The key difference between hypervalent and hypovalent compounds is that hypervalent compounds contain a central atom with more than eight electrons in the valence electron shell whereas hypovalent compounds contain a central atom with less than eight electrons in the valence electron shell.
The terms hypervalent and hypovalent refer to inorganic covalent compounds containing a central atom. These two types of compounds differ from each other depending on the number of electrons in the central atom – hypervalent compounds have a complete octet while hypovalent compounds do not.
CONTENTS
1. Overview and Key Difference
2. What are Hypervalent Compounds
3. What are Hypovalent Compounds
4. Side by Side Comparison – Hypervalent vs Hypovalent Compounds in Tabular Form
5. Summary
What are Hypervalent Compounds?
Hypervalent compounds are chemical species containing a central atom having more than eight electrons in the valence electron shell. We call it an expanded octet as well. The first scientist who defined this type of molecules is Jeremy I. Musher, in 1969. There are several classes of hypervalent compounds such as hypervalent iodine compounds, noble gas compounds like Xenon compounds, halogen polyfluorides, etc.
Figure 01: Hypervalent Compounds
The chemical bonding in hypervalent compounds can be described based on the molecular orbital theory. For example, if we take the sulfur hexafluoride compound, it has six fluorine atoms bonded to one sulfur atom via single bonds. Therefore, there are 12 electrons around the sulfur atom. According to molecular orbital theory, the 3s orbital, three 3p orbitals and six 2p orbitals from each fluorine atom contribute to the formation of this compound. Therefore, there is a total of ten atomic orbitals involved in compound formation. According to the electron configurations of sulfur and fluorine, there’s room for 12 valence electrons. Since there are 12 electrons, the sulfur hexafluoride compound is a hypervalent compound.
What are Hypovalent Compounds?
Hypovalent compounds are chemical species containing a central atom with less than eight electrons in the valence electron shell. Therefore, these are named as electron-deficient species. Unlike hypervalent compounds, almost all the hypovalent compounds are non-ionic species. Hence, they are mostly powered or granular compounds.
Figure 02: Boron Trifluoride is a Hypovalent Compound
These covalent compounds do not bear more than four single covalent bonds around them since four covalent compounds refer to eight electrons. In addition, the shapes of the covalent compounds are mostly linear or trigonal planar.
What is the Difference Between Hypervalent and Hypovalent Compounds?
The key difference between hypervalent and hypovalent compounds is that hypervalent compounds are chemical species containing a central atom with more than eight electrons in the valence electron shell, whereas hypovalent compounds are chemical species containing a central atom with less than eight electrons in the valence electron shell. Moreover, most hypervalent compounds are ionic species, while almost all hypovalent compounds are covalent compounds.
Furthermore, the shapes of covalent hypervalent compounds are either tetragonal or more complex structures, while hypovalent compounds cannot form complicated structures; they are either linear or trigonal planar. Thus, this is also a significant difference between hypervalent and hypovalent compounds. Besides, there are more than four covalent bonds around the central atom of hypervalent compounds but there are two or three covalent bonds around the central atom of hypovalent compounds.
Summary – Hypervalent vs Hypovalent Compounds
The terms hypervalent and hypovalent describe inorganic covalent compounds containing a central atom. The key difference between hypervalent and hypovalent compounds is that hypervalent compounds are chemical species containing a central atom with more than eight electrons in the valence electron shell, but hypovalent compounds are chemical species containing a central atom with less than eight electrons in the valence electron shell.
Reference:
1. “Hypervalent Molecule.” Wikipedia, Wikimedia Foundation, 18 Jan. 2020, Available here.
Image Courtesy:
1. “Hypervalency Gamma calculations” By Marcus durrant – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “BF3-Lewis” By Jcwf at Dutch Wikibooks (CC BY-SA 2.5) via Commons Wikimedia