Tungsten (W) Study Guide - Properties, Reactions & Uses

Introduction: The Significance of Tungsten

Tungsten (W), derived from the Swedish words “tung sten” meaning “heavy stone,” is a remarkable transition metal known for its exceptional properties. It boasts the highest melting point of all known metals, superior tensile strength at high temperatures, and excellent corrosion resistance. These characteristics make it indispensable in numerous high-performance applications, from incandescent light filaments to high-speed cutting tools and specialized alloys.

CBSE/JEE Quick Revision Notes

Symbol: W
Atomic Number: 74
Atomic Mass: 183.84 u
Group: 6
Period: 6
Block: d-block (Transition Metal)
Nature: Hard, brittle, silvery-white metal
Melting Point: 3422 °C (Highest of all metals)
Boiling Point: 5930 °C
Density: 19.25 g/cm³ (Very high)
Common Oxidation States: +2, +3, +4, +5, +6 (Most stable and common is +6)
Crystal Structure: Body-Centered Cubic (BCC)

Electron Configuration & Bonding Behavior

Electron Configuration

Tungsten’s electron configuration is: [Xe] 4f^14 5d^4 6s^2

Bonding Behavior

Tungsten exhibits variable oxidation states, characteristic of transition metals, with +6 being the most common and stable. Its high oxidation states result from the participation of both 5d and 6s electrons in bonding. Tungsten compounds, particularly those in higher oxidation states, often display significant covalent character. It forms stable oxides (like WO₃), halides (like WF₆), and tungstates (salts of tungstic acid, H₂WO₄). The strength of its metallic bonds contributes to its extraordinarily high melting point.

Crucial Chemical Reactions

Tungsten is relatively unreactive at room temperature but reacts at elevated temperatures.

Reaction with Oxygen

Tungsten burns in oxygen at high temperatures to form tungsten(VI) oxide (tungsten trioxide). 2W(s) + 3O₂(g) --(heat)--> 2WO₃(s)

Reaction with Halogens

Tungsten reacts with halogens to form various tungsten halides. For example, with fluorine, it forms tungsten(VI) fluoride, a volatile compound. W(s) + 3F₂(g) --(heat)--> WF₆(g) With chlorine, it can form tungsten(VI) chloride: 2W(s) + 6Cl₂(g) --(heat)--> 2WCl₆(s)

Reaction with Acids

Tungsten is generally resistant to attack by most acids at room temperature.

Non-oxidizing acids (e.g., HCl, dilute H₂SO₄): Tungsten is largely unreactive.
Strong oxidizing acids (e.g., hot concentrated HNO₃): Tungsten reacts to form tungstic acid (H₂WO₄), which is insoluble. W(s) + 6HNO₃(conc) --(heat)--> H₂WO₄(s) + 6NO₂(g) + 2H₂O(l)
Mixture of Hydrofluoric and Nitric Acid (HF/HNO₃): This mixture can dissolve tungsten, forming hexafluorotungstic acid. W(s) + 10HF(aq) + 2HNO₃(aq) --> H₂[WF₆](aq) + 2NO(g) + 6H₂O(l)

Reaction with Bases

Tungsten is generally resistant to alkali solutions, but it can slowly dissolve in molten alkalis to form tungstates. WO₃(s) + 2NaOH(l) --(heat)--> Na₂WO₄(l) + H₂O(g)

Industrial and Biological Importance

Industrial Importance

Tungsten’s unique properties make it critical for numerous industrial applications:

Filaments: Its high melting point and strength make it ideal for incandescent light bulb filaments, vacuum tube filaments, and X-ray tube targets.
Alloys: Tungsten is extensively used to make hard, heat-resistant alloys.
- High-Speed Steel: Improves hardness, strength, and wear resistance, maintaining these properties at high temperatures (e.g., for cutting tools).
- Superalloys: Used in jet engine components, rocket nozzles, and other high-temperature applications.
Tungsten Carbide (WC): An exceptionally hard material, often mixed with cobalt (cemented carbide), used for cutting tools (drills, milling cutters), abrasives, armor-piercing ammunition, and mining equipment.
Electrodes: Used in TIG (Tungsten Inert Gas) welding due to its high melting point and electrical conductivity.
Electrical Contacts: Used in switches and circuit breakers.
Counterweights and Ballasts: Its high density makes it suitable for counterweights in aircraft, golf clubs, and radiation shielding.
Chemical Industry: Tungsten oxides and sulfides serve as catalysts in various chemical reactions.

Biological Importance

Tungsten is an essential trace element for certain microorganisms (some bacteria and archaea) where it functions as a cofactor in specific enzymes, particularly oxidoreductases (e.g., aldehyde ferredoxin oxidoreductase). However, it is not considered an essential element for humans or higher animals. While generally low in toxicity, high concentrations can interfere with molybdenum metabolism due to their chemical similarities.