I'd like to share with you how to determine the number of valence or outer shell electrons looking at the periodic table and also looking at an electron configuration. So here's carbon. The electronic configuration for carbon is 1s2 2s2 2p2. The number of valence electrons in carbon is 4. And that's determined by looking at the electron configuration and noting that the outer sub-shells are associated with the highest principal quantum number. And that is in this case 2 is the highest principal quantum number. And there are 2 electrons in the 2s sub-shell and there are 2 electrons in the 2p sub-shell. We can also look at the periodic table and find the principal quantum number, the highest principal quantum number by looking at which period we're in. And if carbon is in the second period, we count the electrons associated with the 2s, which is 2, and the electrons associated with the 2p, which is 2. Here's another example. Arsenic. A bit more complicated electron configuration, but all be it, we handle it the same. Now here, this represents the electron configuration as far as the fill-loader. But we need to pay close attention to the highest principal quantum number here and that's 4. And we have a 4s sub-shell and we have a 4p sub-shell. We ignore the 3d sub-shell. So we look at the electrons in the 4s, which is 2, and there are 3 electrons in the 4p sub-shell. So collectively, there are 5 electrons, outer electrons associated with arsenic. Also, we can look at the periodic table and see that arsenic is here in the 4th period. And there's 1, 2, 3 electrons in the p. Skipping over this 3d, we look at what's in the 4s and there are 2 electrons here.