Formal Charge.

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Presentation transcript:

Formal Charge

Formal Charge It is a way to predict what structure is most likely. # of valence e- in atom minus # of e- assigned to it in the molecule

Formal Charge Lone pairs count individually Bond pairs count as half =(# of val e- in atom) - ((# of e- in lone pair) +1/2(# of e- in bond pairs))

Formal Charge Ex: Which one is the most plausible structure? :S=C=S: or :C=S=S: Val e 6 4 6 4 6 6 e pic 6 4 6 6 4 6 FC 0 0 0 -2 +2 0 .. .. .. ..

Formal Charge Plausible? Usually the one with no formal charge. If required, they should be the smallest possible charges, and negative should appear on the most electronegative element. Adjacent atoms should not carry a formal charge of the same sign. Total formal charge must be zero for a neutral molecule and equal to the charge of an ion. So……?

Formal Charge Ex: Which one is the most plausible structure? ::S=C=S:: or ::C=S=S:: Val e 6 4 6 4 6 6 E’ 6 4 6 6 4 6 FC 0 0 0 -2 +2 0

F P O O P F Val e e pic FC

Lewis structures, shapes, angles, hybridization BONDING Lewis structures, shapes, angles, hybridization

LEWIS STRUCTURES COVALENT compounds Elements share electrons A line represents TWO shared electrons OCTET rule Every element wants at least 8 electrons (EXCEPT hydrogen and helium ~ they only want 2) Other exceptions ~ Be only wants 4, B only wants 6 Some can have an EXPANDED octet (only 3rd energy level and below since the extra electrons go in d orbitals)

STEPS FOR LEWIS STRUCTURES Draw the atoms The central atom goes in the middle, and the others go around it The central atom is usually the one you have the LEAST of (or the least ELECTRONEGATIVE if you only have one of two or more elements) Count your total number of valence electrons Use your periodic table to add up the number of valence electrons in the formula

STEPS FOR LEWIS STRUCTURES BOND Everything must be bonded to the central atom Fix OUTER atoms Every outer atom must have 8 electrons (or 2 if it is hydrogen) Fix CENTRAL atom Extras = LONE PAIR(S) If your count is ZERO and the central atom still does not have 8, then you need a MULTIPLE BOND

A COUPLE EXAMPLES CH4 NF3

A COUPLE EXAMPLES CO2 SiO32-