For a multielectron atom, a 3s orbital lies lower in energy than a 3p orbital because (LO 5.16) (a) a 3p orbital has more nodal surfaces than a 3s orbital. (b) an electron in a 3p orbital has a higher probability of being closer to the nucleus than an electron in a 3s orbital. (c) inner electrons shield electrons in a 3p orbital more effec-tively than electrons in a 3s orbital. (d) the energy of the electron can be spread between three 3p orbitals instead of only one 3s orbital.

Video transcript

Welcome back everyone. We need to explain why an electron in the two p orbital has a higher energy than an electron in a two s orbital. We're going to first think of a concept known as effective nuclear charge represented by the symbol ZF. And we want to recall that this is characterized by electrons which experience a pull towards the nucleus of an atom based on this charge. So again ZF is effective nuclear charge. And this makes sense because we want to recall that within our atom, our nucleus at the center contains our protons and neutrons inside. But on the outside of our nucleus lies our electrons. Where specifically we want to recall that our valence electrons which is our outermost or make up our outermost shell of electrons because these are our outermost electrons are valence electrons are shielded bye inner electrons. So our core electrons let's be more specific and say by core electrons. And so with this understanding we can say that an increase of electrons will correlate to an increase in the shielding effect that is experienced by our valence electrons which is therefore going to increase the energy of our valence electrons. So considering what our prompt mentions, we have first our two s orbital and thinking of R two S orbital, we want to recognize that two tells us that we are at our second level of our sub level here, our second sub level which is therefore going to be shielded by the previous sub levels, electrons so shielded by one s electrons. But now considering our two p orbital, we want to then recognize that this is going to be shielded by the previous sub levels electrons being our two s orbital electrons So shielded by and also shielded by our one s orbital electrons because we know we can't get to the two P orbital without passing through our one S and two S sub levels on our periodic table, recall our electron configurations when we are doing things like that, moving through each sub level. And so we can see that R2P orbital is shielded by more than one sub level, meaning that we have increased shielding here. So we would say you have increased Shielding of R two P orbital Or of the valence electrons in the two p orbital. And due to this increased shielding shielding we would say therefore our two p orbital's have higher energy and therefore a lower attraction or we can say a lower effective nuclear charge. So the effective nuclear charge being lower means that that pull towards the nucleus is going to be weakened or be less attractive for those electrons. So for our final answer, based on what we've outlined, we can confirm that the correct choice would be choice B which states that electrons in the two p orbital experience less attraction to the nucleus, which is why our two p orbital has higher energy. I hope that everything I reviewed was clear. If you have any questions, please leave them down below and I'll see everyone in the next practice video.