The formal charge of an atom in a Lewis formula is the hypothetical charge you obtain by assuming that bonding electrons are equally shared between bonded atoms and that the electrons of each lone pair belong completely to one atom. When several Lewis Structures can be written for a given compound, those which contain the smallest formal charges are preferred. When two proposed Lewis formulas for a molecule have the same magnitudes of formal charges, choose the one with the negative formal charge on the more electronegative atom. It should also be noted that a structure for H 2 SO 4 can be written that has zero formal charges. This is accomplished by putting double bonds between the S and O atoms which do not have H's attached to them.
Bond length is the distance between the nuclei in a bond.
These are determined by X-ray diffraction. This is always an average distance, because atoms are always vibrating with respect to each other, so there is really no fixed distance between any two nuclei. Bond length decreases from single to double to triple bonds. Bond energy is the average enthalpy change for the breaking of an A-B bond in a molecule in the gas phase. You can use a table of B.E's. to estimate heats of reaction.