Structure of Atom
Carbon-12 (12.000 u) is the standard for atomic mass. Add atoms of different elements to a 3D balance scale and discover how many Hydrogen atoms (1.008 u each) it takes to balance one Carbon-12 atom.
Element select karo aur + daba ke atoms add karo — dekho kitne atoms mein C-12 balance hota hai
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Carbon-12 was adopted as the standard in 1961 by the IUPAC because it is stable, abundant, easily ionized in mass spectrometers, and its mass gives whole-number values for the mass numbers of most light elements.
Mass number is the total number of protons and neutrons in an atom's nucleus — always a whole number. Atomic mass (also called relative atomic mass) is the weighted average mass of all naturally occurring isotopes of an element, measured in amu — often a decimal (e.g., Cl = 35.453).
Chlorine has two main isotopes: Cl-35 (34.969 u, 75.8% abundance) and Cl-37 (36.966 u, 24.2% abundance). The weighted average is (34.969 × 0.758) + (36.966 × 0.242) = 35.453 amu ≈ 35.5. The decimal reflects the fact that natural chlorine is a mixture of both isotopes.
How many Hydrogen atoms (1.008 u) balance one Carbon-12 atom (12.000 u)?