Problem 43 - Chemistry: The Central Science

Question

(a) What is the general relationship between the size of an atom and its first ionization energy? (b) Which element in the periodic table has the largest ionization energy? Which has the smallest?

Step-by-Step Solution

Answer

(a) The general relationship between the size of an atom and its first ionization energy is that as the size of an atom increases, the ionization energy decreases. This is due to the weaker attraction between the nucleus and the outer electrons in larger atoms, as well as increased electron shielding. (b) The element with the largest ionization energy in the periodic table is helium (He) due to its small atomic size and strong attraction between the nucleus and its electrons. The element with the smallest ionization energy is francium (Fr) because of its large atomic size, weak attraction between the nucleus and outer electrons, and substantial electron shielding.

Step 1: (a) General relationship between atom size and ionization energy.

The ionization energy of an atom is the amount of energy required to remove an electron from the outermost shell of an isolated gaseous atom. In general, as the size of an atom increases, the ionization energy decreases. This is because larger atoms have more electron shells, so the outer electrons are farther away from the nucleus. The positive charge of the nucleus has a weaker hold on the outer electrons, making it easier to remove them, and thus the ionization energy decreases. Additionally, larger atoms have more electron shielding, which also weakens the attraction between the nucleus and the outer electrons, leading to lower ionization energies.

Step 2: (b) Element with the largest ionization energy

The element with the largest ionization energy in the periodic table is helium (He). This is because helium has the smallest atomic size among all the elements and only has two electrons, both of which are in the first electron shell, closest to the nucleus. The strong attraction between the nucleus and the electrons makes it difficult to remove an electron, so helium has the highest ionization energy.

Step 3: (b) Element with the smallest ionization energy

The element with the smallest ionization energy in the periodic table is francium (Fr). This is because francium has the largest atomic size, with many electron shells and weak attraction between the outermost electrons and the nucleus. In addition, the many electron shielding layers in francium further weaken the attraction between the nucleus and the outer electrons. As a result, it requires the least energy to remove an electron from a francium atom, and francium has the smallest ionization energy of all the elements.