⏰ when
When was atomic number first used to order the periodic table?
ChemistryPeriodic Table
Quick Answer
Atomic number began replacing atomic mass as the key ordering principle in 1913.
The Full Story
The modern principle of ordering the periodic table by atomic number was established in 1913 by Henry Moseley. Moseley’s X-ray measurements showed that each element has a unique nuclear charge, which corresponds to its atomic number. This solved problems in earlier tables that were arranged mainly by atomic mass and sometimes had awkward exceptions. Moseley’s work gave the periodic table its modern scientific foundation.
Key Facts
1.Established in 1913
2.Work by Henry Moseley
3.Based on atomic number, not mass
YouTube Angle
Suggested video title for this topic:
"The hidden number that fixed the periodic table"