Complex Lewis Structures

[Doreen Liu 4D]

Can someone explain what the process is when trying to draw a complex Lewis Structure? For example, the lewis structure for section 2B question 11 part c - glycine.

[MMckinney_4H]

For Formaldehyde, first note that they give you HCHO as opposed to H2CO or something of that nature. This is because you are supposed to use this as a guide to how to draw the structure. Carbon is supposed to be connected to both of the Hydrogen atoms. From here, you calculate the number of valence electrons in the structure to be 12 (Each hydrogen has 1, Carbon has 4, Oxygen has 6). You want to leave the hydrogens alone when assigning electrons since they only have one valence to offer, they should only have one bond. So you attach two free electrons to the carbon and four to the oxygen. After drawing this, you check the formal charge and discover that carbon has a charge of -1 and oxygen has a formal charge of +1. You can't give oxygen both of the free electrons or else the formal charge will still be messed up. So, you double bond carbon to oxygen with carbon's two former free electrons. This gives all of the atoms a formal charge of 0, so this is the best structure.