The key difference between valency and charge is that valency indicates the ability of a chemical element to combine with another chemical element, whereas charge indicates the number of electrons gained or removed by a chemical element.
Valency and charge are closely related terms as both these terms describe the reactivity of a chemical element. Valency is the combining power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with. On the other hand, a charge of an atom is the number of protons minus the number of electrons in an atom.
CONTENTS
1. Overview and Key Difference
2. What is Valency
3. What is Charge
4. Side by Side Comparison – Valency vs Charge in Tabular Form
5. Summary
What is Valency?
Valency is the combining power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with. It is a measure of the reactivity of a chemical element. However, it only describes the connectivity of atoms and does not describe the geometry of a compound.
We can determine the valency by looking at the position of the chemical element in the periodic table. The periodic table has arranged the chemical elements according to the number of electrons in the outermost shell of the atom. The number of electrons in the outermost shell determines the valency of the atom as well. For example, group 1 elements in the periodic table have one outermost electron. Therefore, they have one electron for the displacement or the combination with a hydrogen atom. Thus, the valency is 1.
Figure 01: Periodic Table of Elements
Also, we can determine the valency using the chemical formula of a compound. The basis of this method is the octet rule. According to the octet rule, an atom tends to complete its outermost shell by either filling up the shell with electrons or by removing the extra electrons. For example, if we consider the compound NaCl, the valency of Na is one because it can remove one electron it has in the outermost shell. Similarly, the valency of Cl is also one because it tends to gain one electron to complete its octet.
However, we should not be confused with the terms oxidation number and valency because oxidation number describes the charge an atom can carry with it. For example, the valency of nitrogen is 3, but the oxidation number can vary from -3 to +5.
What is Charge?
A charge is the number of protons minus the number of electrons in an atom. Usually, these two numbers are equal to each other, and the atom occurs in neutral form.
Figure 02: Charge of a Hydrogen Atom
However, if an atom has an unstable electron configuration, then it tends to form ions by either gaining or removing electrons. Here, if an atom gains electrons, then it gets a negative charge since an electron has a negative charge. When an atom gains an electron, there aren’t enough protons in the atom to balance this charge; thus, the charge of the atom is -1. But, if the atom removes an electron, then there is one proton in extra; thus, the atom gets +1 charge.
What is the Difference Between Valency and Charge?
Valency indicates the reactivity of an atom, while charge indicates how an atom has reacted. So, the key difference between valency and charge is that valency indicates the ability of a chemical element to combine with another chemical element, whereas charge indicates the number of electrons either gained or removed by a chemical element.
Moreover, the value for valency has no plus or minus signs, while the charge has plus sign if the ion has formed by removing electrons and has the minus sign if the atom has gained electrons.
The below infographic summarizes the difference between valency and charge.
Summary – Valency vs Charge
Valency gives the reactivity of an atom while charge describes how an atom has reacted. In summary, the key difference between valency and charge is that valency indicates the ability of a chemical element to combine with another chemical element, whereas charge indicates the number of electrons a chemical element gains or removes.
Reference:
1. Helmenstine, Anne Marie. “What Is Valence or Valency?” ThoughtCo, Mar. 21, 2019, Available here.
Image Courtesy:
1. “Periodic Table Of Elements” By Dmarcus100 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Ions” By Jkwchui – Own work (CC BY-SA 3.0) via Commons Wikimedia