Make your own free website on

Learn Chemistry!

Lesson 2 - Balancing Chemical Equations

Many people have seen chemical equations. Surely a large amount of people don't know what's going on, or why it's stacked up that way. You need to know how to balance an equation, and make it make sense. You can't simply write Ca + N ---> Na + C and hope it works, because it doesn't.

Section 1 - How to balance

I opted for a Quentin Tarantino approach on this lesson, as it will make it easier in the long run. Balancing is really easy, all you have to do is have the same number of each element on each side of the arrow(s). To adjust the amount neccessary, you just add coefficients. For those of you who don't remember algebra, a coeffecient is the number in front of the variable (the elements being the variable) that multiply it. This is a simple example of having equal amounts:

H + Cl ---> HCl

Makes sense, right? However, chlorine and hydrogen are both diatomic molecules, so we must add that to the chemical equation.

H2 + Cl2 ---> HCl

Now it's not right. There are two chlorines and two hydrogens on the left side, but only one of each on the right side. This is when we add a coefficient

H2 + Cl2 ---> 2HCl

Now, there are two hydrogens, and two chlorines on the left, and two hydrogens and two chlorines on the right (forming hydrogen chloride). So if I were to throw this one at you, could you do it?

Na + Cl2 ---> NaCl

This one is a little bit more tricky, but you'll soon become proficient at this. There are two chlorines on the left, but one on the right. So obviously, put a coefficient in front of the NaCl on the right, which will give you two chlorines. But wait! Now there are two Na on the right side, but only one on the left side. Simply add the coefficient of 2 to the Na to fix it.

2Na + Cl2 ---> 2NaCl

You've got the basic principle - keep it equal on both sides, and don't forget your diatomics! Lets move on to something else and then we'll come back to this.

Section 2 - Making Compounds

Now it's time to learn the very basics for forming compounds. Remember those numbers I had you write down above each column? Those will be referred to as "charges" from now on. Read lesson 1 - section 3 if you don't know what I'm talking about.

These are the basic rules for making compounds. The goal is to get the charge number to zero (hence why there are positive, and negative charges). For example (+1) + (-1) = 0. It's quite simple. All of group 1 has a +1 charge. While all of group 7 (the halogens) have a -1 charge. This means, all of group 7 can easily bond to all of group 1 with minimal amounts of headaches.

Na(+1) + Cl(-1) = NaCl(0) [Sodium + Chlorine = Sodium chloride]

Li(+1) + F(-1) = LiF(0) [Lithium + Fluorine = Lithium Fluoride]

K(+1) + I(-1) = KI(0) [Potassium + Iodine = Potassium Iodide]

H(+1) + Br(-1) = HBr [Hydrogen + Bromine = Hydrogen Bromide ]

See how easily that works? Now, when it's not as simple as 1-1, you start putting numbers into the compound. Group 2 all have +2 charges. If we bond this with group 7, which have -1 charges, we'll need 2 group 7 elements to make it 0. This is what subscripts are for. Here you can see a few examples:

Ca(+2) + Cl(-1) = CaCl2(0) [Calcium + Chlorine = Calcium Chloride]

Ba(+2) + F(-1) = BaF2(0) [Barium + Fluorine = Barium Fluoride]

And so on and so forth. If you combine elements from group 2 and group 6, the charge balances out evenly:

Ca(+2) + O(-2) = CaO(0) [Calcium + Oxygen = Calcium Oxide]

Ba(+2) + S(-2) = BaS(0) [Barium + Sulfur = Barium Sulfide]

The same works for the opposite direction:

H(+1) + O(-2) = H2O [Hydrogen + Oxygen = water]

Na(+1) + S(-2) = Na2S [Sodium + Sulfur = Sodium Sulfide]

It's the same thing when you go into groups 3 and 5, it just requires a bit more mathematical skill.

Al(+3) + O(-2) = Al2(+6) + O3(-6) = Al2O3(0) [Aluminum + Oxygen = Aluminum Oxide]

Mg(-2) + N(-3) = Mg3(+6) + N2(-6) = Mg3N2(0) [Magnesium + Nitrogen = Magnesium Nitride]

See? It's not that bad. Just get it to zero. Group 4 is slightly different. Carbon does not like to play nicely and it wont always follow these rules, so it's best to leave it out for now. However, silicon complies without problems. Group 4 can have either a +4 charge, or a -4 charge, so keep that in mind.

Si(+4) + O(-2) = SiO2 [Silicon + oxygen = silicon dioxide, which is sand]

NOTE: I left all diatomics out of the above. This was simply to show you how to make compounds, and I didn't want to confuse you by adding diatomics.

Below are 10 compound forming problems. If you feel confident, skip these and go to section 3. If not, do as many or as few as you like. The answers can be achieved through the link directly below the problems. Just write them on a separate sheet of paper, or in notepad.

1) Sodium (Na) + Oxygen (O2)

2) Hydrogen (H2) + Sulfur (S)

3) Magnesium (Mg) + Oxygen (O2)

4) Potassium (K) + Nitrogen (N2)

5) Lithium (Li) + Chlorine (Cl2)

6) Aluminum (Al) + Sulfur (S)

7) Boron (B) + Oxygen (O2)

8) Cesium (Cs) + Fluorine (F2)

9) Strontium (Sr) + Nitrogen (N2)

10) Calcium (Ca) + Bromine (Br2)


Section 3 - Combining Lesson 1 and 2

Now, you know how to form compounds, and you can balance an equation. But, can you do both? Lets review really quickly. To balance the equation, make sure there is an even amount of each element on each side of the arrow, adding coefficients as neccessary. To form a compound, get the total charge to zero, adding subscripts as neccessary. Here is a quick example

Magnesium reacting with Nitrogen

3Mg + N2 ---> Mg3N2 (magnesium nitride)

Calcium reacting with Bromine:

Ca + Br2 ---> CaBr2 (calcium bromide)

Hydrogen reacting with Nitrogen:

3H2 + N2 ---> 2NH3 (ammonia)

Hopefully you get it now, I'll give you 10 problems to try out on your own. For the answers, click the link that says answers.

1) Sodium and Chlorine

2) Beryllium and phosphorus

3) Potassium and sulfur

4) Hydrogen and Fluorine

5) Aluminum and oxygen

6) Calcium and Fluorine

7) Cesium and Nitrogen

8) Lithium and Oxygen

9) Barium and Sulfur

10) Carbon and Oxygen (same rules apply on this one)


You know how well you did. If you don't think you understand it, simply go back and re-read it. No need to get frustrated, chemistry doesn't come easy to all of us. If you think you've grasped this concept quite well, then continue on. The next thing we'll talk about is the poly atomic ions, since not all compounds are binary (two parts, two elements in this case).