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As a quantum-mechanical description, Pauling proposed that the wave function for a polar molecule AB is a linear combination of wave functions for covalent and ionic molecules: ψ = aψ(A:B) + bψ(A + B −). The amount of covalent and ionic character depends on the values of the squared coefficients a 2 and b 2. [4]
Thus sodium chloride (with a low positive charge (+1), a fairly large cation (~1 Å) and relatively small anion (0.2 Å) is ionic; but aluminium iodide (AlI 3) (with a high positive charge (+3) and a large anion) is covalent. Polarization will be increased by: high charge and small size of the cation Ionic potential Å Z+/r+ (= polarizing power)
As noted above, covalent and ionic bonds form a continuum between shared and transferred electrons; covalent and weak bonds form a continuum between shared and unshared electrons. In addition, molecules can be polar, or have polar groups, and the resulting regions of positive and negative charge can interact to produce electrostatic bonding ...
In organic chemistry, covalent bonding is much more common than ionic bonding. Covalent 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. [2] [3] The term covalent bond dates from 1939 ...
Thus, bonding is considered ionic where the ionic character is greater than the covalent character. The larger the difference in electronegativity between the two types of atoms involved in the bonding, the more ionic (polar) it is. Bonds with partially ionic and partially covalent character are called polar covalent bonds. For example, Na–Cl ...
Covalent bonds are generally formed between two nonmetals. There are several types of covalent bonds: in polar covalent bonds, electrons are more likely to be found around one of the two atoms, whereas in nonpolar covalent bonds, electrons are evenly shared. Homonuclear diatomic molecules are purely covalent.
The partial ionic bonding between the TTF and TCNQ molecules partially guides the organization of the crystal structure. The van der Waals interactions of the core for TTF and TCNQ guide adjacent stacked columns. [30] (a) A lewis dot structure and ball and stick model of TTF and TCNQ. The partial ionic bond is between the cyano- and thio- motifs.
Molecules, by definition, are most often held together with covalent bonds involving single, double, and/or triple bonds, where a "bond" is a shared pair of electrons (the other method of bonding between atoms is called ionic bonding and involves a positive cation and a negative anion).