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An ionic bond (or '''electrovalent bond''') is a type of Chemical Bond based on Electrostatic Force s between two oppositely-charged Ion s. 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 (NaCl), the bonds between the Sodium and Chloride ions are ionic bonds. Often ionic bonds form between Metal s 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 Anion s. The two or more ions are then attracted to each other by Electrostatic Forces . : : 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 Bond ing or Metallic Bond ing. 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 Ion s in Crystal Lattice s of purely ionic compounds are Spherical ; however, 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+ (e.g., Al3+) are involved (e.g., pure AlCl3 is a covalent molecule). However, 2+ ions (Be2+) or even 1+ (Li+) show some polarizing power because their sizes are so small (e.g., LiI is ionic but has some covalent bonding present). IONIC STRUCTURE
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. ELECTRICAL CONDUCTIVITY See Also: Electrolyte Ionic substances in solution conduct electricity because the ions are free to move and carry the electrical charge from the anode to the cathode. Ionic substances conduct electricity when molten because atoms (and thus the electrons) are mobilised. Electrons can flow directly through the ionic substance in a molten state. SUBSTANCES IN IONIC FORM
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