Electron Configurations

Question

Answer the following questions about the electron configuration given below.

↑ ↓ ↑ ↑ ↓ ↑ ↓ ↑ ↓

___ ____ ___ ___ ___

1s 2s 2p

What element can have this configuration? (2) ______________________

Is this configuration a ground, excited, or forbidden state? Explain your answer. (4)

configuration: ______________________

Answer 1

 Looking at the configuration as presented, there are 9 electrons with a filled 1s but an unfilled 2s, even though there are electrons in the 2p subshell. With 9 electrons, and being an element and not an ion, this would have to be fluorine (but see below).

The ground state for F is 1s2 2s2 2p5. The given configuration does not follow the Aufbau principle of filling the lowest energy orbital before entering a higher energy level (here the 2p is filled before the 2s). This could be considered an EXCITED state of fluorine, although this is usually accomplished by promoting the 2p electron to the 3s orbital.