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Only the elements in the 18th group (noble gases) remain as free atoms naturally. Any other element does not remain as a free atom. Except for noble gases, all other atoms share electrons and form bonds to fill their valance shell with eight electrons.
According to the octet rule, the elements in the 18th group have obtained a stable electron configuration.
The Octet rule means that the atoms tend to have eight electrons in their valance shell. When an atom obtains s2 p6 configuration in its valance shell, that means that the atom has filled its valance shell. With this configuration atoms become stable. If an atom has electrons less than eight in its valance shell, it shares electrons with other atoms and obtains octet configuration. This makes that atom stable.
Helium has stabilized with 1s2 electron configuration and all the other elements in group 18 have stabilized with s2, p6 configuration. Therefore, the noble gases generally do not form bonds. But, due to the large radius of the atom and the weak attraction from the nucleus, only Xe forms bonds with highly electronegative atoms.
All the other elements in the periodic table do not possess a stable electron configuration. They have unpaired electrons in their valance shell. Therefore, those atoms share electrons with other atoms. Here the unpaired electrons will be paired and the octet configuration is obtained. Thus, the atoms become stable and form bonds.
When atoms with unpaired electrons are close together, the two nuclei of the atoms attract the electron cloud of each other atoms. Then, the two atoms get closer together. Then, a repulsive force is formed between the two electron clouds and between two nuclei. When the attractive force is equal to the repulsive force, the orbitals in the two atoms with unpaired electrons, will overlap.
Then the unpaired electrons will be paired and a bond is formed. Therefore, there are two electrons in one bond. The electrons in the bond are mutual to each other. An energy is released when a bond is formed. To break this bond, an equal energy should be supplied.
The bonds formed between atoms are called intramolecular forces. There are four main types of intramolecular forces.
A covalent bond is formed when two orbitals in two atoms with unpaired electrons are overlapped each other. Then a molecular orbital is formed and the unpaired electrons are paired. Here both two atoms provide an equal number of electrons. If one electron is provided from each atom, one pair of electrons is formed, and that means a single bond. A covalent bond can be of two types according to its polarity.
If there is no electronegativity difference between the two atoms that contribute the electrons for a covalent bond, it is a non-polar covalent bond. In a non-polar covalent bond, the electrons in the bond are shared with both atoms symmetrically. Non-polar covalent bonds are formed between atoms that are the same element.
Examples:-
If there is an electronegativity difference between the two atoms that contribute the electrons for a covalent bond, it is a polar covalent bond. The formed bond is polar. The electrons in a polar covalent bond are attracted to the atom that has a higher electronegativity.
Therefore, the electron density of that atom is increased. Thus, that atom has a slightly negative charge (δ-). And the other atom with lesser electronegativity got a slightly positive charge (δ+).
Dative bond, also known as the coordinate covalent bond is a special type of covalent bond. The only difference is, that in a dative bond, the two electrons that form the bond are coming from the same atom. After the bond is formed, it is similar to a covalent bond.
To form a dative bond one atom should possess an empty orbital and the other atom should possess a lone pair of electrons. After the bond is formed the donor atom has a positive charge and the receptor atom has a negative charge.
Example:
There is a lone pair of electrons on the nitrogen atom in ammonia. This lone pair can be shared with an atom in group 13, in which there is an empty orbital.
When there is a very high electronegativity difference between two atoms, the atom with the lesser electronegativity will completely remove electrons and the atom with higher electronegativity take electrons completely.
This results in positively and negatively charged ions. Due to the static electric attraction force between the positively and negatively charged ions, the ionic bond is formed. If a metal has formed a bond with a non-metal, it is an ionic bond.
Negative ions cluster around positive ions and positive ions cluster around negative ions to form a three-dimensional lattice.
Metals remove electrons completely and form positively charged ions. The removed electrons remain in the surroundings of the positively charged ions. It is called that the positively charged ions are submerged in an electron sea. Due to the attraction force between the electrons and the positively charged ions, a metallic bond is formed.
Thus, a lattice is formed. However, any electron does not bond with a positive ion permanently. Electrons in the electron sea can freely move through the lattice. If the number of electrons present in the lattice is high, and the radii of the positive ions are low, the strength of the metallic bond is high.
As an example, the metals in the group 1 are soft metals compared to the group 2 metals. This is because group 1 elements contribute only one electron from one atom and the ionic radius is higher than group 2.
But, group 2 elements remove two electrons to the electrons sea and their ionic radius is also less than group 1. Therefore, group 2 elements form stronger metallic bonds.
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