The changes are brought in the elemental semiconductors Si and Ge by replacing them with II-VI and III-V binary analogs or their ternary analogs I-III-VI2 chalcopyrides and II-IV-V2 pnictides respectively. Such compounds exhibit transitions from their parent compound in terms of nature of band gaps (Eg) as indirect to direct in addition to the changes in the values of the Eg. These changes have direct consequence in their optical properties with degenerate states being lifted leading to crystal field splitting and so on. The Eg in ternary bulk semiconducting materials is engineered as a function of certain structural parameters such as anion position parameter (u), tetragonal compression parameter (η) through effective alloying. The contributions to Eg due to these effects are studied as band gap anomalies. The present paper discusses the results of the band gap engineering in some of the bulk ABC2(A= Cd; B=Si,Ge,Sn; C= P,As) semiconductors using theoretical methods. The influence of each of A, B and C atom is also discussed. The dependence of morphology of nano semiconducting particles and the band gap on the chemical environment, temperature is reported by us. The confinement energy of a compound which is the difference in energy between the bulk and nano forms is investigated.