Formal charge: kind of confused?
why cant i get -1?
tinypic
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ok in class we did this.
and for O FC= 6-4-3=+1
but S FC = -1 (I get 6-4-1= +1) which is wrong. what am i doing wrong?
i solve by doing: group # - total (bonds and lone pairs(each = 1)) - lone pairs (each pair = 1)
Formal charge is a concept used to determine the distribution of electron density in a molecule or polyatomic ion. It helps us understand the relative stability and reactivity of different atoms within a structure.
To calculate the formal charge (FC) of an atom, you should follow the equation: Formal Charge = Group Number - Total Valence Electrons.
Let's analyze the example you provided. You are trying to calculate the formal charge of an oxygen atom (O) and a sulfur atom (S).
For oxygen (O):
1. Determine the group number of oxygen. Since oxygen is in Group 6 of the periodic table, its group number is 6.
2. Calculate the total number of valence electrons for oxygen. In this case, we have 4 valence electrons since oxygen is in Group 6.
3. Subtract the total number of valence electrons from the group number: FC = 6 - 4 = +2.
For sulfur (S):
1. Determine the group number of sulfur. Since sulfur is in Group 6 of the periodic table, its group number is also 6.
2. Calculate the total number of valence electrons for sulfur. Since sulfur is in Group 6, it has 6 valence electrons.
3. Subtract the total number of valence electrons from the group number: FC = 6 - 6 = 0.
Based on the calculations above, the formal charges of oxygen and sulfur are +2 and 0, respectively.
Now, let's address the discrepancy you mentioned in your classwork. It seems that you tried to calculate the formal charge of sulfur (S) as -1 instead of 0. The error in your calculation might be that you subtracted the number of lone pairs (each pair = 1) twice. The correct approach is to consider each lone pair as one entity, not as individual electrons. So, you should only subtract the lone pairs once from the total valence electrons.
To summarize, when calculating the formal charge of an atom, remember to:
1. Determine the group number of the atom.
2. Calculate the total number of valence electrons for the atom.
3. Subtract the total number of valence electrons from the group number to obtain the formal charge.
By following these steps, you will be able to correctly determine the formal charge of an atom within a molecule or ion.