In details

Covalent bond

Ion bonding explains how atoms of an element that loses electrons are joined to resemble a noble gas and another element that receives electrons to resemble a noble gas.

But how to explain the union between atoms of one or more chemical elements that need to receive electrons?

Let's look at the cases of substances H2, O2, N2, Cl2 and H2O. Looking for these elements in the periodic table we have:

Elementproton numbernumber of elementsTotal electrical charge
Hydrogen (H) 1 1 0
Nitrogen (N) 7 7 0
Oxygen (O) 8 8 0
Chlorine (Cl) 17 17 0

Compare the number of electrons in these atoms with that of the noble gases shown in the table on the previous page.

To resemble helium, hydrogen needs 1 more electron. To resemble neon, nitrogen needs 3 electrons and oxygen needs 2. And chlorine needs 1 electron to get the same number of electrons as the noble argon gas.

Chemists have proposed that in substances like H2, O2, N2, Cl2 and H2O, atoms are held together because their electrospheres share some electrons - enough to make them have a noble gas-like electrosphere. In the following representations, the black dots represent the electrons shared by atoms in forming these substances.

None of the atoms involved became an ion, meaning none of them lost or received electrons.

Because of the sharing, everyone has in their electrospheres the amount of electrons that make them resemble noble gases.

When atoms come together by sharing electrons, we say that between them a covalent bond is established. The groups of atoms joined by covalent bond They are called molecules.