The key difference between monovalent and divalent is that monovalent elements can remove or gain one electron in order to become stable, whereas divalent elements can remove or gain two electrons in order to become stable.
The terms monovalent and divalent can describe the valency of a chemical element. These two terms describe the number of electrons an atom can gain or lose to achieve a stable electron configuration.
CONTENTS
1. Overview and Key Difference
2. What is Valency
3. What is Monovalent
4. What is Divalent
5. Side by Side Comparison – Monovalent vs Divalent in Tabular Form
6. Summary
What is Valency?
Valency can be described as the maximum number of electrons an atom can lose, gain or share in order to become stable. When considering metals and nonmetals, the octet rule describes the most stable form of an atom. According to the octet rule, if the outermost shell of an atom is completely filled with eight electrons, that configuration is stable. This means if the s and p sub-orbitals are completely filled, having ns2np6, this electron configuration is stable. Generally, noble gas atoms have this type of electron configuration. This indicates that other chemical elements need to either lose, gain or share electrons in order to obey the octet rule. The maximum number of electrons involved in this stabilization process is called the valency of that atom.
For example, the number of electrons in the outermost orbital of sulfur is 6. In order to become stabilized, the number of electrons in the outermost orbital should be 8 (according to the octet rule). Sulfur must gain or share two more electrons from outside. Therefore, the valency of sulfur is 2.
However, transition elements can have different valencies. This is because transition metals can be stabilized by removing different numbers of electrons.
What is Monovalent?
The term monovalent means having a valency of one. Another term for this name is univalent, meaning, “valency=one”. Monovalent atoms can form a single chemical bond because these atoms can either lose or gain only one electron in order to become stable. Some atoms tend to share this single electron, forming a single covalent bond, e.g. most nonmetals. But some atoms tend to completely remove or gain an electron, forming an ionic bond, e.g. metals. Chemical elements in the group 1 of the periodic table (the alkali metals) are usually monovalent because they can only lose one electron that is in the outermost s orbital.
What is Divalent?
The term divalent means having a valency of two. Divalent atoms can form two chemical bonds because these atoms can either lose or gain two electrons in order to get a stable electron configuration. Some divalent atoms tend to form two single covalent bonds by sharing these two electrons with two different atoms. Some atoms tend to form a double bond with another atom by sharing these two electrons. However, group 2 metals in the periodic table tend to form ionic bonds with divalent anions by completely removing the two electrons that are in the outermost s atomic orbital.
What is the Difference Between Monovalent and Divalent?
The terms monovalent and divalent are adjectives that describe the valency of an atom. The key difference between monovalent and divalent is that monovalent elements can remove or gain one electron in order to become stable, whereas divalent elements can remove or gain two electrons in order to become stable. Moreover, chemical elements in group 1 of the periodic table (the alkali metals) are usually monovalent while elements in group 2 of the periodic table are divalent.
Below is a summary tabulation of the differences between monovalent and divalent.
Summary – Monovalent vs Divalent
The terms monovalent and divalent are adjectives that describe the valency of an atom. The key difference between monovalent and divalent is that monovalent elements can remove or gain one electron in order to become stable, whereas divalent elements can remove or gain two electrons in order to become stable.
Reference:
1. “Valence (Chemistry).” Wikipedia, Wikimedia Foundation, 1 Sept. 2020, Available here.
Image Courtesy:
1. “Electron shell 016 Sulfur” By Pumbaa (original work by Greg Robson) – Application: (generated by script) (CC BY-SA 2.0 UK) via Commons Wikimedia