Use the reference charts given. Remember that you can only use previously defined atoms when defining your current atom. This is done by using neighboring atoms to the atom you are describing. Again, the reference charts are helpful in locating bond lengths and angles. The bond length of each kind of bond varies very little from one particular compound to another.
Angles can be positive and negative to represent directions.
If one atom is going into the screen and another is coming out of the screen, one angle should be defined as negative and the other as positive. It does not matter which you chose to be positive or negative. The Shodor Education Foundation, Inc.