Final answer:
The first ionization energy for the element with atomic number 37, rubidium, decreases due to its position in the periodic table within a group where elements exhibit lower ionization energies as we move down the group.
Step-by-step explanation:
The atomic number 37 corresponds to the element rubidium. On the periodic table, rubidium is located in the first group, which is known for having low first ionization energies due to their valence electron being far from the nucleus in the outermost shell. As one moves down a group in the periodic table, the first ionization energy generally decreases. This is because the valence electrons are further from the nucleus due to additional shells, and the increased distance reduces the electrostatic attraction between the nucleus and the valence electron. Therefore, it becomes easier to remove an electron and the ionization energy is lower.
In the case of rubidium, when comparing it to other elements in the same group but with lower atomic numbers, it can be predicted that its first ionization energy would be lower than those of its preceding elements in the group, such as potassium (atomic number 19). Hence, for rubidium, the first ionization energy decreases.