Chemistry Spl

Need to figure out if an atom is negative, positive, or neutral? Here's the formula for figuring out the formal charge of an atom:
Formal charge = [# of valence electrons] [electrons in lone pairs + 1/2 the number of bonding electrons]
This formula explicitly spells out the relationship between the number of bonding electrons and their relationship to how many are formally owned by the atom. However, since the number of bonding electrons divided by 2 terms is also equal to the number of bonds surrounding the atom, here's the shortcut formula:
Formal Charge = [# of valence electrons on atom] [non-bonded electrons + number of bonds].
Let us apply it to some examples. for example BH4 (top left corner).
The number of valence electrons for boron is 3.
The number of non-bonded electrons is zero.
The number of bonds around boron is 4.
So formal charge = 3 (0 + 4) = 3 4 = 1
The formal charge of B in BH4 is negative 1.
Lets apply it to :CH3 (one to the right from BH4)
The number of valence electrons for carbon is 4
The number of non-bonded electrons is two (it has a lone pair)
The number of bonds around carbon is 3.
So formal charge = 4 (2 +3) = 4 5 = 1
The formal charge of C in :CH3 is negative 1.
Same formal charge as BH4!
Lets do one last example. Lets do CH3 (with no lone pairs on carbon). Its the orange one on the bottom row.
The number of valence electrons for carbon is 4
The number of non-bonded electrons is zero
The number of bonds around carbon is 3.
So formal charge = 4 (0 +3) = 4 3 = +1
You can apply this formula to any atom you care to name.

Balancing chemical equations isn't difficult, once you know the way to do it. Start by finding out how many atoms of each type are on each side of the equation. Some teachers recommend making a little table listing the numbers of each atom for the left hand side and for the right hand side.
Next, look for an element which is in only one chemical on the left and in only one on the right of the equation. (But it is usually a good idea to leave hydrogen and oxygen until you've done the others first).
To balance that element, multiply the chemical species on the side which doesn't have enough atoms of that type by the number required to bring it up to the same as the other side. The number is called the coefficient.
BUT
If you have to multiply by, say, 2 1/2, do so, THEN multiply EVERYTHING on each side of the equation by two to get rid of the half.
We don't like having halves in equations, as you can't get half a molecule.
Now look for the next element or species that is not balanced and do the same thing.
Repeat until you are forced to balance the hydrogen and oxygens.
If there is a complex ion, sometimes called a polyatomic ion, on each side of the equation that has remained intact, then that can often be balanced first, as it is acts as a single species. The ions NO3- and CO32- are examples of a complex ion.
A VERY useful rule is to leave balancing oxygen and hydrogen to the last steps as these elements are often in more than one chemical on each side, and it is not always easy to know where to start. Some people also say you should leave any atom or species with a valency of one one until the end, and also generally leave anything present as an element to the end.
In Example 1 above, you would balance the carbons first, by putting a 3 in front of the CO2, then balance the hydrogens by putting a 4 in front of H2O and finally the oxygens (which are in more than one compound on the right, so we leave them until last) by putting a 5 in front of the O2.