dat 2007 science #67

[Hope30]

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The question reads, he electronic configuration of a particular neutral atom is 1s^2 2s^2 2p^6 3s^2 3p^2. What is the number of unpaired electrons in this atom?
Answer: 3
How? I know it is Si with three subshells, so 3p^2 has two electrons to occupy two of the three subshells. For that reason, i pick 2. Then, i think maybe 3s^2 can excite one e- to occupy the third subshell, but that still makes four unpaired e-. I dont know how they get 3 as an answer. Thanks for the help.

 

[AlbinoPolarBear]

The question reads, he electronic configuration of a particular neutral atom is 1s^2 2s^2 2p^6 3s^2 3p^2. What is the number of unpaired electrons in this atom?
Answer: 3
How? I know it is Si with three subshells, so 3p^2 has two electrons to occupy two of the three subshells. For that reason, i pick 2. Then, i think maybe 3s^2 can excite one e- to occupy the third subshell, but that still makes four unpaired e-. I dont know how they get 3 as an answer. Thanks for the help.

It's 2. Answer key is wrong.

 

[Hope30]

Thanks 👍