![]() CIE use this modern system, but it has a disadvantage when using the Periodic Table to work out charges on ions. Modern numbering includes the transition metals, and the numbers go from 1 to 18. Helium, of course, only has room in its outer level for 2 electrons. Note: The last Group in the Periodic Table (the Noble Gases) is usually called Group 0, but was sometimes called Group 8. This has the big advantage for students at this level that it counts the number of electrons in the outer energy level of the atoms of each element. The numbers at the top of the Groups (the vertical columns in the table) are the old group numbers - from 1 to 7 and then 0. Let's look again at the Periodic Table from earlier on. Where you can work out the number of charges on a metal ion from a Periodic Table In lead(II) bromide, the lead ion has 2+ charges. In iron(III) fluoride, the iron ion has 3+ charges. ![]() ![]() In copper(II) oxide, the copper ion has 2+ charges. We are talking about the charges on a metal ion, and so they will always be positive. This tells you how many positive charges the ion has. Quite a lot of compound names have a Roman numeral as a part of the name.This is known as the oxidation state or oxidation number of the element. Where the name of the compound tells you the number of charges on a metal ion How do you know how many charges a positive ion has? We will have more to say about this below. These contain the non-metal plus other things as well - often oxygen. Note: Are there non-simple ions? Yes! "Complex ions" are also common in the non-metals. Phosphorus does form a phosphide ion, but it isn't common. The ones mentioned above are the only simple ions you are likely to come across. Not all of the non-metals form simple ions. So the ions are called nitride, oxide, sulfide, fluoride, chloride, bromide, and iodide. Simple ions from non-metals have their endings changed to " ide". This isn't something you need to worry about at the moment. Some of the elements just to the left of the green bit tend to have properties which are a mixture of metal and non-metal. Note: The dividing line between metals and non-metals isn't quite as clear-cut as this. You can see that the non-metals are all found on the right-hand side of the Periodic Table. Here is a simplified version of the Table missing out the bits that aren't relevant at the moment. There is a simple pattern from the Periodic Table. ![]() How do you know if something is a metal or non-metal? Simple non-metal ions (containing only one type of atom) that you will meet are negative. Two other positive ions you will meet are H + and NH 4 +. How do you know if an ion is positive or negative? It is an acid in solution (which will contain H + ions), There have to be equal numbers of positive and negative charges in the compound. Secondly, all these ionic compounds are overall electrically neutral. How writing formulae for ionic compounds worksįirst of all, of course, you need to know that the compound is ionic. Working out formulae for ionic compounds is something that you should have met and been comfortable with in whatever course you did between the ages of 14 and 16, and you may feel happy to skip through most of this section. This statement deals with writing formulae for ionic compounds.īefore you go on, you should find and read the statement in your copy of the syllabus. Chemguide: CIE A level chemistry support: Learning outcome 2.3.1Ĭhemguide: Support for CIE A level Chemistry
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