Trends in chemical reactivity of Group 14 elements

Chemical properties of Group 14 elements

1. The elements of group 14 form covalent hydrides of the type MH4. The number of hydrides, their thermal stability and their ease of formation decreases as we move down the group. The reducing power of hydrides increases as we move from CH4 to PbH4. Carbon forms a large number of cyclic and acyclic hydrides known as hydro carbons. Si andGe form hydrides of the formula MnH2n+2 (where M=si, n=1 to 8; M=Ge, n=1 to 5). The hybrides of silicon are called silanes while those of Germanium are called Germanes. Tin and Lead from one hydride each, ie SnH4 (Stannane) and PbH4 (Plumbane).

2. Elements of Group 14 form two types of halides, tetrahalides (MX4) and dihalides (MX2)
The tetrahalides are covalent and have tetrahedral geometry. Their thermal stability decreases down the group. The tetrahalides of group 14 except that of carbon are readily hydrolysed.

SiCl4 + 4H2O -----------> Si(OH)4 + 4 HCl

In carbon there is no vacant d -orbitals. Hence it can not increase its valency beyond four. Therefore tetrahalides of carbon are not hydrolysable.
The stability of dihalides of group 14 increases as we descend the group.

3. The elements of group 14 form two types of oxides, monoxides of the type MO and dioxides of the type MO2. All elements of group 14 except Si form monoxides. Among dioxides, CO2 exist as linear monomeric molecules because carbon froms Pie - Pie multiple bonds with oxygen (O=C=O). In all other dioxides, group 14 element and oxygen atoms are connected by single covalent bonds forming infinite three dimensional network structures. Hence they exist as solids.

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