Question

Explain why the radius of a chloride ion \((0.181 \mathrm{nm})\) is about twice that of a chlorine atom \((0.099 \mathrm{nm})\).

Short answer

The chloride ion is larger than the chlorine atom because gaining an electron increases electron repulsion and the size of the electron cloud.

Step-by-step solution

Understanding Ion and Atom

An atom is the smallest unit of an element, and ions are atoms or molecules that have lost or gained one or more electrons, which makes them charged. A chloride ion (Cl⁻) is formed when a chlorine atom (Cl) gains an electron.

Visualizing Electron Gain

Adding an electron to a chlorine atom to form a chloride ion increases the electron-electron repulsion within the atom. This repulsion happens because all electrons have the same negative charge and repel each other.

Influence on Atomic Size

The additional electron increases the size of the electron cloud around the nucleus due to increased repulsion, which makes the size of the chloride ion larger compared to the neutral chlorine atom.

Comparison of Radii

The increase in size from the additional electron means the radius of the chloride ion (0.181 nm) is about twice that of the chlorine atom (0.099 nm), since the added electron effectively increases the distance from the nucleus to the outermost electron cloud.

Key concepts

Chlorine Atom

A chlorine atom is a fundamental entity in chemistry. It is an atom of the chemical element chlorine, which has the symbol Cl and an atomic number of 17. This means a chlorine atom has 17 protons in its nucleus and typically the same number of electrons orbiting this nucleus, creating an electrically neutral state. Chlorine atoms exist as part of compounds in nature and are rarely found alone due to their high reactivity. Understanding the structure of a chlorine atom is essential in grasping how it interacts to form compounds like chloride ions.

Chloride Ion

A chloride ion is simply a chlorine atom that has gained an extra electron, thereby acquiring a negative charge, denoted as Cl⁻. This process transforms a neutral, highly reactive atom into a stable ion. The addition of an electron to a chlorine atom fills its outer electron shell, achieving what is known as the octet rule—a state of eight electrons in its valence shell, which is particularly stable. Chloride ions are ubiquitous in nature, found in common compounds like table salt (NaCl) and are crucial for processes such as electrical signaling in cells.

Electron-Electron Repulsion

Electron-electron repulsion is a significant concept in understanding atomic structure. Electrons, which are negatively charged, naturally repel one another. This repulsion plays a critical role when an electron is added to an atom, as is the case with the formation of a chloride ion.

• The added electron increases repulsive forces between the electrons.
• It forces them to spread further apart.

This spreading out of electrons affects their overall arrangement and leads to an expansion of the electron cloud around the nucleus. The increased repulsion resulting from added electrons directly impacts the atomic radius, making it noticeably larger.

Atomic Radius

The atomic radius is defined as the distance from the nucleus of an atom to the outer boundary of the electron cloud. In simple terms, it indicates how big an atom or ion is. Several factors can influence the atomic radius:

• Number of electrons.
• Proximity of these electrons to the nucleus.
• Electron-electron interactions.

When a chlorine atom turns into a chloride ion by gaining an electron, the additional electron contributes to a larger atomic radius due to increased electron-electron repulsion. As a result, the chloride ion's atomic radius of 0.181 nm is nearly twice that of the chlorine atom's 0.099 nm, as the electron cloud extends further from the nucleus to accommodate the extra electron.