Atoms are incredibly tiny, so weighing them in grams or kilograms is impractical. Instead, scientists use a relative scale called the Atomic Mass Unit (amu), which is now officially written simply as 'u' (unified mass).
Symbol: amu (older) or u (modern 'unified mass').
Definition: 1/12th the mass of a Carbon-12 atom.
Standard Reference: Carbon-12 isotope.
1 amu = 1.66 × 10⁻²⁴ g.
Mass of a proton or neutron ≈ 1 amu.
One Atomic Mass Unit (1 amu) is defined as a mass exactly equal to one-twelfth (1/12th) of the mass of one Carbon-12 atom.
Why Carbon-12? Because it is abundant, stable, and has exactly 6 protons and 6 neutrons. It was chosen as the international standard reference in 1961.
Think of a Carbon-12 atom as a pie cut into exactly 12 equal slices.
If you convert 1 amu into standard metric units, the number is unimaginably small: 1 amu = 1.660539 × 10⁻²⁴ grams
One atomic mass unit (amu or u) is defined as a mass exactly equal to 1/12th of the mass of one Carbon-12 atom.
The Carbon-12 isotope is used as the international standard reference for atomic mass.
Which Metal is Used for Galvanising Iron?
Zinc (Zn) is used for galvanising iron. Galvanisation coats iron with zinc to prevent rusting. Methods: hot-dip and electrogalvanising. Zinc is a sacrificial anode.
Methanoic Acid Formula — HCOOH Structure, Name and Properties
Methanoic acid (formic acid) formula is HCOOH or HCO₂H. It is the simplest carboxylic acid. Learn its structure, properties, occurrence, and uses with FAQs.
How to Liquefy Atmospheric Gas?
Learn the method to liquefy atmospheric gas. Understand how applying high pressure and lowering the temperature changes gases into liquids (Class 9 Chemistry).
Colour of Methyl Orange in Acid and Base
Learn the colour of methyl orange in acidic and basic solutions. Understand why it changes from red to yellow and its use in titrations.
Milk Is an Example of Which Type of Matter?
Milk is a colloid — specifically an emulsion. It is a heterogeneous mixture of fat droplets dispersed in water. Learn why milk is a colloid with FAQs.
Turn this guide into revision flashcards, a practice exam, or an AI-generated podcast — free, no signup required.