9.1.1 The essence and characteristics of covalent bond Chemical bonding: A chemical bonding is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. The theory of chemical bonding consists of 1)The ionic bond theory,2)The metallic bond theory and 3)The covalent bond theory Theories development on molecular structure: Lewis theory (1916)->Valence bond theory(1927) >Molecular obital theory(1929)->Hybrid orbit theory (1931)->Valence shell electron pair repulsion theory (1940).… 1)The ionic bond theory, 9.1.1 The essence and characteristics of covalent bond Chemical bonding ： A chemical bonding is an interaction between atoms or molecules and allows the formation of polyatomic chemical compounds. The theory of chemical bonding consists of : 2) The metallic bond theory and 3) The covalent bond theory Theories development on molecular structure: Lewis theory (1916) → Valence bond theory(1927) →Molecular obital theory(1929) → Hybrid orbit theory (1931) → Valence shell electron pair repulsion theory (1940)……