The atom is the most crucial part of a chemical element, breaking which we find protons, electrons, and neutrons. They all play a key member in the formation of chemical bonds. Many scientists have incredibly contributed to different specialties of chemistry. One of them was American chemist, Gilbert N. Lewis who introduced the concept of electron dot structure in 1916. The article the atom and the molecule tell about the position of valence shell electrons in a chemical bond. The concept is also commonly referred to as Lewis structures or simply Lewis dot structures.
Lewis Dot Structure
The Lewis structure indicates the atom and its position in the model of the molecule using its chemical symbol. It also describes the chemical bonding between atoms present in the molecule. Mainly, the structure depicts the arrangement of the valence shell electrons of an element. An electron that is placed in the outermost shell of an atom is known as a valence electron. To determine the number of valence electrons, you can simply note down the Group number of the element from the Periodic Table. Lewis used lines to state a covalent bond between two electrons and each electron is denoted by a dot in the diagram.
Rules to Draw Lewis Structure
Firstly, check out the atomic number of each atom from the Periodic Table. Calculate the total number of valence electrons of the atoms present in a molecule. Take care of the octet rule where the ions or atoms should have eight electrons in their outermost valence shell (Duplet Rule: There is an exception in the case of Hydrogen that needs only two electrons to gain stability.) While representing the bonds, you should know about lone and bonded pairs. Choose the central atom by identifying the least electronegative atom. Arrange the remaining electrons to the terminal atoms
Note: The most important thing about the Lewis dot structure is that only valence electrons take part in chemical bonding.
Steps to Draw the Lewis structure of N2
Below is the electron dot structure for a Nitrogen molecule:
In the Periodic Table, Nitrogen is placed in Group 5 across Period 2. Thus, as per the electronic configuration of the element i.e. 2,5, it has five electrons in its outermost valence shell. As per the molecule N2, it has two atoms of Nitrogen. The total number of electrons present in the valence shell is 5 * 2 = 10e. Thus, 10 valence electrons need to be arranged in the structure to show the chemical bonding between two atoms of the Nitrogen molecule. Now, distribute valence electrons around the atoms of N2. Since you have 2 atoms of Nitrogen, assign the valence electrons using dots in a diagram to each atom-like 5 dots around each atom. Use symbol N to represent the atom. Both the atoms have the same electronegativity, there will be no central atom in the structure. Take care of bonding and non-bonding electron pairs that directly influence the geometry of the Lewis structure. Now, set up the covalent bond by writing both the Nitrogen atoms next to each other and draw a line to represent the bond. Each bond shows two valence electrons. This bond is knowns as a single bond. Show the remaining 3 electrons at the external side of each atom. To follow the octet rule (eight electrons per atom), each Nitrogen atom needs 3 more electrons i.e. 6 electrons to make the correct structure. After creating a single bond between the atoms, both atoms have 6 electrons each. As per the octet rule, still each atom needs two more electrons to complete its outermost shell. At present, each atom has 7 electrons. Finally, after sharing three pairs of electrons that make the distribution of 6 electrons in a bond, it is known as a triple covalent bond.
Hybridization of Nitrogen (N2)
There are two types of bonds which are widely used in Chemistry, sigma (σ) and pi (π) bonds. Both the bonds help to identify the type of hybridization by either forming head-to-head overlap or when 2p orbitals overlap.
Sigma bond is the first bond that is made with other atoms. A pi bond is made due to the presence of a second or third bond.
For nitrogen atom, the valence-shell electron configuration is 2s2 2px1 2py1 2pz1 where it shows that 1s and 1p orbitals are hybridizing to give a new set of two sp-orbitals. The setup results in N2 forming sp hybridization. sp hybridization includes overlapping of sp-orbitals on both the nitrogen atoms to form a σ bond. On the other side, the two p-orbitals on both the atoms each containing one electron give a π bond. The next head-to-head overlapping of p-orbitals each containing one electron gives one more π bond. From the above explanation of overlapping, you can conclude that a single bond, double bond, and triple bond corresponds to a σ bond, σ bond plus a π bond, and a σ bond plus two π bonds respectively.
Molecular Geometry of Nitrogen (N2)
To understand the molecular geometry of any molecule, learning its Lewis structure and hybridization is very important. As discussed above, N2 forms a triple covalent bond and sp hybridization. As mentioned above, the Lewis structure only tells about which atoms have lone pairs but, valence-shell, electron-pair repulsion(VESPER) predicts the shape of many molecules. Mainly, the VSEPR model focuses on the electron pairs around the central atoms. It also takes care of the steric number that is the number of regions of electron density surrounding the atom. Since each atom has steric number 2 by counting one triple bond and one lone pair, the diatomic N2 will be linear in geometry with a bond angle of 180°. Being a linear diatomic molecule, both atoms have an equal influence on the shared bonded electrons that make it a nonpolar molecule. For more detailed knowledge you can refer to the polarity of N2.
Molecular Orbital Diagram of N2
Molecular orbitals exist in molecules where each molecule has its electron configuration in terms of a sigma bond and pi bond. According to molecular orbital theory, it tells about magnetic nature, stability order, and the number of bonds in a molecule. When two orbitals are added, the result is stable bonding molecular orbital and when orbitals are subtracted, it is called unstable anti-molecular bonding (*) which has more energy than the latter one. Considering the energy level diagram, the configuration of N2 is σ1S2, σ 1S2, σ2S2, σ2S2, π2Px2, π2Py2, σ2Pz1.
Conclusion
In the Lewis structure of the N2 molecule, there is a formation of a triple covalent bond represented by three lines between two atoms of Nitrogen. The leftover two 2p orbitals become two π bonds and electrons making a pair between the nitrogen atoms will make a sigma bond. VSEPR model assumes that molecular geometry minimizes the repulsion between the valence electrons. In the configuration, it goes in increasing order from lower to higher-order energy level. To calculate the formula is Bond order= (Nb-Na)/2.
