A protonated Ammonium ion or NH4+ is made up of Nitrogen and Hydrogen. The ion is the by-product of a chemical reaction between a proton donor and Ammonia, which is as follows: NH3 + H+ ——> NH4+
Lewis Structure
Lewis Structure is a simplified arrangement and presentation of the electrons present in the valence shell of a molecule. A Lewis Structure is a depiction of the arrangement of electrons in the standalone atoms of an element. In the Lewis Structure, electrons are depicted as dots. A bond between two electrons is represented by a line marked by a dot at both ends, involving the participating electrons. The end goal is to identify a configuration with the best electron arrangement such that the formal charges and the octet rule are upheld. While understanding the concept of Lewis Structure, it is essential to keep in mind that the idea is neither to explain the molecular geometry nor of the formation of bonds nor of the electron sharing between two atoms of one or multiple elements.
What is the Lewis Structure of NH4?
As mentioned earlier, NH4+ is made up of Nitrogen and Hydrogen. If we look towards the periodic table, we will find Hydrogen in group 1. This means that Hydrogen has 1 electron. NH4+ has 4 hydrogen atoms, therefore, there are 4 hydrogen electrons. Nitrogen’s valence electron count, however, is 5, owing to its position in the 5th group of the periodic table. The plus sign denotes the absence of 1 electron; therefore, it is minus one. If we total out the number of electrons, it will be (1×4) + (5×1) – 1 = 4 + 5 – 1 = 8. We thus have 8 valence electrons here. Keeping Nitrogen in the center, and considering Hydrogen’s position on the outside, we can place the 4 hydrogen atoms surrounding the single nitrogen atom. Next is putting the chemical bonds. Since the NH4+ atom has 8 valence electrons, our arrangement will be according to 2,4,6, and 8. Referring to the octet rule, hydrogen needs only 2 valence electrons, which it already has. Even Nitrogen, which needs 8 electrons in the valence shell has all 8 of them, thereby forming a full exterior shell. The loss of an electron is depicted by putting a + sign enclosing the Lewis structure.
Molecular Geometry of NH4
While the Lewis Structure is a 2-dimensional depiction of an atom of a molecule, molecular geometry is the visualization and designing of the atoms in a 3-dimensional space. The concept of molecular geometry aims to depict the generic shape and structure of a molecule, accurate to the length between different bonds, the bond and torsional angles, other geometrical factors and variables that govern the shape and arrangement of an atom, and therefore, a molecule. Molecular geometry also helps to determine the atomic properties of an element, such as polarity, magnetism, reactivity, color, biological potency, and 3-dimensional space alignment. The properties of an atom identified through molecular geometry help in understanding the behavior, utility, and reactivity of the element. Depending upon their geometry, various molecular structures can be classified into linear, angular, trigonal planar, octahedral, trigonal pyramidal, among others. One can draw the 3-dimensional structure of an atom once they have the Lewis Structure of an atom. The 3-dimensional geometrical structure of ammonium, NH4+ is referred to as Tetrahedral. Nitrogen, having 5 valence shell electrons, along with 4 from Hydrogen, should have had 9 electrons. But the + sign decrees that NH4+ has 8 valence shell electrons, due to the positive ion. This means that NH4+ has 4 pairs in total, which are bonded due to the 4 atoms of hydrogen. Since NH4+ is a cation, the bond angle between 2 respective hydrogen atoms is 109.5 degrees instead of 90 degrees, which is as far away from one another as possible. A smart way to remember the structure of ammonium is that ‘tetra’ stands for four, that is the number of bond pairs nitrogen makes in Ammonia. While this makes the molecule symmetrical, it also makes it a non-polar molecule, as the bond polarity of each Nitrogen-Hydrogen bond cancels out. For better understanding, you can also refer to the already written article on the polarity of NH4. Below is the image of the geometrical representation of the NH4+ molecule.
The Hybridization of NH4
The concept of Hybridization decrees that atomic orbits fuse with one another to form new degenerated hybrid orbitals, which influence bonding properties and molecular geometry of the atoms of an element. It can be considered as an extension of the valence bond concept and lays its foundation on the molecular and quantum mechanics of an atom. These new orbitals may have different shapes, energies, etc. when compared to the previous ones. Hybridization brings about changes in the orbital arrangement of an atom as well. Such a structure arises from the need for a refined geometry of atoms necessary for electrons to pair up and thus, form different chemical bonds, as inducted by the valence bond theory. These hybrid orbitals, formed by the hybridization of an atom, are helpful in the explanation and understanding of an atom’s molecular geometry, its atomic bond properties, and the position in the atomic space. In most common scenarios, atomic orbitals with similar energy combine to form hybrid orbitals. While the exchange between atomic orbits of different atoms leads to the creation of molecular orbits, hybridization of an atom is assumed to be a combination of different atomic orbits, overlaying one another in different fractions. Atomic orbits of comparable levels of energy participate in forming hybrid orbitals. This process can also involve half-filled and fully filled orbitals as well, provided that the level of energy remains similar. During hybridization, the orbitals having similar energy can mix. Most common types of hybridizations are sp, sp2, sp3, sp3d, sp3d2, sp3d3 etc.
Ammonium ion formed by the release of an electron has 8 total electrons in the valence shell. In NH4+, nitrogen and the 4 hydrogen atoms make 4 sigma bonds, out of which 3 are covalent bonds and the fourth one is a dative bond. The NH4+ ion has no pi bonds. As a result, all four electrons contained in the atomic orbitals in the outermost shell of the nitrogen atom can participate in hybridization, making it SP3. Another way of identifying the hybridization of an atom is by the following formula: Hybridization = Number of Ion Pairs + Number of Sigma Bonds. Since Ammonium has 0 ion pairs and 4 sigma bonds, the hybridization value is 4. Therefore, the configuration of NH4+ is SP3.
Conclusion
The concepts of Lewis Structure, Molecular Geometry, and Hybridization hold great significance in understanding the structure, geometry, and subsequently the behavior of a substance, which is a direct result of the properties of associated element’s atoms. NH3, or commonly known as Ammonia is widely used as a fertilizer, refrigerant gas, water purification, and for industrial manufacture. Its conversion to Ammonium changes certain chemical properties and while the Lewis structure helps us to understand the 2-dimensional arrangement, molecular geometry sheds light on its structural properties. Hybridization provides the NH4+ atom stability, therefore giving it numerous advantageous uses.
