Ionic Bond Or Electrovalent Bond

In this type of combination, there is a complete transfer of one or more electrons from one atom to another. The atom that transfers electrons gets positive charge and the atom that gains electrons gets negative charge. The strong electrostatic force acting between positive (+ve) and negative (-ve) ions, holds them together. The attraction that binds oppositely charged ions together is termed electrovalent bond or ionic bond.

For illustration let us consider the combination of sodium (Na) and chlorine (CI) atoms to form common salt, sodium chloride (NaCl). In this combination, an atom of Sodium (Na) transfers one outer most shell electron and becomes positive For illustration, let us consider the combination of sodium (Na) and sodium ion (Na+) and an atom of chlorine gains that one electron to complete its octet and becomes chloride negative ion (Cl-).

NA2, 8, 1      --------à Na+2, 8 + e-

Cl2, 8, 7 + e- ------à CI2, 8, 8

Na++Cl1- ------à Na+           CI- or Na1+Cl-1

Fig 5.1 Formation of Sodium Chloride

The attraction that binds (Na+) and (CI-) ions together is called electrovalent bond and the compound (NaCl) is called electrovalent compound or ionic compound.

IMPORTANT TO NOTE

The electrovalent bond is also known as ionic bond because electrovalent compounds when dissolved in water or melted produce ions and therefore, conducts electricity.

Another example of electrovalent bond, is the formation of magnesium oxide (MgO) from magnesium and oxygen. The magnesium (Mg) atom has two electrons in its valence shell. If these two electrons are lost, the (Mg) will become a di-positive ion (Mg+2), and the oxygen (O) atom gains these two electrons to complete its octet, and becomes di-negative ion (O-2). These two oppositely charged ions form electrovalent bond and the compound (MgO) is called electrovalent compound.

5.4.1 Characteristics of Ionic Compounds:

1.    In ionic bond, it is impossible to say that any two ions are bonded to each other to produce molecule, but in the crystals of ionic compounds, the appositively charged ions are mutually surrounded by each other in orderly’ arrangement. Thus ionic compounds are solids at room temperature.

2.    Ionic compounds have high melting and boiling points because of the strong electrovalent bonds existing between the ions.

3.    Ionic solids, do not conduct electricity as the ions are not free to move. Once an ionic compound is melted (fused) the ions are free to move and conduct electricity. Similarly, solutions of ionic compounds conduct electricity.

4.    Ionic compounds are usually soluble in polar solvents, i.e. solvents of high di-electric constant such as water. But ionic compounds are insoluble in non polar (organic) solvents. These solvents have low di-electric constant such as benzene, carbon tetrachloride, etc. They are mostly inorganic compounds.

 

 
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