For anyone who regularly follows my blog, or for those I interact with regularly I must apologise – if you follow my twitter you will know I got marooned on the small island of Jersey this week which through everything off kilter – my studies, my running, my blog and my German. Schade! Anyhow, I am back in the comfort of my small little flat in London now, having done the weeks washing and caught up with my degree work so let’s get going again.
I am currently fulfilling the Chemistry requirements of my generalist science section, which I do find fairly enjoyable. I have to say however there is an inner frustration you have to wrangle with when studying Chemistry because there are large patches of it for which we don’t know why it happens. We have the rules very well pinned down and we can say that action A happens because of rule B, however why rule B should even be a rule in the first place is sometimes, but not always ambiguous. That said – it is a great subject and not one that should be overlooked by scientists in any discipline.
I imagine there are going to be quite a number of posts from me on Chemistry related themes over the next few weeks, given the studies I am doing, but for today I thought it would be good to introduce some of the basic concepts of the periodic table. I am not going to be going to go into basic detail on the periodic table – I assume a very simple working knowledge but if you do find any of it confusing, just ask.
Group 1 metals
Anyone who took Chemistry at GCSE level will probably remember playing with group one metals, dropping them into water and observing reactions similar to these (the less extreme ones anyway).
Group one metals are interesting metals indeed – they are soft metals that quickly go dull when left to react with Oxygen. The most interesting thing about them is the explosive reaction they have when they react with water and the reason for this is very simple. Take a look at the electron configuration of sodium:The most important thing here is that there is a valence shell (here the subshell 3s) where there is just one electron. This means in order to obtain a more stable electron configuration mirroring that of the noble gases they only need to loose one electron – this is fairly “easy” so the group one metal will easily shed this electron. The metal is so reactive it is often not found as a pure metal on Earth, but rather in compounds such as the ionicly bonded NaCl. The most common way to produce the metal is through electrolysis. As you go down the group, the reactivity increases (which is obvious because the s subshell with one electron goes further away from the nucleus).
All group one metals will react with chlorine to form white solid compounds of the format one group one metal for every one chlorine atom (this is just an example of one of many chemical reactions)
Examples are sodium, potassium and francium.
Group 2 metals
The alkaline earth metals exhibit very similar properties – except rather than having one electron in the valence shell they have two. This of course means that they have lower reactivity, although they still are highly reactive. The group two metals would react with things like oxygen with one group 2 metal for every 2 oxygen.
All group two metals will also react with chlorine – but since the valency of chlorine is unchanged, but our group 2 metals need to shed two electrons we are left with two chlorine atoms for every one group two metal. Take a look at the reaction in the Lewis diagram structure.Examples are Beryllium and Magnesium.
The transition metals go from group 3 through to group 12 and contain 38 metals. In general there is less to say about these – that isn’t necessarily because the chemistry is any less rich or interesting it is more a result of the fact that the rules are much less prevalent – I can’t give the same quick rules and characteristics like I can for group one or two metals. There are some things that are generally true of the transition metals however;
- They are malleable and ductile;
- They are conduct both heat and electricity; and
- The electrons they use to bind with other atoms are found in more than one subshell.
It is this last point which is why they don’t observe such screamingly obvious logic, but if you think about they way electron subshells are filled, you were bound to get to scenarios where this happened. Iron, cobalt and nickel are the standout transition metals, since they are the only metals known to produce a magnetic field.
This is the Boron family, which tend to favour +3 oxidation states – they need to shed three of their outer electrons to achieve stability.
This is carbons family, one of the most abundant elements which shapes all life as we know it. These elements will readily form compounds. They have a valency of four, which means when you react say carbon and hydrogen together you get methane – CH4. I actually think it is quite inspiring to look at carbon:
Now just think how this impacts everything and everyone around you. Here is a list of some carbon compounds;
- carbon dioxide (CO2)
- carbon monoxide (CO)
- chloroform (CHCl3)
- carbon tetrachloride (CCl4)
- methane (CH4)
- ethylene (C2H4)
- acetylene (C2H2)
- ethyl alcohol (C2H5OH)
- acetic acid (CH3COOH)
The list really could go on forever – but glucose if a very important emission from this list, which clearly is everything for humans – it is the petrol we run on. I hope you are getting the point with valency that all of these elements in the group have the same valency. So because I have told you what carbon does you can work down the group and consider other elements – the valency is the same.
First is the nitrogen family – which is a fairly important family because nitrogen is the first sufficiently electronegative element to be able to participle in electron bonding. Next we have the oxygen family and finally the halogens. What to observe is that the top element in the three groups can participate in hydrogen bonding – this will become slightly clearer considering general trends.
Overall the valency of the group is 3,2,1 as we go across – hence indicating why chlorine could appear in the above as NaCl however we need CO2 in order to get the chemistry to work.
Another thing to note is that these groups are not metals – which makes them distinct from earlier groups.
The Noble gases – the perfect atoms. I like the word noble for these, it’s so loaded with personification. You can just imagine these atoms with perfect electron configuration that have been awarded with noble status while the ordinary imperfect atoms run around trying to be like them… this is exactly what happens. The noble gasses have a full valency shell which shields them from participating in any chemical reactions.
This is not quite true – with a huge amount of energy you can add or remove electrons from a noble gas, however for all intents and purposes they are un-reactive.
You should also note the following trends when trying to understand the table:
- From left to right across a period of elements, electronegativity increases.
- From top to bottom down a group, electronegativity decreases.
- Important exceptions of the above rules include the noble gases, lanthanides, and actinides.
There are lots of other trends – too many to list out, but they will come in future posts as we examine the materials in more detail. For today, I just wanted to do a whistle stop tour of the table. I know I have dropped in a huge number of terms with no explanation – but do ask if you have a question. Let me know other cool trends I didn’t mention – I ran out of time!