Ionic bond
Ionic bonds are a type of
chemical bond based on
electrostatic forces between two oppositely-charged ions. In ionic bond formation, a metal donates an electron, due to a low electronegativity to form a positive ion or cation. In ordinary
table salt, the bonds between the
sodium and chlorine ions are ionic bonds. Often ionic bonds form between
metals and non-metals. The non-metal atom has an
electron configuration just short of a noble gas structure. They have high electronegativity, and so readily gain electrons to form negative ions or anions.
Encyclopedia
Ionic bonds are a type of
chemical bond based on
electrostatic forces between two oppositely-charged ions. In ionic bond formation, a metal donates an electron, due to a low electronegativity to form a positive ion or cation. In ordinary
table salt, the bonds between the
sodium and chlorine ions are ionic bonds. Often ionic bonds form between
metals and non-metals. The non-metal atom has an
electron configuration just short of a noble gas structure. They have high electronegativity, and so readily gain electrons to form negative ions or anions. The two or more ions are then attracted to each other by
electrostatic forces. Such bonds are stronger than
hydrogen bonds, but similar in strength to
covalent bonds.
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Ionic bonding occurs only if the overall energy change for the reaction is favourable when the bonded atoms have a lower energy than the free ones. The larger the resulting energy change the stronger the bond.
Pure ionic bonding is not known to exist. All ionic bonds have a degree of
covalent bonding or
metallic bonding. The larger the difference in electronegativity between two atoms the more ionic the bond. Ionic compounds conduct
electricity when molten or in solution. They generally have a high melting point and tend to be soluble in water.
Polarization effects
Ions in
crystal lattices of purely ionic compounds are
spherical, but, if the positive ion is small and/or highly charged, it will distort the electron cloud of the negative ion. This
polarization of the negative ion leads to a build-up of extra charge density between the two
nuclei, i.e., to partial covalency. Larger negative ions are more easily polarized, but the effect is usually only important when positive ions with charges of 3+ are involved . However, 2+ ions or even 1+ show some polarizing power because their sizes are so small . The
Polarizing Power depends on the ratio of charge and size of the ion, often called the
charge density.
Ionic Structure
Ionic compounds in the solid state form a continuous ionic lattice structure in an
ionic crystal. When all the ions are approximately the same size, they can form a structure that is face-centered cubic, but, when the ions are different sizes, the structure is often
body-centered cubic. In ionic lattices the coordination number refers to the number of ions that each is connected, too.
Ionic versus covalent bonds
In an ionic bond, the atoms are bound by attraction of opposite ions, whereas, in a
covalent bond, atoms are bound by sharing electrons. In covalent bonding, the
molecular geometry around each atom is determined by
VSEPR rules, whereas, in ionic materials, the geometry follows maximum
packing rules.
Thus, a compound can be classified as ionic or covalent based on the
geometry of the atoms.
See also
External links
