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Covalent and ionic bonding form a continuum, with ionic character increasing with increasing difference in the electronegativity of the participating atoms. Covalent bonding corresponds to sharing of a pair of electrons between two atoms of essentially equal electronegativity (for example, C–C and C–H bonds in aliphatic hydrocarbons).
Molecular solids have low melting (T m) and boiling (T b) points compared to metal (iron), ionic (sodium chloride), and covalent solids (diamond). [4] [5] [8] [13] Examples of molecular solids with low melting and boiling temperatures include argon, water, naphthalene, nicotine, and caffeine (see table below).
Ionic bonding is a type of electrostatic interaction between atoms that have a large electronegativity difference. There is no precise value that distinguishes ionic from covalent bonding, but an electronegativity difference of over 1.7 is likely to be ionic while a difference of less than 1.7 is likely to be covalent. [21] Ionic bonding leads ...
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 ...
Formulas for network solids, like those for ionic compounds, are simple ratios of the component atoms represented by a formula unit. [3] Examples of network solids include diamond with a continuous network of carbon atoms and silicon dioxide or quartz with a continuous three-dimensional network of SiO 2 units.
[23] [24] Conversely, covalent bonds between unlike atoms often exhibit some charge separation and can be considered to have a partial ionic character. [22] The circumstances under which a compound will have ionic or covalent character can typically be understood using Fajans' rules , which use only charges and the sizes of each ion.
These differences, in turn, lead to dramatically different behavior of covalent and ionic compounds both in the solution and solid phase. [3] In the solid phase, ionic compounds, e.g. salts, are prone to formation of crystal lattices; in polar solvents, they dissociate into ions surrounded by solvate shells, thus rendering the solution highly ...
He estimated that a difference of 1.7 corresponds to 50% ionic character, so that a greater difference corresponds to a bond which is predominantly ionic. [3] 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 ...