Walter Heitler and Fritz London are credited with the first successful quantum mechanical explanation of a chemical bond ( molecular hydrogen) in 1927. While the idea of shared electron pairs provides an effective qualitative picture of covalent bonding, quantum mechanics is needed to understand the nature of these bonds and predict the structures and properties of simple molecules. The numbers of electrons correspond to full shells in the quantum theory of the atom the outer shell of a carbon atom is the n = 2 shell, which can hold eight electrons, whereas the outer (and only) shell of a hydrogen atom is the n = 1 shell, which can hold only two. Each hydrogen has a valence of one and is surrounded by two electrons (a duet rule) – its own one electron plus one from the carbon. In the diagram of methane shown here, the carbon atom has a valence of four and is, therefore, surrounded by eight electrons (the octet rule), four from the carbon itself and four from the hydrogens bonded to it. Lewis proposed that an atom forms enough covalent bonds to form a full (or closed) outer electron shell. An alternative form of representation, not shown here, has bond-forming electron pairs represented as solid lines. Multiple pairs represent multiple bonds, such as double bonds and triple bonds. Pairs of electrons located between atoms represent covalent bonds. He introduced the Lewis notation or electron dot notation or Lewis dot structure, in which valence electrons (those in the outer shell) are represented as dots around the atomic symbols. Lewis, who in 1916 described the sharing of electron pairs between atoms. The idea of covalent bonding can be traced several years before 1919 to Gilbert N. Langmuir wrote that "we shall denote by the term covalence the number of pairs of electrons that a given atom shares with its neighbors." ![]() The term covalence in regard to bonding was first used in 1919 by Irving Langmuir in a Journal of the American Chemical Society article entitled "The Arrangement of Electrons in Atoms and Molecules". Covalent bonding is implied in the Lewis structure by indicating electrons shared between atoms. ![]() Covalent bonding that entails the sharing of electrons over more than two atoms is said to be delocalized.Įarly concepts in covalent bonding arose from this kind of image of the molecule of methane. Thus, covalent bonding does not necessarily require that the two atoms be of the same elements, only that they be of comparable electronegativity. Covalency is greatest between atoms of similar electronegativities. thus a "co-valent bond", in essence, means that the atoms share " valence", such as is discussed in valence bond theory.Ģ, the hydrogen atoms share the two electrons via covalent bonding. The prefix co- means jointly, associated in action, partnered to a lesser degree, etc. In organic chemistry, covalent bonding is much more common than ionic bonding.Ĭovalent bonding also includes many kinds of interactions, including σ-bonding, π-bonding, metal-to-metal bonding, agostic interactions, bent bonds, three-center two-electron bonds and three-center four-electron bonds. For many molecules, the sharing of electrons allows each atom to attain the equivalent of a full valence shell, corresponding to a stable electronic configuration. The stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding. ![]() These electron pairs are known as shared pairs or bonding pairs. ![]() A covalent bond forming H 2 (right) where two hydrogen atoms share the two electronsĪ covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |