What Is Formal Charge?, Formula, Examples, Important Points
What is Formal Charge? : Formal charge is a way to distribute electrons among atoms in a molecule or ion. It is a bookkeeping system that assigns an "imaginary" charge to each atom based on its valence electrons and the number of electrons it shares in a covalent bond.
Shrivastav 20 Dec, 2023
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Formal charge formula:
Formal charge formula : The formula for calculating formal charge is:
Examples Of Formal Charge:
Let us consider the ozone molecule (O3 ). The Lewis structure of O3 , may be drawn as:
The atoms have been numbered as 1. 2 and 3. The formal charge on :
The central O atom marked
The terminal O atom marked
The terminal O atom marked
Hence, we represent O
3
along with the formal charges as follows :
It's essential to note that formal charges do not imply actual charge separation within the molecule. Assigning charges to atoms in the Lewis structure primarily serves the purpose of monitoring valence electrons in the molecule. Formal charges play a key role in choosing the lowest energy structure among several potential Lewis structures for a particular species. Typically, the lowest energy structure is characterized by the smallest formal charges on the atoms.
Important Points To Remember
- The concept of formal charge is derived from a perspective rooted in pure covalent bonding, wherein electron pairs are presumed to be equally shared by adjacent atoms.
- A pair of formal charges, with one being +1 and the other -1 on neighboring atoms, is considered indicative of a coordinate bond.
- Lewis dot structure with minimum formal charges is the most stable.
- Lewis structures featuring negative formal charges on the more electronegative atom are favored over those with negative formal charges on the less electronegative atom.
- Lewis structures with unlike charges close together are more likely than Lewis structure with opposite charges widely separated. and similarly Lewis structures with like charges on adjacent atoms are very unlikely.
Formal Charge FAQs
Q1: What is the formal charge?
Ans. Formal charge is a concept used in chemistry to assign an electric charge to each atom within a molecule or ion. It helps in understanding the distribution of charges in a molecular structure.
Q2: Can formal charge predict the actual charge of an ion?
Ans. No, formal charge is a theoretical concept used for assigning charges in Lewis structures. It may not always accurately predict the actual charge observed in ions.
Q3: How is formal charge applied in determining resonance structures?
Ans. Formal charge aids in identifying and comparing resonance structures by evaluating the stability and distribution of charges in different resonance forms of a molecule.
Q4: Does a molecule with lower formal charges indicate greater stability?
Ans. Not necessarily. While lower formal charges can suggest a more stable structure, other factors like electronegativity and resonance also play a crucial role in determining the overall stability of a molecule.
Q.5: Can formal charge be zero for all atoms in a molecule?
Ans: Yes, in some cases, a molecule can have formal charges of zero for all its atoms, indicating a stable electron distribution.
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