Formal Charge When more than one resonance structure is possible, the determination of the best structure can made based on the formal charges in the structure. The calculation of the formal charge is given by: Formal Charge = # valence electrons - % bonding electrons - lone pair electrons We determined that the structure of BFs is an exception to the octet rule (see above). 4. a) Determine the formal charge on B and F in this structure. Valence e on B Valence e on F -½ bonding e- lone pair e= bonding e- lone pair e= We could draw a different resonance structure by moving a lone pair of electrons off one of the F atoms and make a second bond to the B atom (see figure on next page): Student Name: Date b) The octet rule is obeyed, but this is not the structure of BF3. To see why it is not, determine the formal charges of B and F in this second structure. Valence e on B 3-% 8 bonding e- 0 lone pair e= Valence e on F-% 1 bonding e- 2 lone pair e= The formal charges are non-zero and there is a positive charge on the most electronegative element, F. The best resonance structures have the smallest possible formal charges, and negative charges on electronegative elements.
Formal Charges
Formal charges have an important role in organic chemistry since this concept helps us to know whether an atom in a molecule is neutral/bears a positive or negative charge. Even if some molecules are neutral, the atoms within that molecule need not be neutral atoms.
Polarity Of Water
In simple chemical terms, polarity refers to the separation of charges in a chemical species leading into formation of two polar ends which are positively charged end and negatively charged end. Polarity in any molecule occurs due to the differences in the electronegativities of the bonded atoms. Water, as we all know has two hydrogen atoms bonded to an oxygen atom. As oxygen is more electronegative than hydrogen thus, there exists polarity in the bonds which is why water is known as a polar solvent.
Valence Bond Theory Vbt
Valence bond theory (VBT) in simple terms explains how individual atomic orbitals with an unpaired electron each, come close to each other and overlap to form a molecular orbital giving a covalent bond. It gives a quantum mechanical approach to the formation of covalent bonds with the help of wavefunctions using attractive and repulsive energies when two atoms are brought from infinity to their internuclear distance.
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