Hydrogen atom is exception to the octet rule as it need only two valence electron in its outershell to complete the octet. And the nitrogen atom has 5 valence electrons in its outermost shell and it needs 3 more electrons to complete the octet and attains stability.
Therefore, both hydrogen and nitrogen atoms will share the electrons with each other to completing the octet and due to this, a bond is formed between them which is called a covalent bond. As we see in the above picture of covalent bond formation in NH3, the nitrogen atom has 5 valence electron in its outermost shell and it needs 3 more to complete the octet, hence, 3 hydrogen atom shares one electron each with the nitrogen atom. In this process, 3 hydrogen atom and one nitrogen atom completed their octet as the nitrogen atom gets 8 electrons in its outer shell and each hydrogen gets 2 electrons in their octet shell.
So, every atom in the NH3 molecule completed its octet by sharing electrons, hence, makes a covalent bond. Therefore, we can say ammonia NH3 has a three covalent bond N-H that contains 6 shared pairs of electrons or bonded pairs of electrons. Note: NH3 molecule also contains 2 lone pairs of electrons but they never take part in the formation of covalent bond, only shared electrons are used to makes a covalent bond.
After all, the covalent bond is made between the two atoms that share the electrons with each other. The NH3 molecule is not an ionic compound because the difference in electronegativity value between nitrogen and a hydrogen atom is not big enough to make an ionic bond between them according to the Pauling scale.
So, the difference in electronegativity in the N-H bond is less than 1. Also, the main difference in ionic or covalent is that an ionic bond is formed when either donating or accepting the electrons occurs between two atoms, and a covalent bond is formed when only sharing of electrons occurs between two atoms.
The nitrogen and hydrogen atoms in the NH3 molecule can never transfer their electrons because their octet can be completed only when they share the electrons with each other, hence, the bond formed in the NH3 molecule is covalent in nature rather than ionic.
A pure covalent bond is mostly formed in the molecule that has the same type of atoms and the same electronegativity, for example — O2, F2, Cl2, etc. Basically, a homonuclear molecule has the ability to form a pure covalent bond because the electronegativity of atoms is the same, hence, sharing of electrons is also equal in them.
In short, a pure covalent bond is formed between the atoms when they share an equal number of electrons. So, Is NH3 a pure covalent compound? No, NH3 is a not pure covalent compound because it is a heteronuclear molecule that contains different types of atoms nitrogen and hydrogen atom , and their electronegativity is also not the same.
The electronegativity for hydrogen is 2. So, the electrons are more shared towards the nitrogen atom as it is higher electronegative than the hydrogen atom, hence, unequal sharing of electrons occurs between nitrogen and hydrogen atoms.
So, the bonds formed in the NH3 molecule are not a pure covalent bond, hence, NH3 is not a pure covalent compound. A polar covalent compound is formed when the unequal sharing of electrons occurs between two atoms because of their difference in electronegativity value.
When the difference of electronegativity value between two atoms lies in between 0. A nonpolar covalent compound is formed when the equal sharing of electrons occurs between two atoms because of the very little difference in their electronegativity value.
When the difference of electronegativity value between two atoms is less than 0. So, Is NH3 a polar covalent or nonpolar covalent compound? NH3 is a polar covalent compound because the electronegativity difference between nitrogen and a hydrogen atom is 0. Also, the unequal sharing of electrons occurs in NH3 molecules because nitrogen 3. The separation of charges generates the dipole moment directed from positive to negative, hence, due to all these a bond is formed between nitrogen and hydrogen, which is called a polar bond.
This is because nitrogen and hydrogen are nonmetals in nature, that makes them more prone to sharing the electron with each other, also, the transferring of electrons cannot take place between nitrogen and hydrogen atoms because for competing the octet they need to share the electrons as both atoms have incomplete octet shell. The nitrogen atom is more electronegative than hydrogen, hence, it attracts more electrons towards itself. In Ammonia molecules three atoms of hydrogen form a covalent bond by sharing 3 electrons of nitrogen and hydrogen atoms leaving behind one lone pair on the nitrogen atom.
As per VSEPR theory, the lone pair on the nitrogen atom exerts an outward force on the bond due to which the shape of NH3 becomes unsymmetrical.
Lone pair-bond pair repulsion drives this force on the bonds. And the calculated electronegativity of Nitrogen is 3. Therefore, the difference in their electronegativities causes three dipole moments from the three N-H bonds in one direction.
The three dipoles in one direction form a net dipole moment that determines the NH3 polar molecule. In the N-H bond, Nitrogen being more electronegative pulls the electron pair slightly towards itself and becomes partially negatively charged. Ammonia gas is highly soluble in water forming ammonium ions and it should be noted that polar molecules get more easily mixed with another polar molecule.
And as we know that water is also a polar molecule. Therefore ammonia and water attract each other and get easily mixed. It is important to know the fact that apart from this polarity factor, they have an extra booster of attraction that is known as hydrogen bonding. As discussed above, Ammonia forms three bonds with hydrogen atoms leaving behind a single lone pair on the nitrogen atom. The overall shape of the NH3 molecule comes out to be Trigonal Pyramidal.
If we describe the position of the atoms, the nitrogen is a central atom with asymmetric charge distribution and having three bonds and one lone pair. These N-H bonds are arranged in a tetrahedral shape. The bond angle of N-H in the NH3 molecule is around Below is the lewis structure of the Ammonia molecule for better understanding. Electronegativity : In a covalent molecule, if two atoms forming a bond have different electronegativities, they disperse unequal charge on them resulting in the polarity of the bond.
And it should be understood that the greater the difference between the electronegativities of both atoms, the greater is the polarity of the bond. Dipole moment : it is a measure of the polarity of the bond between two atoms. It is calculated as follows.
Mathematically, the dipole moment of a molecule is the product of the charge over the atoms and the distance between them. Geometry : The molecular structure of a complete also depicts its polarity because symmetrical compounds are nonpolar in nature.
Whereas the molecules that are distorted or asymmetrical in shape tend to be polar. Basically, in symmetrically shaped molecules, the dipole moments within the molecule get canceled out of each other. The dipole moment is a vector value that has direction as well as magnitude. Ammonia being an asymmetrical molecule having three hydrogen atoms and one nitrogen forms the tetrahedral geometrical structure. The electronegativity difference between nitrogen and hydrogen makes the N-H bond polar and all the dipole moments of N-H bond constitute a net dipole moment of Ammonia molecule making it a polar molecule.
However, neither of these two models show any electronic details of how the covalent bond is formed. Website What next? Recommend next: The covalent bonding in the methane molecule. Explaining the properties of small covalently bonded molecules.
S ub-index for Part 3. Index for ALL chemical bonding and structure notes. Use My Google search box. Website map buttons below. Doc Brown's Chemistry. Transition Metals.
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