2.33 and 2.1 [ENDORSED]

[Lindsay H 2B]

Which of the following increase when an electron in a lithium atom undergoes a transition from the 1s-orbital to a 2p-orbital? a) energy of the electron. b) value of n. c) value of l. d) radius of the atom. Compare your answers to the answers of ex 2.1 (2.1 asks essentially the same thing about a hydrogen atom instead of a lithium atom).

The solutions manual says that for both lithium and hydrogen, all the options increase but I don't understand why the radius of the atom would increase for lithium. In its ground state, lithium already has an electron at the n=2 energy level, so I don't understand why exciting another electron to that energy level would increase the radius at all for lithium.

[RuchaDeshpande1L]

From what I understand, I think the atomc radius increases because the electron is getting arther away from the nucleus and thus does not feel the pull of the positively charged nucleus as strongly. The electron starts in the n=1 shell, as part of the 1s subshell. Once excited to the n=2 shell, or 2p subshell, the negatively charged electron moves away from the nucleus and "feels" its attraction less. As a result, the overall atomic radius expands because the nucleus is not pulling the electrons in as much as when there was an electron closer to the nucleus, in n=1.