Among the following, which element has the lowest ionization energy?
A. Na
B. Cl
C. Cs
D. I
Lowest ionization energy. Lower left on periodic table.
Highest. Upper right (not counting group VIII; i.e., group 18.)
To determine the element with the lowest ionization energy among Na, Cl, Cs, and I, we need to understand what ionization energy is.
Ionization energy is the amount of energy required to remove an electron from a neutral atom in its gaseous state. It represents how tightly an electron is held by the nucleus of an atom.
Generally, as we move across a period from left to right in the periodic table, the ionization energy increases because the number of protons in the nucleus and the electron shielding stays the same, but the number of electrons increases. This results in a stronger attraction between the nucleus and the electrons, making it harder to remove an electron.
Similarly, as we move down a group in the periodic table, the ionization energy tends to decrease because the outermost electrons are farther away from the nucleus, resulting in a weaker attraction.
Let's analyze the options:
A. Na (sodium) - Sodium is located in group 1 (Alkali metals) and period 3 of the periodic table. It has 11 protons and 11 electrons. Compared to the other elements in the options, sodium has a relatively low ionization energy due to its position in the first group. However, there are other elements in the list that are expected to have lower ionization energy than sodium.
B. Cl (chlorine) - Chlorine is located in group 17 (Halogens) and period 3 of the periodic table. It has 17 protons and 17 electrons. Chlorine has a higher ionization energy due to its position in the second-to-last group (towards the right side) of the periodic table.
C. Cs (cesium) - Cesium is located in group 1 (Alkali metals) and period 6 of the periodic table. It has 55 protons and 55 electrons. Cesium has a larger atomic radius and is farther from the nucleus than sodium, making it easier to remove an electron. Therefore, cesium is expected to have lower ionization energy than sodium.
D. I (iodine) - Iodine is located in group 17 (Halogens) and period 5 of the periodic table. It has 53 protons and 53 electrons. Iodine has a smaller atomic radius than cesium, which makes it harder to remove an electron. Thus, iodine is expected to have a higher ionization energy compared to cesium.
Considering the explanations provided, the element with the lowest ionization energy among the given options is C. Cs (cesium).