Final answer:
Cesium has the lowest ionization energy among Helium, Fluorine, Sodium, and Cesium due to its position in the periodic table. It is an alkali metal located at the bottom left, which correlates with lower ionization energies.
Step-by-step explanation:
The element with the lowest ionization energy among the choices given (Helium, Fluorine, Sodium, and Cesium) is Cesium. Ionization energy tends to decrease as we move down a group in the periodic table. Cesium is located in the bottom left corner of the periodic table, which means it has lower ionization energy than elements higher up or to the right. This is because Cesium has more electron shells, making it easier for the outermost electron to be removed due to the increased distance from the nucleus and the weaker attraction.
Additionally, comparing the elements provided in other examples, such as Lithium, Nitrogen, and Iodine, we find that rubidium (Rb), which is similar to Cesium in its position on the table, also has a low ionization energy. Elements in Group 1, like Cesium and Rubidium, are known as alkali metals and tend to have low ionization energies. In contrast, a halogen like Fluorine has high electronegativity and higher ionization energy. Noble gases like Helium have full energy orbitals and also high ionization energies.