Helium (He): Chemical Properties & Reactions (Exam Guide)

Chemical Properties Overview

Reactivity

Helium (He), a member of Group 18 (Noble Gases), possesses a highly stable electron configuration of 1s². This completely filled valence shell renders Helium extremely unreactive under standard conditions. It exhibits minimal to no tendency to gain, lose, or share electrons, thus forming very few, if any, stable chemical compounds.

Electronegativity

Due to its chemical inertness and lack of tendency to form covalent bonds, electronegativity values are generally not defined or assigned to Helium in standard scales such as the Pauling scale. Its filled valence shell signifies no chemical drive to attract electrons in a bonding scenario.

General Reactivity

Helium is considered chemically inert. It does not participate in typical chemical reactions such as oxidation, reduction, or acid-base reactions under normal laboratory conditions. This inertness is a defining characteristic of noble gases.

Action of Air and Oxygen

Helium does not react with air or oxygen. It is intrinsically non-combustible and does not support combustion. No chemical transformation occurs even at elevated temperatures or pressures relevant to high school chemistry.

• Reaction: $\text{He(g) + O}_2\text{(g) } \rightarrow \text{No Reaction}$

Action of Water and Steam

Helium is insoluble in water and exhibits no chemical reactivity towards water or steam. Its inert nature persists across various temperature and pressure conditions.

• Reaction: $\text{He(g) + H}_2\text{O(l/g) } \rightarrow \text{No Reaction}$

Action of Acids and Bases

Helium is chemically unreactive towards both acids and bases. It does not react with dilute or concentrated mineral acids, nor with strong or weak alkalis.

• Reaction with Acids: $\text{He(g) + Acid } \rightarrow \text{No Reaction}$
• Reaction with Bases: $\text{He(g) + Base } \rightarrow \text{No Reaction}$

Key Laboratory Test/Identification Reactions

Given Helium’s extreme chemical inertness, there are no conventional chemical wet tests (e.g., precipitation, colour change, gas evolution from reaction) available for its identification in a high school laboratory. Identification relies on its distinct physical properties or advanced spectroscopic methods:

1. Inertness: As a gas, Helium can be identified by its inability to burn or support combustion. If a flame is introduced, the gas will not ignite, nor will it sustain the flame. This distinguishes it from flammable gases (e.g., hydrogen) and reactive gases (e.g., oxygen).
2. Low Density: Helium is significantly less dense than air. This property is evident in its ability to fill balloons that float. A simple density comparison can indicate its presence.
3. Atomic Emission Spectroscopy: The most definitive identification method is through its unique atomic emission spectrum. When Helium gas is excited by an electric discharge, it emits light at characteristic wavelengths, producing a distinct spectral signature. This method, however, is typically beyond routine high school practical work.