What does UE stand for in the formal charge formula?

What does UE stand for in the formal charge formula?

• A. Number of valence electrons
• B. Bond energy
• C. Number of unshared electrons
• D. Electrons shared in covalent bonds

Answer: (C)

The main idea here is knowing what parts of an atom’s electron count are used in the formal charge calculation. In that formula, electrons are split into two groups: unshared (lone) electrons that aren’t involved in bonds, and electrons that are shared in covalent bonds. UE stands for the unshared electrons, the lone pairs on the atom. Formal charge is computed as the atom’s valence electrons minus the electrons assigned to it in the Lewis structure. Those assigned electrons include all unshared electrons (counted fully) plus half of the electrons involved in bonds (since bonding electrons are shared with another atom). So the commonly used expression is: FC = valence electrons − (unshared electrons + half of bonding electrons). For example, in a molecule like water, oxygen has valence 6, it carries 4 unshared electrons (two lone pairs), and there are 4 electrons in bonds (two O–H bonds). The formal charge would be 6 − (4 + 2) = 0, showing how the unshared electrons contribute fully to the count. If there were more unshared electrons, the formal charge would become more negative; if fewer, more positive. Choices about valence electrons or bond energy don’t match UE, and electrons shared in bonds are the bonding electrons, not the unshared ones.

The main idea here is knowing what parts of an atom’s electron count are used in the formal charge calculation. In that formula, electrons are split into two groups: unshared (lone) electrons that aren’t involved in bonds, and electrons that are shared in covalent bonds. UE stands for the unshared electrons, the lone pairs on the atom.

Formal charge is computed as the atom’s valence electrons minus the electrons assigned to it in the Lewis structure. Those assigned electrons include all unshared electrons (counted fully) plus half of the electrons involved in bonds (since bonding electrons are shared with another atom). So the commonly used expression is: FC = valence electrons − (unshared electrons + half of bonding electrons).

For example, in a molecule like water, oxygen has valence 6, it carries 4 unshared electrons (two lone pairs), and there are 4 electrons in bonds (two O–H bonds). The formal charge would be 6 − (4 + 2) = 0, showing how the unshared electrons contribute fully to the count. If there were more unshared electrons, the formal charge would become more negative; if fewer, more positive.

Choices about valence electrons or bond energy don’t match UE, and electrons shared in bonds are the bonding electrons, not the unshared ones.