Question

Would you expect the valence electrons of rubidium and strontium to reside in the \(5 s\) or the \(4 d\) orbitals? Why?

Short answer

The valence electrons of rubidium and strontium reside in the 5s orbitals. This is because the 5s orbital has a lower energy than the 4d orbital, and electrons fill lower-energy orbitals before higher-energy ones, according to the Aufbau principle. The electron configurations are \(Rb: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^1\) and \(Sr: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2\).

Step-by-step solution

Determine electron configurations

The first step is to find the electron configurations for both rubidium and strontium. We can accomplish this by referencing the periodic table and applying the aforementioned principles. Rubidium (Rb) has an atomic number of 37, which means it has 37 electrons. Similarly, strontium (Sr) has an atomic number of 38, which means it has 38 electrons. The electron configuration of rubidium can be written as follows: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^1\) And the electron configuration of strontium is: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2\)

Identify the valence electrons

Valence electrons are the electrons in the outermost energy level of an atom. From the electron configuration of rubidium (Rb), we can see that the outermost energy level is n=5, and only the 5s orbital has electrons in that level. There is one electron in the 5s orbital. In the case of strontium (Sr), the outermost energy level is also n=5, and there are two electrons in the 5s orbital.

Determine the location of valence electrons

Given the electron configurations we obtained in Step 1 and the determination of the valence electrons in Step 2, we can now conclude the location of the valence electrons for rubidium (Rb) and strontium (Sr). For rubidium, the valence electron resides in the 5s orbital. For strontium, both valence electrons reside in the 5s orbital. Therefore, the valence electrons of rubidium and strontium reside in the 5s orbitals, not the 4d orbitals. The reason is that the 5s orbital has a lower energy than the 4d orbital, according to the Aufbau principle, and electrons fill lower-energy orbitals before higher-energy ones.