Write the important conditions required for the linear combination of atomic orbitals to form molecular orbitals.
The following are the conditions for the linear combination of atomic orbitals:
(i) The combining atomic orbitals should have comparable energies.
(ii) The combining atomic orbitals must have proper orientations (same symmetry) so that they are able to overlap to a considerable extent. For example, assuming 2-axis as molecular (or internuclear axis), allowed the combination of atomic orbitals are 2pz orbital of one atom can combine with 2pz orbital of another atom. On the other hand, 2pz orbital of one atom cannot combine with 2px or 2py orbital of another atom or 2px can not combine with 2py. Similarly, 2s orbital of one atom can combine with 2pz orbital but cannot combine with 2lpx or 2py orbital of another atom because they do not have proper orientation for the overlap.
(iii) The extent of overlapping should be large. Greater the overlap, greater will be the electron density.
Discuss in brief sp2 hybridization (hybridization in C = C bond). Discuss the molecular orbital structure of ethylene (first member of alkene).
Or
Draw diagrams showing the formation of a double bond between carbon atoms in C2H4.
Which hybrid orbitals are used by carbon atoms in the following molecules ?
(a) CH3 – CH3
(b) CH3 – CH = CH2
(c) CH3 – CH2 - OH
(d) CH3 - CHO
(e) CH3COOH
Write the significance of a plus and minus sign shown in representing the orbitals.
The orbital is the maximum probability of finding an electron around the nucleus. This probability is measured in terms of the wave function. The wave function can be positive or negative values.
Since orbitals are represented by wave functions, therefore a plus sign in an orbital represents a positive wave function and a minus sign represents a negative wave function. Further the wave functions of two 1s atomic orbitals can combine in two different ways:
(i) When both have the same signs.
(ii) When they have different signs.