Covalent compounds hybridization

The element before carbon in Period 2, boron, has one electron less than carbon, and forms many covalent compounds of type BX3 where X is a monovalent atom or group. In these, the boron uses three sp hybrid orbitals to form three trigonal planar bonds, like carbon in ethene, but the unhybridised 2p orbital is vacant, i.e. it contains no electrons. In the nitrogen atom (one more electron than carbon) one orbital must contain two electrons—the lone pair hence sp hybridisation will give four tetrahedral orbitals, one containing this lone pair. Oxygen similarly hybridised will have two orbitals occupied by lone pairs, and fluorine, three. Hence the hydrides of the elements from carbon to fluorine have the structures... 

Covalent compounds, arising from the attack of strong oxidizing systems, such as fluorine or Mn(VII), on graphite. The aromatic planarity of the graphite sheet is destroyed, and a buckled, sp -hybridized sheet is created. 

Tin has been observed in both valences +2 and 4 in which the —4 state represents the Xe configuration in which formally four electrons have been accepted (5s25p6). The sp3 hybridization to form tetrahedral covalent compounds can be discussed if one of the 5s electrons is promoted into the 5p orbital. When 5d orbitals are added to the hybridization, tin(IV) compounds with higher coordination numbers (of 5, 6, 7, 8) are formed. In general, tin(IV) is known to form compounds or complexes in which it adopts the coordination numbers 4 and 6, although compounds with numbers 2, 3, 5, 7 and 8 are... 

Some atoms, even in covalent compounds, carry a formal charge, defined as the number of valence electrons in the neutral atom minus the sum of the number of unshared electrons and half the number of shared electrons. Resonance occurs when we can write two or more structures for a molecule or ion with the same arrangement of atoms but different arrangements of the electrons. The correct structure of the molecule or ion is a resonance hybrid of the contributing structures, which are drawn with a double-headed arrow () between them. Organic chemists use a curved arrow (O) to show the movement of an electron pair. 

The direction of a chemical bond directly determines the structure of covalent compounds. For example, in diamond (its electron configuration being ls 2s 2p ), four hybrid sp orbitals are formed due to the destruction of a spin bond at s levels and the excitation of three electrons at p levels, they are directed from the centre to the vertices of regular tetrahedron. The angle between the axes of orbitals is equal to 109°28. ... 

For more covalent compounds, the best empirical correlation was obtained by taking into account the degree of oxygen s-p hybridization p, given by... 

In the metal derivatives of phthalocyanine the metal atoms are coordinated by four atoms of nitrogen at the corners of a square, and this arrangement suggests that these atoms are bound by covalent dsp2 hybrid bonds. Such an explanation is acceptable in the case of the transition metals, which readily form dsp2 bonds, but cannot account for the existence of the beryllium compound. It is, however, notable in this connexion that this derivative is conspicuously less stable than the phthalocyanines of the other metals. 

Beryllium chloride is a substance of low melting point, is non-conducting when in the molten state, and is soluble in many organic solvents. All these characteristics point to a covalent compound, but it is difficult to see how this is to result from a beryllium atom with a fully filled outer s orbital. X-ray studies have established that the molecule contains two linear Be—Cl bonds, of equal strength. The problem is solved with the introduction of a concept of hybrid orbitals. 

Boron has the structure ls22s22plx, and we know that it forms a covalent compound, boron trichloride experimental work shows that there are three equal strength B—Cl bonds in the molecule. A good explanation of this is that hybrid orbitals are formed from boron 2s, 2pv and 2pv orbitals. This is illustrated in Figure 15b. The hybrid orbitals lie in the same plane and are known as sn2 hybrids, since they are formed from one s and two p orbitals. Note that each of the hybrid orbitals will be only partly filled, since there are only three electrons of principal quantum number 2 to be allocated. The layout of the BC13 molecule is shown in Figure 15c. The calculated bond angle for sp2 hybrids is 120°, and this is confirmed experimentally. 

Why do we hybridize atomic orbitals to explain the bonding in covalent compounds What type of bonds form from hybrid orbitals, sigma or pi Explain. 

Since the classical paper of Paulii and Huggins [4], it has become usual to calculate the distances between the atoms in crystals of covalent compounds and elements by the addition of certain constants known as the / atomic radii. At present, this term is understood to mean the extent of an atom along the direction of a bond [5]. Bearing this point in mind, we can use tables Of tetrahedral covalent radii [5,6] to calculate bond lengths in sp hybrid compounds with tetrahedral coordinations, employing the well-known formula of Schomaker and Stevenson [7]... 

Boron is the first member of Group 13 elements. It is a non-metal and forms only covalent compounds. It exhibits an oxidation state +3 in all its compounds. The electron configuration of boron is ns np and boron is said to form three covalent bonds using sp hybrid orbitals. The compounds of boron are electron deficient and accept a pair of electrons (Lewis acids). The bonding in certain boron compounds is of considerable theoretical interest. 

The reaction of beryllium metal with aqueous acids yields hydrogen and ionic compounds, such as BeCl2 4 H2O. In BeCl2 4 H2O, water molecules are covalently bonded to Be ions, producing the complex cations [Be(OH2)4] that, together with the anions d , form the crystal lattice. In covalent compounds, Be atoms appear to use hybrid orbitals—sp orbitals in BeCl2(g) and sp orbitals in BeCl2(s) (Fig. 21-12). 

It also forms compounds known as carbonyls with many metals. The best known is nickel tetracarbonyl, Ni(CO)4, a volatile liquid, clearly covalent. Here, donation of two electrons by each carbon atom brings the nickel valency shell up to that of krypton (28 -E 4 x 2) the structure may be written Ni( <- 0=0)4. (The actual structure is more accurately represented as a resonance hybrid of Ni( <- 0=0)4 and Ni(=C=0)4 with the valency shell of nickel further expanded.) Nickel tetracarbonyl has a tetrahedral configuration,... 

The compounds of carbon and silicon with hydrogen would be expected to be completely covalent according to these models, but the dhectionality of the bonds, which is towards the apices of a regular tetrahedron, is not explained by these considerations. Another of Pauling s suggestions which accounts for this type of directed covalent bonding involves so-called hybrid bonds. 

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