Lewis Structures Worksheet Guidelines If you are able to construct the Lewis structure for a covalent compound, you will be able to see how the electrons are involved in the bonding. There are several ways to determine the Lewis structure of a compound. Here is one step-­‐by-­‐step approach: Guidelines for Construc0ng LEWIS STRUCTURES: For Covalent Compounds 1. Determine the number of each kind of atom from the molecular formula. 2. Determine the total number of valence electrons available by counFng the number of valence electrons for each atom in the compound and then adding the numbers of electrons from the individual atoms together. Special note for polyatomic ions: •  Add one electron for each nega0ve charge. •  Subtract one electron for each posi0ve charge. 3. Determine the number of valence electrons needed to saFsfy the octet rule for all atoms EXCEPT hydrogen, H. The maximum number of valence electrons required for hydrogen is two. •  The maximum number of valence electrons required to saFsfy the octet rule for all other atoms is eight. 4. Determine the number of electrons involved in bonding by subtrac0ng the number of available electrons from the number of needed electrons. 5. Determine the number of bonds by dividing the number of bonding e-­‐s by two because there are two electrons in a single bond. 6. Place the chemical symbol of the element present in the smallest amount in the center of the molecule and arrange all other atoms around it using the number of bonds calculated in Number 5 above. Represent each bond by a single line between the bonded atoms. Then add the nonbonding electrons so that every atom (EXCEPT H) has access to eight electrons. Hydrogen should have access to two electrons. Special note for polyatomic ions: Place square brackets around the [structure] and put the charge outside the brackets in the upper right-­‐hand corner. Chemistry 101 Lewis Structures Worksheet Silicon tetrachloride: SiCl4 Atoms Present Si Cl Cl Cl Cl Total e-­‐ Available Electrons 4 7 7 7 7 32 Needed electrons 8 8 8 8 8 40 Bonding electrons 40e-­‐ -­‐ 32e-­‐ = 8e-­‐ # of Bonds 8e-­‐ / 2e-­‐ per bond = 4 bonds Phosphate ion: PO4-­‐3 3-­‐ Extra Atoms Present P O O O O e-­‐ Total e-­‐ Available Electrons 5 6 6 6 6 3 32 Needed electrons 8 8 8 8 8 Bonding electrons 40e-­‐ -­‐ 32e-­‐ = 8e-­‐ # of Bonds 8e-­‐ / 2e-­‐ per bond = 4 bonds 40 Nitrogen triiodide: NI3 Extra Atoms Present Available Electrons Needed electrons Bonding electrons # of Bonds Total e-­‐ Hydrogen sulfide: H2S Extra Atoms Present Available Electrons Needed electrons Bonding electrons # of Bonds Total e-­‐ Carbon dioxide: CO2 Extra Atoms Present Available Electrons Needed electrons Bonding electrons # of Bonds Total e-­‐ Acetylene: C2H2 Extra Atoms Present Available Electrons Needed electrons Bonding electrons # of Bonds Total e-­‐ Sulfur dioxide: SO2 Extra Atoms Present Available Electrons Needed electrons Bonding electrons # of Bonds Total e-­‐ Carbonate ion: CO3-­‐2 Extra Atoms Present Available Electrons Needed electrons Bonding electrons # of Bonds Note: Total e-­‐