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Elements that are unstable usually combine with other elements either by losing, gaining, or sharing electrons. This is said to be chemical bonding. Usually, elements combine with others only with the help of valence electrons. Valence electrons are those that are present in the outermost shell of an atom. These are far from the nucleus and can easily be involved in bonding with other elements.
Elements combine by losing electrons or gaining electrons, which is the transfer of electrons. This type of bonding is called ionic bonding, which occurs between the elements with different electronegativity or between a metal and a nonmetal. Elements with almost the same electronegativity or with less electronegativity difference form covalent bonding by sharing electrons.
Hybridisation:
Hybridization is the phenomenon of intermixing of atomic orbitals of the central atom that differ slightly in energy and their re-distribution to an equal number of hybrid orbitals of equal shape and energy. hybridization occurs in the central atom only. In a covalent molecule, the element that has high valency is considered the central atom.
Purpose of hybridisation:
hybridization occurs in covalent molecules and between the atomic orbitals of the central atom. hybridization does not occur in all covalent molecules but occurs in heteroatomic molecules like methane, ammonia, etc. Hybridization occurs in the central atom, where the electrons in the valence shell exist in orbitals of different energy and shape.
Importance of hybridisation:
hybridization occurs in the central atom to get orbitals having equal energy, and the overlapping of orbitals with equal energy is effective. Hybridization helps in knowing the types of bonds formed between the two elements. The types of bonds formed between the covalently bonded atoms can be of two types: sigma bond and pi bond.
Sigma bond: Sigma bond is a covalent bond formed by sharing electrons present in the orbitals. The type of overlapping observed between the orbitals is head-on overlapping or inter-axial overlapping. This type of overlapping leads to a strong overlapping of orbitals. Hence, a stronger bond is formed that is stable with minimum energy.
Pi bond: Pi bond is also a covalent bond formed by sharing electrons present in the orbitals. The type of overlapping observed between the orbitals is sideways overlapping or parallel overlapping. Sideways overlapping leads to a weaker bond with high energy and less stability.
A sigma bond is a stronger bond and can exist independently, but a pi bond is a weaker bond and cannot exist independently.
Hybridization of nitrate:
The nitrate ion has the formula(NO3-). This ion is the negative part of many nitrate salts of alkali and alkaline earth metals. Examples include potassium nitrate, magnesium nitrate, calcium nitrate, etc. In the molecular nitrate ion, the nitrogen atom is the central atom. Though the oxygen atom is present, nitrogen is the central atom because it has less electronegativity than O, which means the tendency to lose electrons is higher than O and has greater valency than N.
In the nitrate anion, the N atom has a +5 oxidation state, and oxygen shows a -2 oxidation state. Nitrogen is the first most electronegative element, and oxygen is the second most electronegative element. Nitrogen is more electropositive compared to oxygen. Nitrogen is surrounded by three oxygen atoms and bonded by sharing electrons to form covalent bonds.
The hybridization of the central atom N is said to be sp2 hybridisation. The formula to calculate the hybridization of an element is the sum of several bond pairs and the number of lone pairs.
In the nitrate molecular ion Lewis dot structure, nitrogen is surrounded by three sigma bonds and zero lone pairs and has an octet configuration. Each oxygen gets eight electrons and satisfies the octet configuration.
Nitrogen atomic number – 7
Electronic configuration – 1s2 2s2 2p3
Nitrogen uses its 2s,2px,2py,2pz orbitals and forms 3 sp2 hybrid orbitals. Nitrogen overlaps with the p orbital of each oxygen with three sp2 hybrid orbitals. The unhybridised p orbital left in nitrogen overlaps sideways with the p orbital of an oxygen atom and forms a pi bond between N and O. The hybridization of N is said to be sp2. According to the VSEPR theory, for compounds with sp2 hybridisation, geometry is trigonal planar, and the bond angle is 120 degrees.
In a nitrate molecule, nitrogen has three oxygen atoms surrounded in the form of three corners of a triangle. All the atoms in the molecule are in one plane, and the molecule is said to be planar. In nitrate ion, nitrogen is bonded to oxygen by a double bond and has one pair on oxygen and a negative charge on oxygen. This negative charge does not reside only on one atom but moves throughout the molecule to all atoms and undergoes resonance and gets stabilised by resonance energy.
