals. Germanium is considered semimetal.

Oxidation State of Group 4 Elements (Valency of Group 4 Elements)

 

The elements of group IVA have in common the oxidation states of +2 and +4, while +4 state is very important for carbon and silicon, the +2 state becomes increasingly important for germanium, tin and lead due to inert pair effect.

 

Abundance and Extraction of Group IVA Elements:

Carbon occurs naturally in the allotropic forms diamond and graphite and much more abundantly in coal.

 

Silicon is the second most abundant element after oxygen and is found in silicate minerals.

 

Silicon and germanium used in electronic industry, and can be obtained in pure form by the following process:

 

A.   Reduction of silicon dioxide, with carbon.             

 

B.    Then silicon is converted to the tetrachloride by direct reaction with chlorine: 

                            

              

Silicon tetrachloride is volatile and can easily by purified by distillation, then the purified silicon is recovered by reducing chlorine with hydrogen.

                                     

                  

The common ore of lead is galena, PbS. To recover lead, the sulfide is converted to PbO, which is then reduced with carbon.

Tin occurs as the oxide SnO₂, which can be reduced directly with carbon.

Physical and chemical properties of group 4A elements

 

Carbon:

Carbon exist in two allotropic forms diamond and graphite. Of the two allotropic forms of carbon, graphite is slightly more stable at 25^oC and l atm.

 

Diamond	Graphite
It is purest kind of C. It has a tetrahedral structure i.e. each carbon atom covalently bonded to 4 carbon atoms, thus display Sp3 hybridization. Diamond is transparent insulator	Graphite less pure than diamond It has sp2 structure and the carbon atoms form layers. These planes are held by van der Waal forces       Graphite is dark, opaque, and has electrical conductivity, because each C atom is surrounded by 3C atoms therefore several free electrons are present.

 

Most of carbon compounds contain a number of carbon-carbon bonds. Most

organic compounds apparently owe their stability to the strong bonds that carbon forms with itself. In addition to a single C-C bond, there are double C=C bonds and triple C=C bonds.

 

Carbon Oxides:

Carbon forms three oxides that are well characterized: carbon monoxide, carbon dioxide, and carbon suboxidc, C₃O₂.

Carbon monoxide is isoelectronic with nitrogen, the simple electron-dot structure that satisfies the octet rule also indicates that carbon monoxide is triply bonded (2 π bonds + 1  bond). and is then sp hybridized.

                                                      :C:::O:

The nonbonded electrons on the carbon atom in carbon monoxide can be donated to electron acceptor (electron deficient molecules) as B₂H₆, to form borine carbonyl, BH₃CO

Silicon:

 

Elemental silicon has a silvery metallic luster, but its electrical conductivity is lower than the metals. Its crystal lattice is same as diamond.

 

While silicon is rather inert at room temperature, it reacts at higher temperatures with all the halogens to form tetrahalides, with oxygen to form SiO₂, and with nitrogen to formSi₃N₄.

Silicon Oxide (Silica):

Silicon dioxide or silica exists as a three-dimensional network solid of high stability. In one crystal form of SiO₂, the silicon atoms are arranged exactly like the carbon atoms in diamond, except that oxygen atoms are midway between them.

 

Because of the great strength of the Si-O bond, fused quartz is thermally stable and chemically inert to all substances except HF, F₂, and hot alkali. In addition it is an excellent electrical insulator even at high temperatures.

Silicon hydrides:

Several silicon hydrides, or silanes, are known. All have the general formula Si_nH_2n+2, and thus are similar to the saturated hydrocarbons and called silanes.

 

In the hydrocarbon series, the number of carbon atoms in a chain can apparently have any value, but among the silanes, the most complicated known compound is Si₆H₁₄. this because the weak Si-Si.

 

In silicon hydrides there is no double bonds (or multiple bonds) like carbon

 

The silanes are colorless, relatively volatile substances. They are all very reactive

                   

            

 

They also react with HCl to give chlorosilanes.

                            

It is possible to synthesize such molecules as (CH₃)₃SiCl, (CH₃)₂SiCl₂  and CH₃SiCl₃. These substituted chlorosilanes on hydrolysis they yield polymeric molecules of high molecular weight called silicones.

Physical properties of silicones

All the silicones tend to be:

                                                     1.            Water repellent,

                                                     2.            Heat resistant,

                                                     3.            Electrically insulating

                                                     4.            Chemically inert.

These properties make them useful as lubricants, insulators, and protective coatings.