Chemistry Reviews (AS level)

Chapter 8: Chapter 8

Welcome to chapter 8, which is about chapter 8. Apparently, this topic is called "Reactivity trends", but everyone knows the truth. Reactivity trends is only a small part of the topic, as it is mostly reactions. TBH Periodicity has more reactivity trends than this topic. There are mainly 3 subtopics, which they tried to squish together into one, but they aren't well connected to each other. I'll keep them in one review, but I refuse to give it the name from the textbook, as it isn't very representative at all.

Part one is about Group 2 of the periodic table. I don't know why they don't call them Alkaline Earth metals that often, but that is the name for the group. Actually, I now realise why they don't call them the alkaline earth metals, as it is quite long to write. Luckily here I can just copy and paste it, so no unnecessarily overlong phrases for me to write here. Alkaline Earth metalsAlkaline Earth metalsAlkaline Earth metals. See, that only took less than 1 sec. As long as I haven't spelt it wrong the first time, as that would then be a lot of editing. Unless I put a key at the top, as a notice of incorrectness, but that would not be very professional.

Interestingly, these elements aren't found naturally in their element, as they are very reactive. That's probably just unnecessary info though, ignore it if you wish.

This small section is mentioned a bit later on the page, but I think it belongs just here better. Reactivity increases down the group, because of increasing atomic radius and shielding so the outer electrons are more easily lost. Alkaline Earth metals have 2 outer electrons, so the jump from second to third ionisation energy is quite significant. Also as reactivity increases down the group, ionisation energies decrease.

Straight onto reactions with this one, no waiting around. Guess that's because they're so reactive lol. Not as reactive as the Alkali metals though. First up is the redox reactions. In a redox reaction, group 2 elements are oxidised, because they lose electrons (and form 2+ ions). This also means that Group 2 elements are also called reducing agents.

First is the reaction with oxygen. This is the simplest one, as it is a simple addition reaction, with a group 2 to an oxygen (as oxygen has a 2- charge), e.g. MgO. There will need to be 2 moles of alkaline earth to 1 of oxgyen, as O molecules are diatomic, and Mg is monotomic. 

Next is the reaction with water. This one's a bit different, as a hydroxide is formed, as well as hydrogen gas. This would make sense in reality though, as you could imagine that if you put an Alkaline Earth metal in water, then a gas would be released as well as an aqueous solution being made. As OH is a 1- charge, there will be 2 to a group 2. 

The last redox reaction is that of an Alkaline Earth metal and an acid (apparently specifically a dilute acid, idk). This reaction has been brought up before, in the acids and redox chapter. I mentioned it in the acids section, but it was the only acid-base reaction which wasn't displacement, and was instead redox. As mentioned though, a salt and hydrogen are made.

That's all for the reactions of pure Alkaline Earth metals, but now we have the reactions of Group 2 compounds. 

This is the second reaction with water of this mini-topic, but this time we have an Alkaline Earth metal oxide reacting with water, which forms aqueous ions of the metal and hydroxide (OH). After this, when the solution is dripping with saturation (apparently a saturated solution is one where the maximum amount of solute is dissolved), any further group 2 oxide added will mix with spare OHs and form an Alkaline Earth metal hydroxide. Also Alkaline Earth metal hydroxides aren't very soluble, but the solubility increases down the group.