#### Video

## 2.7 Quiz Video Solution (2.4 – 2.7)

#### Lesson Summary

1. Which of the following electron configurations represents an element in an excited state?

A. 1s^{2}2s^{2}2p^{5}

B. 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{8}

C. 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}3d^{5}

D. 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{5}

E. 1s^{2}2s^{2}2p^{6}3s^{2}3p^{2}4s^{1}

2. How many unpaired electrons are present in the +2 cobalt ion, Co^{2+}, in its ground state?

A. 2

B. 3

C. 4

D. 5

E. 6

3. Please indicate which element corresponds to each of the following *electron configurations*. How many unpaired electrons does each one have?

A. 1s^{2}2s^{2}2p^{6}

B. 1s^{2}2s^{2}2p^{5}

C. [Kr]5s^{1}4d^{5}

D. [Ar]4s^{2}3d^{10}4p^{4}

4. Why is each of the following ** electron configurations** incorrect for atoms in their ground states? How could you correct each of these?

A. 1s^{2}2s^{2}3s^{2}

B. [Ar]3s^{2}3p^{3}

C. [Ar]4s^{2}4d^{3}

5. Please write the electron configuration of each of the following elements:

A. Oxygen

B. Potassium

C. Arsenic

D. Manganese

E. Copper

6. Please write the *condensed electron configuration* of each of the following elements:

A. Fr

B. Br

C. Ca

D. Zn

E. Ce

F. Se

#### Lesson

2.7 Quiz Video Solution (2.4 – 2.7)

#### Instructor

Dr. Christiansen is a chemistry professor at Utah State University and has a PhD in organic chemistry. He's been teaching students chemistry for nearly 12 years.