Key Words

Reactivity, metals, periodicity, corrosion, sacrificial metals, galvanising, ores, electrolysis, thermal decomposition, carbon, hydrogen

Explanation

I like to think of this in terms of people and as a result make this much bigger and easier to picture, I always find, especially with younger years, that concepts of particles and atoms is a little too abstract for them to apply it so by modelling it with things we know it makes life easier.

So lets just imagine you have started a relationship with someone, whether that be at school, down your street or at a club, this person is person A. Now you think you're really happy with person A, but all of a sudden in to the same group comes person B.

Here's the problem you now face, person B is incredibly attractive, they're good looking, funny, smart and you get on like a house on fire, great. You then need to make a decision, do you stick with person A or do you go with (the better) person B. 

Now for you this may be a conundrum, do you sacrifice happiness for loyalty, a difficult decision that plagues everyone in any form of relationship, and that's because you have a thing called ethics, metal do not, they will just get with person B and forget person A ever existed. 

Now lets apply this model to some chemical equations, lets say you are a sulfate ion and you are bonded to a copper ion (person A), therefore you are called copper sulfate. I then add magnesium, a more reactive (and therefore attractive) metal, you then bond with the magnesium leaving the copper on its own and get the following equation:

copper sulfate + magnesium -> copper + magnesium sulfate

Do you see how all we've done is switch the copper and magnesium around? 

Now just to be thorough lets do this with the chemical equation:

CuSO4 + Mg -> Cu + MgSO4

Again, can you see the swap?

This is all because magnesium is more reactive and higher on the reactivity series, which is as follows:

Potassium
Sodium
Calcium
Magnesium
Aluminum
Carbon
Zinc
Iron
Tin
Lead
Copper

Hydrogen
Silver
Gold
Platinum

So therefore in a displacement reaction like that seen above, if the metal is more reactive than the metal in the sulfate (or carbonate, or hydroxide etc.) then it will displace the other, try some in the comments and I'll let you know if they are correct!

You will also notice that in the series I have added carbon and hydrogen, surely that's not right, they're not metals... Well there is a good reason, these two non-metals allow us to compare the reactivity and also tell us how we get these metals. 

So as anyone that has ever played a game like minecraft will know metals come from things called ores. An ore is a rock that contains enough metal that when it is extracted is done so for a profit. So if I have an ore of aluminium that is more reactive than carbon I am going to have to use a process called electrolysis to remove it from it's ore, this uses a lot of energy and is a (relatively) recently developed process but necessary as due to being highly reactive they form incredibly strong bonds with their ores.

Metals such as copper and iron that are found between hydrogen and carbon are easier to extract, heat energy is really enough to break these bonds and collect the ores, this needs to be done in the presence of carbon however so the metal oxide is also broken down:

Without carbon:

CuCO3 -> CuO + CO2

but with carbon 

2CuCO3 + C -> 2Cu + 3CO2

And voila we have our metal.

But what about those less reactive than hydrogen, well, these are so unreactive they are often found on their own, often in streams and rivers.

Exams

Most people struggle remember the order, this is where you will most likely lose marks, trying to figure out if a metal will react with a salt or not or perhaps how to extract the metal from it's ore, you must learn this order, it may be given to you but don't count on it. 

Secondly be careful with the equations, word equations and chemical equations are different, if the question asks for a word equation give a word equation, if chemical you must give a chemical equation, but check it's balanced.

Mistakes

As above, read the question, there are few pitfalls here but the difference between word and chemical equations is a common mistake to make.

Tricks

Find or make up a mneumonic for the series, I have never remembered one personally but a few minutes searching online found this one:

Please Send Little Charlie McLean A Zebra If The  Lean Horse Can't  Munch Sweet Green Peas

When making one up remember; the ruder the better, you're more likely to remember if it's a little naughty

Extension

So this may be brought up when answering questions about group 1 and 2, you will notice the most reactive metals here are in these two groups, there are good reasons for this when you read the chapter on these groups but I will not cover it now. 

Also a question that could come up but never has, why was the bronze age before the iron age, tricky right? wrong. It's very simple, iron is more reactive than copper so forms stronger bonds in it's ore, it's therefore harder to separate, only when we were able to produce enough heat energy to break these bonds was iron able to be extracted.

Lastly jewelry, we use gold, silver and platinum in jewelry because it is unreactive, it will not react with the oxygen in the air and therefore does not tarnish easily.