A bond is the sharing of 2 electrons. Covalent bonds share electrons in order to form a stable octet around each atom in the molecules. Hydrogen is the exception it only requires 2 electrons (a duet) to be stable. How do we draw a covalent Lewis Dot Structure? Level 1 (basic) 1. Add up all the valance electrons of the atoms involved. ex CF4 So C has 4 and F has 7 (x4 we have 4Fs) = 32 valence electrons 2. You need to pick the central atom. This is usually easy, this atom will be surrounded by the others. Never H. So C will be surrounded by F's. 3. Now we create our skeleton structure by placing bonds in. A bond is a dash that represents 2 electrons. We have now placed 8 electrons as 4 bonds. We have 32-8= 24 more to place. 4. Starting with the outer atoms add the remaining electrons in pairs until all the electrons have run out.
All 32 electrons are now in place, count the dots around each F. 6 dots and a bond (2 electrons) is 8. We have our octet. The carbon has 4 bonds (2electrons) for its 8. DONE Level 2 (Double and Triple bonds) Same rules apply until #4 1. Add up all the valance electrons of the atoms involved. ex CO2 So C has 4 and O has 6 (x2 ) = 16 valence electrons 2. You need to pick the central atom. This is usually easy, this atom will be surrounded by the others. Never H. So C will be surrounded by O's. 3. Now we create our skeleton structure by placing bonds in. A bond is a dash that represents 2 electrons. We have now placed 4 electrons as 2 bonds. We have 16-4=12 more to place. 4. Starting with the outer atoms add the remaining electrons in pairs until all the electrons have run out.
All 16 electrons are now in place, count the dots around each O. 6 dots and a bond (2 electrons) is 8. We have our octet. The carbon has 2 bonds (2electrons) for its 4..? We need 8, so move a pair of electrons from the O to between the C and O. It will share 2 pairs of electrons instead of 1. It now has a double bond instead of a single bond.
now they all have an octet, it cleans up like this Make it symmetrical. Level 3-Lewis Dots of Polyatomic Ions Same rules apply, at the end they get brackets and a charge AP Chemistry and or College Level Rules 1. Determine whether the compound is covalent or ionic. If covalent, treat the entire molecule. If ionic, treat each ion separately. Compounds of low electronegativity metals with high electronegativity nonmetals (DEN > 1.7) are ionic as are compounds of metals with polyatomic anions. For a monoatomic ion, the electronic configuration of the ion represents the correct Lewis structure. For compounds containing complex ions, you must learn to recognize the formulas of cations and anions. 2. Determine the total number of valence electrons available to the molecule or ion by:
3. Organize the atoms so there is a central atom (usually the least electronegative) surrounded by ligand (outer) atoms. Hydrogen is never the central atom. 4. Determine a provisional electron distribution by arranging the electron pairs (E.P.) in the following manner until all available pairs have been distributed:
5. Calculate the formal charge (F) on the central atom.
6. If the central atom formal charge is zero or is equal to the charge on the species, the provisional electron distribution from (4) is correct. Calculate the formal charge of the ligand atoms to complete the Lewis structure. 7. If the structure is not correct, calculate the formal charge on each of the ligand atoms. Then to obtain the correct structure, form a multiple bond by sharing an electron pair from the ligand atom that has the most negative formal charge.
8. Recalculate the formal charge of each atom to complete the Lewis structure. on to Formal Charge Chemical Demonstration Videos |
Free Lewis Dot Structure Calculator
Every chemistry student has to learn how to draw Lewis Dot Structures. The key is to understand the steps and practice. Lewis Structures are important to learn because they help us predict: the shape of a molecule. How the molecule might react with other molecules. The physical properties of the molecule (like boiling point, surface tension, etc.). Drawing Lewis Structures. Most resonance structures and coordination compounds are also supported. Simply follow the steps below: If you do not already know the name or chemical formula of the molecule you wish to generate a dot structure for, you can browse the list of molecules at molcalc.org by clicking here.