Concept of electrovalent(ionic) bonding

 Electrovalent bond is a chemical bond formed as a result of the transfer of one or more electrons from one atom to another. Electrovalent bonds are only formed between metal atoms and non-metal atoms.

When an atom involved in a chemical bond formation completely transfer the electrons from it outermost valence shell to another atom that acquires the electron into it valence shell an electrovalent bond is formed. The atom that loses the electron will become positively charged while the atom that gains the electron will become negatively charged. Electrovalent bonds are otherwise known as ionic bonds because the resulting loss and gain of electrons will lead to the formation of cations and anions. The nature of the bonding in the compound called table salt (or sodium chloride) is a very common example of electrovalent bonding which will be used as a means of our explanation. But before we examine the nature of electrovalent(ionic bonding), let first remind ourselves of why atoms form bonds in the first place.

Why atoms form bonds? During chemical reactions, atoms bond with each other in order to gain a stable arrangement of outer-shell electrons, like the atoms of Group 0. In other words, they bond in order to gain 8 electrons in their outer shell (or 2, if they have only one shell).

How sodium and chlorine atoms bond together

A sodium atom has just 1 electron in its outer shell. To obtain a stable outer shell of 8 electrons, it must lose this electron to another atom, making it become a sodium cation according to the equation below.

Na  → Na⁺     + e^-

At the other hand, a chlorine atom has 7 electrons in its outer shell. It can reach 8 electrons and complete it outermost shell by accepting just 1 electron from another atom. Doing so will makes it becomes a chloride anion: The chloride ion has a charge of -1 so it is a negative ion. Its symbol is Cl^-

 As we can see, a sodium atom must lose one electron, and a chlorine atom must gain one, to obtain stable outer shells of 8 electrons. So when a sodium atom and a chlorine atom react together, the sodium atom loses its electron to the chlorine atom, and two ions are formed. Here, sodium electrons are shown as 'o' and chlorine electrons as 'ӿ'

The two ions have opposite charges, so they attract each other. The force of attraction between them is strong. It is called an ionic bond. The ionic bond is the bond that forms between ions of opposite charge.

Structure of ionic bond of sodium chloride

When sodium reacts with chlorine, billions of sodium and chloride ions form. But they do not stay in pairs. They form a regular pattern or lattice of alternating positive and negative ions, as shown below. The ions are held together by strong ionic bonds.

The lattice grows to form a giant 3-D structure. It is called ‘giant’ because it contains a very large number of ions. This giant structure is the compound sodium chloride, or common salt. Since it is made of ions, sodium chloride is called an ionic compound. It contains one Na⁺ ion for each Cl^- ion, so its formula is NaCl. The charges in the structure add up to zero: the charge on each sodium ion is 1⁺ the charge on each chloride ion is 1^- total charge = 0 So the compound has no overall charge.

Sodium is a metal. Chlorine is a non-metal. They react together to form an ionic compound. Other metals and non-metals follow the same pattern. A metal reacts with a non-metal to form an ionic compound. The metal atoms lose electrons. The non-metal atoms gain them. The ions form a lattice. The compound has no overall charge. Another example of electrovalent bonding in compound is magnesiumOxide MgO.