Question

The metallic lusture exhibited by sodium is explained by: (a) Diffusion of sodium ions (b) Oscillation of loose electrons (c) Excitation of free electrons (d) Existence of body centred cubic lattice.

Short answer

The metallic lustre of sodium is explained by the oscillation of loose electrons (option b).

Step-by-step solution

Understand Metallic Luster

Metallic luster is a property of metals due to the reflection of light by the surface electrons. To solve the problem, we need to determine which option explains this reflectivity in sodium.

Analyze Each Option

Review the provided options: (a) Diffusion of sodium ions - This refers to the movement of ions, not relevant to shine. (b) Oscillation of loose electrons - Electrons on a metal surface can oscillate, contributing to shine. (c) Excitation of free electrons - Excited electrons mean energy absorption, typically not the cause of lustre. (d) Existence of body-centered cubic lattice - Refers to crystal structure, not directly about electron behavior related to lustre.

Identify Correct Explanation

Reflectivity in metals, including sodium, is largely due to the behavior of loose or free electrons that oscillate and reflect light. Therefore, the explanation of sodium's metallic luster is best described by option (b).

Key concepts

Sodium

Sodium is a highly reactive alkali metal prominently found in the periodic table's first group. Its properties make it an essential element in various chemical reactions and industrial applications. One of sodium's unique characteristics is its metallic luster.

This shimmer is typical of metals and results from how sodium interacts with light. At the atomic level, sodium has a single electron in its outermost shell, which plays a crucial role in its reactivity and metallic sheen.

When compared to other metals, sodium is soft, malleable, and less dense. These physical attributes, alongside its shiny appearance, have led to its valued presence in both educational demonstrations and practical applications.

Free Electrons

Free electrons are a fundamental concept in understanding the shiny appearance of metals like sodium. These electrons are not tightly bound to any specific atom within the metal structure, allowing them to move freely across the surface.

• Mobility allows them to interact readily with incoming light.
• When light hits the surface of a metal, these free electrons oscillate and reflect light back, resulting in the luster we observe.

This interaction does not consume energy permanently, as the electrons oscillate back and forth, re-emitting the light. Hence, the presence of free electrons is integral to the metallic luster found in sodium and other metals.

This concept is crucial not just in explaining metallic appearance, but also in understanding other properties such as electrical and thermal conductivity.

Reflectivity

Reflectivity is the ability of a surface, like that of sodium, to bounce back light waves. Metals are particularly good reflectors of light due to their free electrons. When light strikes the surface of a metal:

• The free electrons oscillate in response, mirroring the light waves back, which gives a shiny, lustrous appearance.
• This process is constant, meaning metals maintain their shine unless physically altered or tarnished.

Metal reflectivity is utilized in various applications, from decorative items to electrical components and beyond.

While other materials can also reflect light, metals like sodium do so exceptionally well, explaining why they standout with their metallic luster.

Body-Centered Cubic Lattice

The body-centered cubic (BCC) lattice is a type of crystal structure seen in many metals, including sodium. In a BCC arrangement, the basic structure consists of atoms positioned at the eight corners and a single atom at the center of the cube.

This arrangement accounts for some of the distinctive properties of metals, including density and malleability. However, while the BCC structure is vital to understanding physical properties, it doesn't directly account for the metallic luster.

Instead, metallic luster primarily results from the free electrons moving across the metal surface, as seen with sodium. Yet, the BCC structure would contribute to how closely packed and uniformly free electrons can move, indirectly influencing how efficiently light is reflected. Therefore, the BCC structure subtly supports the overall metallic nature but isn't the direct cause of reflectivity and luster.