Question

In each of the following pairs, which has the larger radius? (a) Al atom or Al ion (b) \(\mathrm{Pb}\) atom or \(\mathrm{Pb}\) ion (c) Se atom or Se ion (d) \(\mathrm{N}\) atom or \(\mathrm{N}\) ion

Short answer

Larger radii: (a) Al atom, (b) Pb atom, (c) Se ion, (d) N ion.

Step-by-step solution

Analyzing Aluminum (Al) Atom and Ion

An Aluminum (Al) ion is formed when the atom loses three electrons to become Al³⁺. This loss reduces the electron cloud size significantly since there are fewer electrons repelling each other. Therefore, the radius of an Al ion (Al³⁺) is smaller than the radius of an Al atom. Answer: Al atom has the larger radius.

Analyzing Lead (Pb) Atom and Ion

When a Lead (Pb) atom forms an ion by losing electrons, it typically forms a Pb²⁺ ion. Similar to aluminum, the loss of electrons in lead ions results in a smaller electron cloud and reduced electron-electron repulsion. Thus, the ionic radius of Pb²⁺ is smaller than the atomic radius of Pb. Answer: Pb atom has the larger radius.

Analyzing Selenium (Se) Atom and Ion

A Selenium (Se) atom usually forms Se²⁻ by gaining two electrons. The addition of electrons increases electron-electron repulsion and results in the enlargement of the electron cloud. Hence, the ionic radius of Se²⁻ is larger than the atomic radius of Se. Answer: Se ion has the larger radius.

Analyzing Nitrogen (N) Atom and Ion

Nitrogen (N) can gain three electrons to form N³⁻. This gain increases the electron cloud due to increased electron-electron repulsion, thereby enlarging the ion's size. Consequently, the ionic radius of N³⁻ is greater than the atomic radius of N. Answer: N ion has the larger radius.

Key concepts

Electron Configuration

Electron configuration describes how electrons are arranged around an atom's nucleus. Understanding an atom's electron configuration is essential for determining its chemical properties, including an element's reactivity and bond-forming abilities.

Electrons are organized into shells, subshells, and orbitals around the nucleus. A shell consists of orbitals, and each orbital can hold a specific number of electrons:

• The first shell (closest to the nucleus) can hold up to 2 electrons.
• The second shell can accommodate up to 8 electrons.
• The third shell can hold up to 18 electrons, and so on.

Each element has a unique electron configuration that can be noticed using the periodic table. Usually, the electron configuration of an element predicts how it interacts with other elements. For example, when an atom loses electrons, it becomes a positively charged ion (cation) with fewer electrons than protons. Conversely, when an atom gains electrons, it becomes negatively charged (anion), having more electrons than protons. Thus, alterations to electron configurations during ion formation are crucial for determining ionic radii and chemical behavior.

Atomic Structure

The atomic structure is the foundation of an atom, comprising three primary subatomic particles: protons, neutrons, and electrons. Each of these particles plays a unique role in an atom's characteristics:

• Protons, with a positive charge, reside in the nucleus and determine the atom's identity identified by the atomic number.
• Neutrons, which are neutral, also reside in the nucleus, contributing to the atom's mass but not its charge.
• Electrons, with a negative charge, orbit the nucleus within electron shells.

The balance between protons and electrons determines the atom's overall charge.

Understanding atomic structure helps explain why atoms form ions. When neutral atoms undergo ionization, they either gain or lose electrons, impacting the atomic size and structure. For instance, losing electrons will usually result in a positive ion, and the electron cloud shrinks without the repulsive forces of the missing electrons. Gains result in negative ions, enlarging the electron cloud due to increased repulsion. This underlying structure ultimately dictates the chemical properties and the atomic behavior of substances.

Ionization and Electron Affinity

Ionization energy and electron affinity are critical concepts related to the formation of ions. These terms are placed within the broader framework of atomic interactions and define how atoms transform into ions by losing or gaining electrons respectively.

• Ionization Energy: This is the energy required to remove an electron from an atom. It indicates how strongly an atom holds onto its electrons. A high ionization energy means an electron is tightly bound to the nucleus, suggesting that it will require more energy to remove it.
• Electron Affinity: This refers to the energy change when an electron is added to a neutral atom. Electron affinity measures the tendency of an atom to gain an additional electron. A more negative electron affinity implies a greater tendency to accept an electron.

Both ionization energy and electron affinity directly affect the formation and stability of ions. Atoms with low ionization energy, like metals, lose electrons easily to form cations. On the other hand, nonmetals with highly negative electron affinity readily gain electrons to form anions. These properties not only influence the formation of ions but also determine the ionic and atomic radius sizes, further emphasizing their significance in the study of chemical bonding and reactions.