 When I go traveling I like to look at big metal structures because oftentimes some of the most impressive structures are big structures made out of metal. It's fun to have a look at the where they're reacting and how they're reacting. So here's the Sydney Harbour Bridge and here is a nice big spot of oxidation here so there's rust forming. This is the Golden Gate Bridge here in San Francisco and again you can see where the paint is flicking away from the orange bar here. This is just one above one of the supporting legs, the legs were built in this concrete area here where they sucked out the water from. This is the Eiffel Tower in Paris and again we can see where the paint is flicked away, we can see some oxidation of the metal underneath it. Now all three of these structures are made of iron. In these two cases it's steel, in this case it's iron, wrought iron, pig iron which is a bit more brittle than the steel that was used for the Sydney Harbour Bridge and the Golden Gate Bridge. Down here this is the back of the Statue of Liberty, it doesn't really look like it, it is, it's an angle you don't normally see. Again the copper has oxidized, it was brown when it was first built but exposure to the oxygen in the air and sea air with salt and water you get an oxidation happening together, the vertigree, the pretty green colour of the copper. All of these are down to the reactivity of the metals and them reacting with their environment so let's have a look at some of the reactions of metals. So let's have a look at some of the reactions of metals with water for example. So down here I have a lump of sodium that's going into a solution of water and phenolphthalein which is an indicator and thanks to Reese Lewis for the videos and in fact all the videos in this video. As it's reacting you get a hydroxide iron being produced from the metal and when it's reacting with the water and also some hydrogen gas and that's what the bubbles are that are forming. Hydrogen gas is quite volatile so if there's enough heat energy you should catch on fire and as it catches on fire we can get explosions happening sometimes. So that's an example of a metal reacting with water so you probably wouldn't make a bridge out of sodium for many reasons but one reason is that the sea air wouldn't be very good for it would explode pretty much straight away. So let's have a look at the reactions here. So sodium metal is reacting with water now we're making a hydroxide now I'm just going to be sodium hydroxide and also making hydrogen gas so now we need to make this balance we've got too many hydrogens over here we've got two hydrogens three hydrogens but only two on this side so we need to make four hydrogens in total so if we doubled that now we've got two hydrogens but now we need two sodiums as well and we're going to need two waters so we've got four hydrogens one two three four hydrogens two sodiums two sodiums two oxygens two oxygens so now we're balanced so in this reaction now we're acting a very reactive metal sodium with water and we get our hydroxide being produced and hydrogen gas now sodium is a very reactive metal so it will do this but less reactive metals won't so if you put gold in water you won't see gold hydroxide forming you won't see any bubbles of hydrogen because gold is very unreactive so the reactivity of the metal determines whether this will happen or not and also how fast it will happen