Which element has the highest first ionization energy?

First ionization energy refers to the energy required to remove the outermost electron from a neutral atom. In the context of the periodic table, ionization energy typically increases as you move from left to right across a period and decreases as you move down a group.

Fluorine is located in the second period of the periodic table and is one of the halogens, known for their very high electronegativity and ionization energies. The small atomic radius of fluorine means that its valence electrons are held tightly by the nucleus, requiring a significant amount of energy to remove one of these electrons.

While both hydrogen and neon are also in the second period, hydrogen has a lower ionization energy due to its single electron relatively far from the nucleus and absence of a full valence shell. Neon, though it has a higher ionization energy than many other elements, is a noble gas with a fully filled outer shell which, compared to fluorine, results in a lower first ionization energy because it is less inclined to lose an electron.

Nitrogen, while it has a notable ionization energy as well, does not surpass that of fluorine. The repulsion between electrons in nitrogen’s half-filled p orbital leads to a slightly lower ion