making compounds from atoms Or making stuff from other stuff CHEMICAL REACTIONS making compounds from atoms Or making stuff from other stuff

The Law of Conservation of Matter This law states that Matter cannot be created or destroyed, therefore During a chemical reaction you must end with the same amount of stuff that you started with

What’s Happening? During a chemical reaction, electrons from one atom are either a) being shared with another atom or b) being donated to another atom In either case this causes the two atoms to bond together to form a compound A compound is when two or more atoms bond together

The resulting compound has completely different properties than either of the beginning products Na (sodium) is a metal. It reacts violently with water and explodes. Cl (chlorine) is a deadly poisonous gas. When they react with each other, the product is NaCl (sodium chloride) which is simply table salt.

Watch reaction

2 Types of Reaction Covalent bond This is when electrons are shared between atoms This type of bond forms between two non-metals Examples: H2O, CO2

Ionic bond This is when electrons from one atom are donated to the other This forms two ions. (What’s an ion?) One is positive and one is negative The two ions are attracted to each other because of their opposite charges This type of bond forms between a metal and a non-metal Examples: CaCl2, KI, NaCl

Let’s try an easy one To make water you need… Correct, hydrogen and oxygen Now, in reality both of these gases exist in diatomic form so they look like this H2 and O2 or

this

So if these two gases are to react, the diatomic form will be involved To represent this reaction we write the molecular formulas in an equation like this H2 + O2  The arrow is kind of like an equals sign in math except that you would read it like, “H2 plus O2 yields…” Get it? What does hydrogen and oxygen make again? Oh that’s right, water

What’s the chemical formula for water? Oh yeah H2O……soooooo…. H2 + O2  H2O (H2 + O2 yields H2O) But wait…something’s wrong! What did that law say? That’s right!

H2 + O2  H2O How many hydrogens are on the left? Correct, there are 2 How many are on the right? So we’re obeying the law so far What about the oxygens? There are___on the left and___on the right…. uh oh. Now what?

Now We Have to Balance It!! Balancing equations is just a way for us to try to figure out what is happening We manipulate the numbers until it makes sense based on the Law of Conservation of Energy As we stated it, H2 + O2  H2O, implies that 1 diatomic hydrogen molecule reacts with 1 diatomic oxygen molecule to make 1 water molecule But mathematically, this can’t be because we lost an oxygen and that’s against the law

Luckily this is on paper or the computer so.. …we can change stuff around until it makes sense This is called balancing the equation To balance you place coefficients in front of the chemical symbols until the reaction obeys the law Let’s get back to our equation

___H2 + ___O2  ___H2O So, the problem was the oxygen. Let’s start there. What coefficient, placed in front of the H2O will make it obey the law? Correct, a 2 ___H2 + ___O2  2H2O Alright, so 2 oxygens on the left and 2 x 1 oxygens on the right, that makes 2. Everything’s good. No wait a minute… Uh oh…Now how many hydrogens are on the right? What’s 2 x 2? Correct, there are 4 How many hydrogens are on the left? What do we do?

CORRECT! We put another coefficient in front of the H2 to balance that. 2H2 + ___O2  2H2O Now is it right? Check the numbers. How many on the left and how many on the right? See? Now its balanced, so we can say that 2 diatomic hydrogen molecules react with 1 diatomic oxygen to form 2 water molecules. Or, 2 H2’s plus 1 O2 yields 2 H2O’s

So what does all this look like? What’s really going on? 2H2 O2 2H2O