Question

What is the order of successive ionisation enthalpies? (a) \(I E_{\mathrm{III}}>I E_{\mathrm{II}}>I E_{1}\) (b) \(I E_{1}>I E_{\mathrm{II}}>I E_{\mathrm{II}}\) (c) \(\mathrm{IE}_{\mathrm{II}}>I E_{\mathrm{1}}>I E_{\mathrm{m}}\) (d) \(I E_{\mathrm{III}}>I E_{\mathrm{I}}>I E_{\mathrm{II}}\)

Short answer

The correct order is (a) IE3 > IE2 > IE1.

Step-by-step solution

Understanding Ionization Energy

Ionization energy (IE) is the energy required to remove an electron from a gaseous atom or ion. The first ionization energy, IE1, is the energy to remove the first electron. Successive ionization energies, such as IE2, IE3, etc., are energies needed to remove the second electron, third electron, and so on. Each successive ionization energy is larger than the one before because the electrons are being removed from an increasingly positive ion, thus feeling a stronger attraction to the nucleus.

Analyzing the Options

Based on the concept that each successive removal of an electron requires more energy due to the increasing positive charge of the ion, we can determine the correct order. After removing one electron (IE1), the ion becomes more positively charged and it takes more energy to remove the second electron (IE2). This pattern continues, thus IE3 is greater than IE2 and so on.

Identifying the Correct Order

With the knowledge from the previous steps, we can evaluate the given options. The correct order is that each successive ionization energy must be greater than the previous one because it is more difficult to remove an electron from an increasingly positive ion.

Eliminating Incorrect Options

Option (b) is incorrect since it states IE1 twice. Option (d) is incorrect because IE1 should be the smallest. By comparing the remaining options, we conclude that option (a) correctly represents the order: IE3 > IE2 > IE1.

Key concepts

Ionization Energy

Ionization energy (IE) is a fundamental concept in chemistry that deals with the amount of energy needed to remove an electron from an isolated atom or molecule in the gaseous state. The first ionization energy, IE1, is the energy required to remove the outermost, or least tightly bound, electron from a neutral atom. Atoms hold their electrons with varying degrees of strength, generally depending on the distance from the nucleus and the overall charge of the atom. This concept is crucial for understanding the reactivity of elements and plays a significant role in the formation of ionic bonds.

While it may seem like a straightforward process, the removal of an electron is influenced by several factors, including atomic size, nuclear charge, and the electron configuration of the atom. Typically, elements on the right side of the periodic table have higher ionization energies because their electrons are closer to the nucleus and more strongly attracted to it. Hence, understanding this concept not only provides insight into elemental properties but also into the underlying principles of atomic structure and periodicity.

Successive Ionization Energies

Successive ionization energies refer to the energy required to remove electrons beyond the first. After the removal of the first electron, resulting in IE1, the subsequent electrons require progressively higher amounts of energy to be removed, known as IE2, IE3, and so on. This is due to the fact that after each electron is removed, the positive charge of the ion increases, which in turn causes the remaining electrons to experience a greater electrostatic pull from the nucleus.

It's essential to pay close attention to these energies as they can reveal significant information about an element's electron configuration. Significant increases in successive ionization energies typically indicate the removal of an electron from a new, closer energy level to the nucleus, representing a major shift such as moving from a p-orbital to a s-orbital electron. These details are instrumental when deducing an element's position in the periodic table and are often used to explain the chemical behavior of atoms during the bonding process.

Removal of Electrons

The removal of electrons from an atom is a process that requires external energy and is governed by specific rules based on quantum mechanics and electrostatic forces. Each electron removed from an atom makes the subsequent removal more challenging because each electron carries a negative charge which is balanced by the positive charge of the protons in the nucleus. As the balance shifts due to electron removal, remaining electrons are more strongly attracted to the now more positively charged nucleus.

The process of electron removal is not only theoretical but has practical applications in fields such as materials science, where the ionization energies correlate with electrical conductivity and in astrophysics, where the ionization energy of elements in stars can influence the star's spectrum. In the context of a chemical reaction, the ease of electron removal plays a significant role in determining the reactivity of an element, with low ionization energies often leading to high reactivity in elements such as alkali metals.