[Music] hi and welcome back to freci lessons. co.uk by the end of this video you should be able to describe how metal ions are positive and most non-metal ions are negative you should then be able to relay charges on ions to groups in the periodic table this might seem like a slightly weird topic but in the next video we're going to use this to develop a really useful skill in chemistry which is working out the formula of ionic compounds let's start with a quick recap of ionic compounds here's a periodic table and remember that we find metals on the left and non-metals on the right we've seen that ionic compounds are formed when metals react with non-metals ions are atoms with a charge and remember that Metals form positive ions and most non-metals form negative ions I'm showing you some metal ions here we've got na+ mg2+ and al3+ the first idea that you need to understand is that the charge on a metal ion is often the same as the group number in the periodic table so sodium is in group one and forms a 1 plus ion magnesium is in group two and forms a 2+ ion and aluminium is in group three and that forms a 3 plus ion we can also see this with other metals from these groups which I'm showing you here both lithium and potassium are in group one and they form one plus ions brillium and calcium are both in group two and they form two plus ions and gallium and indium are in group three and these can form three plus ions now I should point out that certain Metals do not follow this pattern and a good example are the transition metals these can form several different ions a good example of this is Ion this can form a two plus ion and a three plus ion scientists call these Ion 2 and ion 3 and you'll sometimes see these in compounds another good example is copper which can form a one plus ion and a two plus ion and again we call these copper 1 and copper two let's take a look now at non-metal ions and I'm showing you two non-metal ions here we've got the oxide ion O2 minus and the fluide ion F minus now just like with metal ions we can relate these to their groups in the periodic table Oxygen's in group six and forms a 2 minus ion so does sulfur which is also in group six this forms the sulfide ion S2 minus flines in group s and this forms the one minus fluide ion chlorine and bromine are also in group seven and they also form one minus ions now there are some non-metal ions which consist of several non-metal atoms chemically combined and we can see some of these here I should point out that if an exam question requires you to use one of these ions then you will be given the formula now there are a couple of non-metal ions which are different to the rest and that's because they're positive unlike the rest of the non-metal ions which are negative these ions are the hydrogen ion H+ and the ammonium ion nh4 plus again you could see these in exam questions I'm showing you here the ionic compound sodium sulfate which has the formula na2so4 and calcium hydroxide which has the formula coh2 in the next video you're going to learn how to work out the formulas of compounds such as these it's a really useful skill to learn and will help you a lot in chemistry okay so hopefully now you should be able to describe how metal ions are positive and most non-metal ions are negative you should then be able to to relay charges on ions to groups in the periodic table [Music]