Chapter 2 - Exercises - Page 99d: 83

a. Sodium (\( \mathrm{Na} \)) has 1 unpaired electron in the 3s orbital. b. Cobalt (\( \mathrm{Co} \)) has 3 unpaired electrons in the 3d orbital. c. Krypton (\( \mathrm{Kr} \)) has 0 unpaired electrons as all the orbitals are fully filled.

To determine the number of unpaired electrons in each element, we look at the last subshell (highest energy level) in the electron configuration. a. Sodium (\( \mathrm{Na} \)) has an atomic number of 11. The electron configuration for sodium is 1s² 2s² 2p⁶ 3s¹. To represent this electron configuration using an atomic orbital diagram, we can use boxes to represent the orbitals and arrows to represent the electrons. The first energy level (n=1) has only one orbital, the 1s orbital, which can hold a maximum of 2 electrons. So, we draw a box and put 2 arrows in it to represent the 1s² configuration. The second energy level (n=2) has three orbitals: the 2s orbital and the three 2p orbitals. The 2s orbital can hold a maximum of 2 electrons, so we draw a box and put 2 arrows in it to represent the 2s² configuration. The three 2p orbitals can hold a maximum of 6 electrons, so we draw three boxes and put 6 arrows in them to represent the 2p⁶ configuration. The third energy level (n=3) has one orbital, the 3s orbital, which can hold a maximum of 2 electrons. So, we draw a box and put 1 arrow in it to represent the 3s¹ configuration. The atomic orbital diagram for sodium is: ``` 1s ↑↓ 2s ↑↓ 2p ↑↓ ↑↓ ↑↓ 3s ↑ ``` b. Cobalt (\( \mathrm{Co} \)) has an atomic number of 27. The electron configuration for cobalt is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷. To represent this electron configuration using an atomic orbital diagram, we follow the same process as above. The atomic orbital diagram for cobalt is: ``` 1s ↑↓ 2s ↑↓ 2p ↑↓ ↑↓ ↑↓ 3s ↑↓ 3p ↑↓ ↑↓ ↑↓ 4s ↑↓ 3d ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑ ``` c. Krypton (\( \mathrm{Kr} \)) has an atomic number of 36. The electron configuration for krypton is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶. The atomic orbital diagram for krypton is: ``` 1s ↑↓ 2s ↑↓ 2p ↑↓ ↑↓ ↑↓ 3s ↑↓ 3p ↑↓ ↑↓ ↑↓ 4s ↑↓ 3d ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑ 4p ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ 5s ↑↓ 4d ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑ 5p ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ```