In this video, we're going to take a look at the first type of exceptions that exist for certain transition metals. Here we're going to say starting from chromium. So chromium is right here. As the atomic number Z increases, exceptions to electron configurations can be observed. So our memory tool here is that chromium has an atomic number of 24, and there are two and four. So we have these two elements that have this type of exception, version one, and then these four here O to get the other column.
Remember to skip next 4. All right, so here we're going to say 2. So we're starting with Chromium, and then we skip the next 4. And then here goes our group of four. Now all of these elements have our shell number N and all of them have one electron in their S orbital, so those will be N South to the one. If we take a look here, we're going to say an S orbital electron can be promoted to create half filled orbitals with D4 and D9 elements.
So if we were to look at the electron configurations of these, these would be D4 initially and these would be D9 initially before the promotion of an electron from the S orbital. So for example, if we took a look at chromium, chromium has an atomic number of 24. We would think that its electron configuration is argon 4S23D4. But again, since it's an exception one type transition metal, one of the electrons from the S orbital would get promoted over to our D.
So now its electron orbital diagram would look like one in the 4S and five electrons in the 3D orbitals, giving us a new electron configuration of argon 4S13D5. Just remember when it comes to these elements in particular they fit under exception one, they are D4 and D9 elements. But because of the promotion of an electron from the South orbital, we change the D4s into D5 as we see here and D9s would become D10s all right. So just remember these particular elements under this first type of exception.
