Why is the first ionization energy of a nonmetal much higher than that of an alkali metal in its same period?
The first ionization energy (first IP) generally increases as one moves from the left to the right on the periodic table (in the same period). That's because the nuclear charge in increasing but the added electrons are going into the same shell so the attractive force is higher.
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The first ionization energy refers to the amount of energy needed to remove an electron from an atom in its gaseous state. The first ionization energies of nonmetals are generally higher than those of alkali metals in the same period due to a few important factors.
Firstly, nonmetals have higher effective nuclear charges compared to alkali metals. Effective nuclear charge refers to the attraction between the positively charged nucleus and the negatively charged electrons. Nonmetals have more protons in their nucleus, leading to a stronger attractive force on the outermost electrons. This increased attractive force makes it more difficult to remove an electron, resulting in a higher ionization energy.
Secondly, nonmetals have smaller atomic radii compared to alkali metals in the same period. Atomic radius refers to the size of an atom. The smaller the atomic radius, the closer the outermost electrons are to the nucleus, and the stronger the attractive force between them. As a result, nonmetals have higher ionization energies because the electrons are held more tightly, requiring more energy to remove them.
Lastly, nonmetals tend to have a higher number of valence electrons compared to alkali metals. Valence electrons are the electrons present in the outermost energy level of an atom. As nonmetals have more valence electrons, it takes more energy to remove an electron since there is a stronger interaction between the electrons and the nucleus.
Therefore, the combination of higher effective nuclear charges, smaller atomic radii, and larger numbers of valence electrons makes the first ionization energy of nonmetals much higher than that of alkali metals in the same period.