How do you determine formal charge in a molecule?

Formal charge in a molecule is determined by subtracting the number of non-bonding electrons and half the number of bonding electrons from the total number of valence electrons.

To understand this in more detail, let's break down the process. The formal charge of an atom in a molecule is a hypothetical charge the atom would have if all atoms in the molecule shared their electrons equally. It is calculated using the formula: Formal charge = Valence electrons - Non-bonding electrons - 1/2 Bonding electrons.

Valence electrons are the electrons in the outermost shell of an atom that are involved in chemical reactions. Non-bonding electrons, also known as lone pairs, are electrons that are not involved in bonding. Bonding electrons are the electrons involved in forming bonds between atoms.

To calculate the formal charge, you first need to know the number of valence electrons for the atom in question. This can be found on the periodic table. For example, carbon, which is in group 14, has 4 valence electrons.

Next, count the number of non-bonding electrons. These are the electrons that are not involved in a bond, and are usually represented as dots in Lewis structures.

Finally, count the number of bonding electrons. These are the electrons that are involved in bonds with other atoms. In a single bond, there are two bonding electrons, in a double bond there are four, and in a triple bond there are six. However, since these electrons are shared between two atoms, you only count half of them for each atom.

Subtract the number of non-bonding electrons and half the number of bonding electrons from the total number of valence electrons to get the formal charge.

Remember, the sum of the formal charges of all atoms in a molecule or ion must equal the overall charge of the molecule or ion. This is a useful check to ensure your calculations are correct. Understanding formal charge is crucial for predicting the structure and reactivity of molecules, and is a fundamental concept in chemistry.