Write the equation for the first ionization energy of silver. Include all states and charges. Include the energy term as IEi. The first ionization energy of silver is 731 kJ/mol. Compare this to rubidium’s ionization energy in the textbook or online. Would you have predicted this relationship using periodic trends? Why or why not
The Correct Answer and Explanation is:
First Ionization Energy of Silver (Ag)
Equation:
Ag(g) + IE₁ → Ag⁺(g) + e⁻
Where the first ionization energy (IE₁) is 731 kJ/mol.
Explanation and Comparison
The first ionization energy (IE₁) is the minimum energy required to remove one mole of the most loosely held electrons from one mole of neutral gaseous atoms to produce one mole of gaseous ions with a +1 charge. For silver, this energy is 731 kJ/mol.
Comparing this value to the first ionization energy of rubidium (Rb), which is 403 kJ/mol, it is clear that silver’s ionization energy is substantially higher. This relationship is predictable based on established periodic trends.
Ionization energy generally increases from left to right across a period on the periodic table. Both rubidium and silver are in the fifth period. Rubidium is an alkali metal in Group 1, while silver is a transition metal in Group 11. As one moves across a period, the number of protons in the nucleus increases, resulting in a greater positive nuclear charge. For Period 5, rubidium has 37 protons (Z=37), whereas silver has 47 protons (Z=47).
This increased nuclear charge attracts the electrons in the atom more strongly. Although additional electrons are also being added, they occupy the same principal energy level (or, in the case of transition metals, the inner d-subshell). These added electrons do not completely shield the valence electrons from the pull of the increasingly positive nucleus. The net result is a higher effective nuclear charge (Zeff) experienced by the outermost electron.
In silver, the single 5s valence electron is pulled much more powerfully by the 47 protons in its nucleus than the 5s valence electron in rubidium is by its 37 protons. The ten 4d electrons added across the transition series are poor at shielding, making the increase in Zeff particularly pronounced. Consequently, significantly more energy is required to overcome this stronger attraction and remove an electron from a silver atom compared to a rubidium atom. Therefore, the observation that silver’s first ionization energy (731 kJ/mol) is nearly double that of rubidium (403 kJ/mol) is entirely consistent with periodic trends.
