Question

Thallium (Tl) is a neurotoxin and exists mostly in the Tl(I) oxidation state in its compounds. Aluminum (Al), which causes anemia and dementia, is only stable in the Al(III) form. The first, second, and third ionization energies of \(\mathrm{Tl}\) are \(589,1971,\) and \(2878 \mathrm{~kJ} / \mathrm{mol},\) respectively. The first, second, and third ionization energies of \(\mathrm{Al}\) are \(577.5,1817,\) and \(2745 \mathrm{~kJ} / \mathrm{mol},\) respectively. Plot the ionization energies of \(\mathrm{Al}\) and Tl versus the number of electrons removed and explain the trends.

Short answer

Al favors +3 state, while Tl favors +1 due to differences in ionization energy increases.

Step-by-step solution

Understand Ionization Energies

Ionization energies are the energy required to remove electrons from an atom. The first, second, and third ionization energies correspond to the energy needed to remove the first, second, and third electrons, respectively. For Tl and Al, these values show how strongly each atom holds its electrons, which contributes to the stability of their ions.

Organize Data for Plotting

List the given ionization energies for thallium (Tl) and aluminum (Al): - Thallium (Tl): - First ionization energy (IE1): 589 kJ/mol - Second ionization energy (IE2): 1971 kJ/mol - Third ionization energy (IE3): 2878 kJ/mol - Aluminum (Al): - First ionization energy (IE1): 577.5 kJ/mol - Second ionization energy (IE2): 1817 kJ/mol - Third ionization energy (IE3): 2745 kJ/mol These values represent the energies needed to remove the successive electrons from each element.

Plot Ionization Energies

On the x-axis, plot the number of electrons removed (1, 2, 3). On the y-axis, plot the ionization energies (in kJ/mol) of Tl and Al. Each ionization energy corresponds to removing a subsequent electron: - For plot points of Tl, use: (1, 589), (2, 1971), (3, 2878) - For plot points of Al, use: (1, 577.5), (2, 1817), (3, 2745) Connect the points for each element to see the trend (usually, a line graph is most suitable).

Interpret the Plot and Trends

Generally, ionization energy increases as more electrons are removed because each subsequent electron is removed from a more positively charged ion. Comparing Tl and Al, notice that Tl's first ionization energy is slightly higher than Al's, suggesting it requires more energy to remove the first electron. However, Al shows a smaller jump in ionization energy from the first to the second and third electron removal, indicating its stability in the +3 oxidation state, in contrast to Tl which prefers the +1 state.

Key concepts

Ionization Trends

Ionization energy refers to the energy required to remove an electron from an atom or ion. It generally increases as electrons are removed. This increase occurs because, after removing an electron, the ion becomes more positively charged. This positive charge strengthens the attraction between the nucleus and the remaining electrons, thus, more energy is needed to overcome this force for each subsequent electron.

When plotting ionization energy against the number of electrons removed for any element, we typically see an upward trend. However, the rate of increase can vary. Elements with a full outer shell do not generally exhibit large increases since they are already stable and do not need to lose more electrons. Conversely, elements that have an incomplete valence shell may show dramatic increases, particularly from first to second ionization energies.

Thallium Ionization

Thallium's ionization energies are 589 kJ/mol (first), 1971 kJ/mol (second), and 2878 kJ/mol (third). These values reflect its preference for the +1 oxidation state.

Observing the increase from first to second ionization energy, there's a significant jump. This large increase suggests that thallium strongly prefers to lose only one electron, stabilizing in a +1 oxidation state. The enormous requirement for removing the second electron indicates that, once thallium has lost its first electron, it forms a more stable, less reactive ion.

The third ionization energy is even larger, reinforcing the idea that moving beyond the +1 state is energetically costly for thallium.

Aluminum Ionization

In contrast, aluminum's ionization energies are 577.5 kJ/mol (first), 1817 kJ/mol (second), and 2745 kJ/mol (third). Aluminum demonstrates a more uniform increase across the ionization energies.

The increase from the first to the second ionization energy is substantial but not as steep as thallium's, implying aluminum can relatively easily lose more than one electron. The third ionization energy indicates that aluminum readily achieves a +3 oxidation state, aligning with its stability in this form in chemical compounds.

This trend illustrates how aluminum, with its fewer outer-shell electrons compared to thallium, does not require as significant an energy increase to continue losing electrons.

Oxidation States

Oxidation states are indicative of the number of electrons an atom has lost, gained, or shared when bonding with other atoms. They play a crucial role in chemical reactions and are pivotal in determining an element's reactivity and stability in its ionic form.

Thallium often exists in the +1 oxidation state due to its high first ionization energy and dramatic increase to the second. This means it generally stabilizes after losing one electron, contributing to its use in certain compounds.

Aluminum, on the other hand, stabilizes in the +3 oxidation state. After losing three electrons, it achieves a noble-gas-like configuration, making it less reactive and more stable in this form. The stability in these oxidation states is influenced by their respective ionization energies, as shown in the trends of their ionization.

Periodic Table Trends

Ionization energy trends across the periodic table are critical for understanding the behavior of elements. As you move across a period from left to right, ionization energy generally increases because electrons are added to the same energy level while the nucleus simultaneously gains more protons. This increased nuclear charge attracts the electrons more strongly.

Moving down a group, ionization energy generally decreases. Additional electron shells are added, which increases the distance between the nucleus and the outermost electrons, reducing the attractive force and making electrons easier to remove.

Thallium and aluminum demonstrate these principles. Thallium, being lower in the group, shows a higher initial and subsequent ionization energy compared to aluminum. Although aluminum's energies rise steadily, they reflect the characteristics of an element that's higher on the periodic table, where less energy is typically required for electron removal.