Merry Meet,
I believe the four elements are still relevant even after the discovery of the periodic table of elements. Other lesson sixes written by others in the clan have explained this point of view far better than I can (namely Melissa who lost me at points with her fantastic, but very scientific lesson on the elements J ). However I have done my best and the lesson as I have written makes sense to me, even if I seem to ramble at points.
The periodic elements are the make-up of the four major elements. For example oxygen and hydrogen are water, one of the major elements. All of the elements in the periodic table of elements can also be seen to correspond to one or more of the four major elements. Well for me they would relate to at least one of the main elements, they would be either an element concerned with air, water fire and earth. They can also belong to more than one main element. For example oxygen would be classified into the air category, but when coupled with Hydrogen it becomes a water element.
The periodic table didn't actually invent any new elements that never existed before; it just classified and named them differently. The Ancient Chinese even categorized their main elements differently. In addition to Fire, Water, Earth and Air they had Metal as an element. In so many cultures the four categories of elements remained. People can still relate to and understand the four main elements, but not everyone even knows every element on the periodic table. Everyone being able to identify with the four main elements is one of the basic reasons that they are still relevant. It is due to that fact that everyone can relate to the four major elements, and not the periodic table, that the major elements have remained relevant. I found myself understanding this concept more by likening it to the concept of deity. Almost everyone in the world regardless of religion can relate to a divine power of some description. This correlates to all cultures being able to understand and identify with the four main elements. However once one looks at every god in every religion, and even looks at every deity that could be worshipped in a Wiccan sense, it can be seen that being able to comprehend that many forms of deity is very difficult. One cannot even begin to know every deity, let alone be able to work with every one. Trying to work with every known deity is impossible as well as impractical. This to me shows how one can understand the four main elements, but would be far stretched to be able to apply the whole periodic table of the elements to a ritual. People casting ritual would probably not very often have to call upon every single element like Sodium or Chlorine if the whole periodic table was to be used in ritual! Plus every deity is just an aspect of the one divine power, just like every periodic element can be associated with a main element. Hence by using the main elements in ritual we are encompassing the whole, and celebrating every individual piece of that element.
It will be noticed that I haven't included Spirit as one of the major elements. For me this does not relate to a comparison between the main elements, and the periodic table. As I see it, Spirit is encompassed in all the elements and will always be relevant to every living creature.
I know that this isn't the way in which others have chosen to answer this question but for me it makes the most sense. All cultures understand basic elements, and every periodic element can be classified into one of the main elements. Hence the four main elements for me are still extremely relevant. I am going to undertake further research into this in my spare time. I know that Laurie Cabot teaches Wicca as Science, so I will read up and see if she has written any information on this topic. I will also look in some other resources that I think may be helpful. I didn't do it all before writing this lesson as it is something on which I wish to take a lot of time, and may be one of those subjects that I research for years to come.
Blessed Be Miw Sheri