Final answer:
K (potassium) has the lowest first ionization energy among the given elements due to its position on the periodic table. Potassium is the lowest in the group of alkali metals, indicating that its valence electron is less tightly bound and easier to remove compared to sodium, calcium, and the noble gas argon.
Step-by-step explanation:
Lowest First Ionization Energy
The student asked which of the following elements has the lowest first ionization energy: K (potassium), Ca (calcium), Na (sodium), or Ar (argon). To answer this question, we utilize our understanding of ionization energy and its trend on the periodic table. Ionization energy is the energy required to remove an electron from a gaseous atom or ion.
In general, ionization energies increase across a period (from left to right) and decrease down a group (from top to bottom) on the periodic table. This pattern is because electrons added in the same shell do not shield each other effectively from the nuclear charge, and electrons added in higher shells are farther away from the nucleus and thus, less tightly held.
When we look at our options, K, Ca, Na, and Ar, we should first notice that argon is a noble gas with a complete outer electron shell, which gives it a very high ionization energy. Thus, Ar would have the highest ionization energy among the given elements. Sodium (Na) and potassium (K) are both in the same group (alkali metals), but potassium is lower on the periodic table, which means it should have a lower ionization energy than sodium. Calcium (Ca) is in a different group and has two more protons than potassium, which typically would mean a higher ionization energy due to a stronger nuclear charge.
Therefore, it can be concluded that K (potassium) has the lowest first ionization energy among the given elements due to its position lowest and furthest to the left in the periodic table. This is supported by the periodic trends and the fact that it has a single valence electron in a higher energy level compared to the others, making it easier to remove.