We know that everything around us is made up of atoms. The atoms bind together with each other with the help of forces of attraction between them and form compounds. These forces of attraction arise from the interaction of the negatively charged electrons with the positively charged protons. When one atom is brought in the vicinity of another atom, the protons of the first atom attract the electrons of the second atom towards them. Similarly, the protons of the second atom attract the electrons the first one. Also, the protons in the nuclei of the atoms repel each other because they have the same positive charge. The electrons of the two atoms also try to push each other away because of the same reason. When the forces of attraction overcome the forces of repulsion, a chemical bond forms between the two atoms.
Electrons occupy the space around the atom in shells. They keep going around the nucleus in these shells. These can be thought of as circular orbits around the nucleus but that is a very crude approximation, which works for the purposes of visualization. Imagine an electron is moving around the nucleus in a shell, this hypothetical circular orbit. If it were to gain energy, it will be able to overcome the attraction which will it is being pulled by the proton and move to a position or shell which is further away. In such a case, electrons that occupy the final or the ultimate shell, the one which is the farthest from the nucleus, will have the most energy that is possible for an electron of that atom. These electrons are called valence electrons.
Sharing is caring
When two atoms come closer to each other, the nuclei of the atoms attract the valence electrons more strongly as compared to the inner electrons. A covalent bond is formed when a pair of valence electrons are shared between two atoms. This pair of valence electrons can be contributed by only one atom or the pair can be formed through donations by both the participating atoms. This bond formation leads to the creation of a molecule of a covalent compound. In such a molecule, the electron pair is attracted equally by the nuclei of the two atoms. This leads to very strong forces of attraction between the two atoms. In fact, covalent bonds are strongest of all bonds.
Types of covalent bonds
There are two types of covalent bonds as well. A single covalent bond between two atoms is called a sigma bond. A sigma bond is the strongest type of bond that can be formed between two atoms since of the two types of covalent bonds, it is the stronger one. When a sigma bond exists between two atoms and another bond forms, in order to form a double bond, the second bond is called a pi bond. Thus, a double bond will have one strong sigma bond and another bond which is a pi bond. Now, if a triple bond is formed between two atoms, it will consist of one strong sigma, one pi bond and another pi bond, for a total of two pi bonds.