 The last thing that I want to go through with you is that one of the problems students often have is remembering the order of the orbitals when they're writing electron configurations. Happily, you can actually just read the order of the orbitals from the structure of the periodic table. First of all, recall that the periods in the periodic table tell you the energy level. So hydrogen and helium have their electrons in level one. Lithium and beryllium, et cetera, et cetera, reach up to level two. When you get up to sodium and magnesium and so on, they're in level three and so on. The second thing is that the element groups can be divided up into blocks. The first two groups, group one and group two, are called the S block. This is because all the elements in this block have their outermost valence electrons in an S orbital. The right hand side, coloured orange, is called the P block. All the elements in this block have their outermost valence electrons in a P orbital. The green transition metals are called the D block for the same reason. Their outermost valence electrons are in a D orbital. So if you read through the periodic table in order of atomic number, it will show you the order of the orbitals. Starting at hydrogen and helium, and helium has been put in this slightly odd place to show that it is part of the S block. So starting with hydrogen and helium, you have the 1S orbital. You then move to level two, so period number two. So the next elements, lithium and beryllium, they're still in the S block, so they're 2S. Moving across the period, we're still in level two, but we're now into the P block, so these are the 2P orbitals. So I've gone 1S, 2S, 2P. Moving into the next period, we have the 3S orbitals, and then across further and we get the 3P orbitals. After this is when things get a bit tricky, but we can leave this for a higher level course.