• Question: What is the periodic table of elements for?

    Asked by 329merf49 to Waqar, Melissa, Jenni, Catherine, Angus on 21 Jun 2016.
    • Photo: Melissa Ladyman

      Melissa Ladyman answered on 21 Jun 2016:

      That’s a great question. I’m going to cheat a bit and tell you why it’s useful for people like me who try to make new chemicals out of the ones we already have. The periodic table lets me find out very quickly what a particular element might be like. This is because the elements are arranged in a very special order- they are arranged into columns with elements that have similar properties all sharing a column.

      If I know what Lithium is like (a soft metal that reacts violently with water), then I can guess that Sodium and potassium will be similar.

      It gets better than that though! The elements are arranged in a particular order (generally they get bigger as you go down a column, and smaller as you go across a row) and we can predict what properties they will have. For example I know that sodium reacts more violently with water than lithium does, and potassium reacts even more quickly!

      We have a periodic table hanging on the wall in our lab so that we can quickly work out the atomic mass of the elements- that helps us work out how much of a particular chemical to put in our experiments!

      As to what was the periodic table originally for… well, as humans we naturally try to look for the rules and laws that make the world work so I guess the periodic table was a way to try and explain why elements act in a certain way. It’s certainly helpful!

    • Photo: Angus Cook

      Angus Cook answered on 21 Jun 2016:

      The periodic table is a useful way of grouping together and displaying the elements. The elements are made up of particles called protons and neutrons which are stuck together in what we call the ‘nucleus’. There are also electrons orbiting around the nucleus, a little bit like the planets around the Sun.

      (Have this open in another tab or window, it might help as I talk you through it.)

      (This one is interactive, but might be a bit cluttered, up to you which to look at)
      http://www.rsc.org/periodic-table

      We classify the elements by how many protons they have in their nucleus. We call anything with only one proton in the nucleus ‘hydrogen’, anything with two protons ‘helium’, anything with three ‘lithium’, four ‘beryllium’, five ‘boron’, and so on. On the periodic table we order the elements going left to right, top to bottom, a little like you’re reading words on a page.
      [Side note: The same element (i.e. hydrogen) can have different numbers of neutrons in the nucleus AND STILL be the same element. Remember, it’s all about the number of protons!]

      Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. The charges on a proton and an electron are equal, so if you have one proton and one electron, you have two opposite charges which cancel each other out. In general it’s easier for the elements to exist with a neutral charge (i.e. cancelled out charges) so the elements usually have the same number of electrons as they do protons.

      So again going from left to right, top to bottom, hydrogen has 1 electron, helium has 2 electrons, lithium has 3 electrons, beryllium has 4 electrons, and so on…

      Now, the way the different elements are grouped together tells you something about how the electrons are arranged around the nucleus. As you add more and more electrons they have to come up with different ways to sit around the nucleus (they can’t just all sit in the same place!).

      The language can get a bit complicated but one way to think about it is to add electrons to an atom (lets say an aluminium atom).
      Add the first one, and it sits nice and close to the nucleus. We add another, and there’s still space next to the nucleus for that one too.
      Now we want to add the third, but there’s no more space next to the nucleus. We have to put this next electron a little further away. This is why the 3rd electron starts a new row on the table. The fourth can sit next to the third, but the next six electrons all have to be added in a slightly different way (this is why the second row is split into two bits, on the left with lithium and beryllium, and on the right with boron to neon).
      This has brought us up to ten electrons. Now if we want to add an eleventh there’s no more room where we added the others, so we need to move a little further away from the nucleus and start again. So we put the 11th electron (which sodium (Na) needs onto another row again.

      We can use the periodic table to predict the chemical properties of elements, and it was even used in the past to predict the existence of elements which we’d not yet discovered (because there was a hole in the table)

Comments