As of 07/12/05 there are 1056 structures in the database. A Best Lewis Structure and Donor Acceptor Interactions Tutorial is available to help you interpret those output sections. These Lewis structure calculations are done using NBO Analysis. Answer some Study Questions to help your understanding of some interesting chemistry. Wolfram Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels. Starting structure. Methane; Benzene; Water dimer; Optimize; Atoms. Turn off atom manipulation Off; Hydrogen H; Lithium Li; Beryllium Be; Carbon C; Nitrogen N; Oxygen O; Fluorine F; Sodium Na; Magnesium Mg; Aluminium Al; Silicon Si; Phosphorus P; Sulfur S; Chlorine Cl; Bromine Br; Iodine I; Increase charge of selected atom +1; Decrease charge.
Sometimes it's difficult to tell which of two possible Lewis structures of a compound represents the actual bonding of the molecule. In those cases we resort to calculating what's called the formal charge of each atom. Formal charge is just a way of bookkeeping that helps us to decide which of multiple Lewis structures is the likely true bonding arrangement of a covalent molecule. The sum of the formal charges, with a couple of extra rules, will help us to decide which of multiple-possible valid Lewis structures is likely to be the correct one. Here's how it's done.
Calculating formal charge
For each atom
- Count the number of valence electrons of the neutral atom.
- Subtract the number of non-bonding electrons (usually in lone pairs).
- Subtract the number of bonds shared by the atom.
Example: CH4 (methane)
The carbon in CH4 has four electrons as a neutral atom. It has no lone pairs, and it shares four bonds, so the formal charge is zero. Each hydrogen atom has one electron as a neutral atom, no lone pairs and shares one bond, for a formal charge of zero. All atoms in the molecule have zero formal charge, the 'happiest' situation for any molecule.
Example: H3C(CO)CH3, (acetone)
Lewis Dot Structure
The central carbon has a formal charge of 4 (valence electrons) - 0 (lone pairs) - 4 (bonds) = 0. The oxygen has a formal charge of 6 - 4 - 2 = 0 (same ordering of terms). Each of the methyl (CH3) carbons has a formal charge of 4 - 0 - 4 = 0