Formal Charge (2) Introduction
Formal Charge (2) Introduction
Introduction
This video explains how to calculate the formal charge of atoms within molecules. It builds on the concept of free atom charge calculation by introducing shared electrons and their impact on formal charge.
Main Points/Arguments
- Formal Charge Definition:
- Formal charge is the charge on an atom within a molecule, calculated based on the number of valence electrons in the neutral atom and the number of bonding and non-bonding electrons.
- Formula for Formal Charge:
- Formal Charge = (Valence electrons in neutral atom) - (1/2 number of bonding electrons) - (Number of non-bonding electrons)
- This formula accounts for shared electrons in covalent bonds.
- Example 1: Methane (CH4):
- Carbon has 4 valence electrons.
- Each hydrogen shares a pair of electrons with carbon, so each hydrogen effectively has 1 electron.
- Formal charge for hydrogen: 1 - 1 = 0.
- Formal charge for carbon: 4 - (1/2 * 8) = 4 - 4 = 0.
- Example 2: CH3+:
- Formal charge for hydrogen remains 0.
- Carbon shares 6 electrons with hydrogens and has no non-bonding electrons.
- Formal charge for carbon: 4 - (1/2 * 6) = 4 - 3 = +1.
- Example 3: CH3-:
- Formal charge for hydrogen remains 0.
- Carbon shares 6 electrons with hydrogens and has 2 non-bonding electrons.
- Formal charge for carbon: 4 - (1/2 * 6) - 2 = 4 - 3 - 2 = -1.
Examples or Evidence
- Hydrogen Atoms:
- Hydrogen always has 1 valence electron.
- Formal charge calculation consistently shows 0 for hydrogen in these examples.
- Carbon Atoms:
- Different bonding situations (methane, CH3+, CH3-) demonstrate how shared and non-bonding electrons affect the formal charge.
- The formal charge helps assign the charge to specific atoms within a molecule.
Conclusion
Formal charge is an essential concept in chemistry for understanding the distribution of charge within molecules. The calculation formula takes into account both bonding and non-bonding electrons, providing a precise method to assign charges to individual atoms.