Question

RESONANCE STRUCTURES how do you know which elements has positve charge or negative

Answer 1

Formal charges are used in Chemistry to determine the location of a charge in a molecule and determine how good of a Lewis structure it will be. Remember, the best resonance structure is the one with the least formal charge. This is why formal charges are very important. Atoms that are missing one or more electrons will have a positive charge. An atom with many electrons will have a negative charge. Assigningformal charges to an atom is very useful in resonance forms.

Formal charge is calculated using this format:

# of valence electrons- (#non bonding electrons + 1/2 #bonding electrons)

Curved arrow notation is used in showing the placement of electrons between atoms. The tail of the arrow begins at the electron source and the head points to where the electron will be. Make sure the arrows are clear including the single and half headed arrow. The reader must know the flow of the electrons.

There are several things that should be checked before and after drawing the resonance forms. First know where the nonbonding electrons are, keep track of formal charges on atoms, and do not break sigma bonds. Finally, after drawing the resonance form make sure all the atoms have eight electrons in the outer shell. Checking these will make drawing resonance forms easier.

When drawing a resonance structure there are three rules that need to be followed for the structures to be correct:

1. Only electrons move and the nuclei of the atoms never move.
2. Only electrons that can move are pi electrons, single unpaired electrons, and lone pair electrons.
3. The total number of electrons in the molecule do not change and neither do the number of paired and unpaired electrons.

Approaches for moving electrons are move pi electrons toward a positive charge or toward an another pi bond. Move a single nonbonding electron towards a pi bond. Move lone pair electrons toward a pi bond and when electrons can be moved in more than one direction, move them to the more electronegative atom.

Example:

Benzene is commonly seen in Organic Chemistry and it has a resonance form. Benzene has two resonance structures, showing the placements of the bonds.

Another example of resonance is ozone. Ozone is represented by two different Lewis structures. The difference between the two structures is the location of double bond.