CHEMICAL PROPERTIES

Carbon

In the ground state, electronic configuration of carbon is 1s²2s²2p²:

p p

^s s

_{401 kJ}

In this state it forms three covalent bonds, two of which are formed according exchange mechanism, and one on donor-acceptor (such bond is in CO). But carbon rarely is bivalent. Excitation of its atoms occurs easily and forms a state with 4 unpaired electrons. Energy required for atom excitation is exceeded by the energy released at formation of two additional covalent bonds. A difference between s- and p-electrons is taken off by sp- sp²- or sp³-hybridization, to which is undergone an atom of carbon depending on a partner in chemical bond. Therefore, mostly carbon behaves like fourvalent element. As d-orbitals in it are absent, its maximal valence is also 4.

Identical number of valence electrons and valence orbitals takes place only at two elements - hydrogen and carbon. For this reason they can form the greatest number of compounds between itself and with other elements.

kJ·mol^-1

It predetermines extraordinary abundance and variety of derivatives of carbon. From heterobonded atoms of carbon most widespread are C—H as a result of their large strength (441,2 kJ/mol). Carbon is also able to form multiple bonds.

With EN=2,5 carbon is an intermediate between electropositive and electronegative elements, although it is nearer to the last. Therefore even at the maximal polarization of atoms in its compounds there are no free ions C⁴⁺ and C^4-. Effective charges on atoms of carbon in all known compounds are considerably less then 1, that is compounds of carbon are weak polar.

In the simple substances carbon has already used its valence electrons, creating polymeric structures of diamond or graphite. Therefore in its crystalline forms carbon is absolutely chemically inert.

From this, regardless of modification, carbon has neither a taste nor smell, it is extraordinarily heavily melted and evaporates, it does not dissolve in all ordinary solvents. It is well dissolved in many molten metals (Fe, Co, Ni, the Pt metals) only, and at cooling it is again crystallized in the form of graphite.

Its chemical activity rises at transition from the diamond to amorphous carbon, which can be ignited in the atmosphere of oxygen at comparative slight heating:

С + О₂ = СО₂ DН°₂₉₈ = –395 kJ/mol

With a fluorine an amorphous carbon interacts already at ordinary conditions:

C + 2F₂ = CF₄

At high temperatures carbon reacts with metals, N₂, O₂, S, Si, B, with oxides of metals and salts, for example:

C + 2S = CS₂

C + CuO = Cu + CO

Date: 2016-01-03; view: 777