Electron sharing in covalent bond

FIGURE 1 5 Counting electrons in nitnc acid The electron count of each atom is equal to half the number of electrons it shares in covalent bonds plus the number of electrons in its own unshared pairs... 

The great American scientist G. N. Lewis coined the word covalent, early in the 20th century. He wanted to express the way that a bond formed by means of electron sharing. Each covalent bond comprises a pair of electrons. This pairing is permanent, so we sometimes say a covalent bond is a formal bond, to distinguish it from weak and temporary interactions such as induced dipoles. 

Two or three electron pairs can also be shared in covalent bonds called double and triple bonds, respectively. A single atom of carbon forms a double bond with the oxygen... 

The carbon atom has 4 outer electrons, which are usually shared in covalent bonds that point to the vertices of a tetrahedron (a triangular pyramid). 

As we said above, bonds aren t always purely ionic or purely covalent. The best models for ionic bonds include some electron sharing. And covalent bonds don t always share electrons completely evenly. Any difference in electronegativity between bonding nuclei means that the electrons will be attracted more to one nucleus than the other. However, a bond could be considered purely covalent if it is between two identical nuclei, as in hydrogen gas, H2, or oxygen gas, O2. An extreme example of equality in electron sharing is the metallic bond. In a metal, all the atoms are identical and share electrons so readily that the metal can be thought of as one big molecule. 

When things are shared, like sharing the sofa with a friend, they are not always shared equally. This is also true of electrons involved in covalent bonds. At times the electrons involved in bonding are shared equally be-... 

OVERLAP OF CHARGE Shared electrons localized in Covalent bond... 

In compounds where bonding has covalent character, isomorphous substitution is prevented. This is because the need for electron sharing in the bond modifies structures away from the simple packing geometries predicted by the radius ratio rule. 

In this structure, four electrons (two electron pairs) are located between C and each O, and these electrons are shared in covalent bonds. Because a single bond is composed of two electrons (one electron pair) and because four electrons "bond" the carbon atom to each oxygen atom in this structure, there must be two bonds between each oxygen atom and the carbon atom, a double bond ... 

Electrons that can be shared in covalent bonding or lost to form cations in ionic compounds are called . All elements with the outer electron configuration ns np are . In respect to period number in the... 

Gilbert N. Lewis recognized the similarity in behavior of boron tri-fiuoride and a transferred proton toward a base, and in 1923 enunciated a definition of acid-base reaction in terms of sharing of an electron pair—fl base donates an electron pair in covalent bonding and an acid accepts the pair. The acid is called an ELECTROPHILE, and the base is called a nucleophile. In the base, the atom with the unshared pair of electrons is an electron-rich site, and, in the acid, the atom that accepts the pair of electrons to form a covalent bond is an electron-deficient site. The Lewis theory focuses attention on the electron pair rather than on the proton, and in so doing broadens the concept of acidity. The transferred proton of a so-called Brbnsted acid is a special case of a Lewis acid. 

We consider all of the valence electron pairs of the central atom—both those that are shared in covalent bonds, called bonding pairs, and those that are unshared, called nonbonding pairs or unshared pairs or lone pairs. 

Coordinate Covalent Bond n A covalent bond in which both shared electrons appear to have been contributed by one atom. (2) coordinate link, coordinate covalent bond, dative bond, semipolar bond, or dipolar bond is a description of covalent bonding between two atoms in which both electrons shared in the bond come from the same atom. The distinction from ordinary covalent bonding is artificial, but the terminology is popular in textbooks, especially those describing coordination compounds. Once such a bond has been formed, its strength and description is no different from that of other polar covalent bonds. An example of a dipolar bond in the ammonium ion. 

Electrons that can be shared in covalent bonding or lost to... 

In these two examples, we designated the electrons involved in bond formation differently—(x) from one atom and ( ) from the other. This helps to emphasize that an electron is transferred in ionic bonding and that a pair of electrons is shared in covalent bonding. Of course, it is impossible to distinguish between electrons, and henceforth we will use only dots ( ) to represent electrons in Lewis structures. In Lewis theory, we use square brackets to identify ions, as we did in equation (10.1). The charge on the ion is given as a superscript. 

The solution that has been devised for this problem is to imagine that the shared electron pairs in covalent bonds between different elements are completely transferred to one of the two bound atoms. The transfer is assumed to occur to the more electronegative of the two. 

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