Bear with me on this article as it is my first and my thought pattern does jump around a lot when I am trying to explain stuff i.e. you may be confused with the way I explain stuff. And yes I know this is long.

The most useful tool that any chemist, in fact any scientist, can utilise is the periodic table of elements. A list of 118 elements (four of which are not verified) that everything that exists is made out of; ever; in the whole history of everything. My friends this is the answer to life, the universe and everything. But what is it and why is it in this particular arrangement. The first 92 elements from Hydrogen to Uranium are naturally occurring. Of those 92, the first 26 are made in the centre of stars via nuclear fusion (I may do a quick article on this in the near future). Elements 27 to 92 are created when stars explode in a supernova where temperatures can reach hundreds of millions of degrees. The rest, from 93 onwards, have been made in labs around the world; you may be able to tell where by element names.

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Going back to key stage 3 and GCSE there are several main areas to the table. There are metallic and the non-metallic elements. The metals are the left of the zigzag line, in the green and turquoise area, and the non-metals to the right. There that’s key stage 3 chemistry.

These can be further broken down. The orange column (group 1) are called the alkali metals, the yellow (group 2) are the alkali earth metals. The block of elements in the middle is known as the transition metals. Elements in turquoise are poor metals and the green elements are non-metals. The blue column to the right (group 8 or 0) is known as the halogens. Group 7 also has a special name, they are referred to as the halogens. Elements in each group have different properties, reactivities and generally cool stuff about them but if I were to go into all of that I would be here for way too long.

The man we owe the most for creating this table is Russian all-time great lad Dmitri Mendeleev. This man was responsible for making the most important leap in addressing the categorisation of the elements. Mendeleev left blanks, spaces which he thought yet to be discovered elements would fit into. It had been known for a few years that each element had a different weight, something we owe to Jöns Jacob Berzelius. Mendeleev utilised this and also the fact that many elements have similar properties to create his magnificent table. Up until that point many scientists used either one or the other to order the elements. Mendeleev used both and whilst his first table wasn’t perfect it was pretty darn good.

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This was THE major step towards what we now think as the periodic table of elements.

But enough of how it was made, what makes it so wonderful.

Within the table there are many different patterns to see. The table is made up of 7 rows or ‘periods’ that show the number of electron shells around the nucleus and 18 columns or ‘groups’ that show the number of electrons it is outer most shell. For example Carbon is in period 2, group 4 so has two shells of electrons and four electrons in its outer most shell. Each electron shell can only hold a certain number of electrons. The first shell can hold only two, the next eight the, third is also eight however the fourth and fifth can hold 18 each and the sixth and seventh 32. Taking carbon again as our example, it has two electrons in the first shell but this is then full and so it moves to the next shell where it happily fits the other six electrons in.

The next fantastic thing about the modern periodic table is that these electron shells are then further divided into sub-shells. There are four sub shells S,P,D and F. like the electron shells these can only take a certain number of electrons. The S sub-shell can take two. The P shell six, the D shell can take another 10 before it is full and the F can take 14. These also fill up sequentially, so to drag carbon away from whatever it was doing again and take it as an example again. The first shell in a carbon atom can take two electrons as we have already seen and so it only needs the S sub shell before it is happy. The next shell up can take another eight so we need the S sub shell with two but that leaves us six electrons short, perfect for the P sub-shell and now the 2nd electron shell is happy. The third again needs S and P before it is full but the fourth electron shell needs to use up the D sub shell as well as the S and P. This continues on up to the sixth and seventh needing the F subshell as well. This has been a bit of a tangent but we are getting to the relevance to the table now. There are four main areas of the Periodic table. Groups 1 and 2 are called the S-block. The part between groups 3 and 8 is called the P-block, the transition metals are referred to as the D-block and the Lanthanides and Actinides are termed the F-block. This term relates to which sub-shell the outer electrons are situated in. In the S block the outer electrons are in the S sub-shell and so on. This further explains the reactivity of the groups.

This concludes my whistle stop tour of how the periodic table is structured, if you want to see how many you can name then please take this test: http://www.sporcle.com/games/g/elements. Come and find me if you think you have beaten my best!!!

T. Gloess

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