← 🧪 Chemistry · usually met in Std 8-12
All the known elements arranged so that the pattern in their behaviour becomes a pattern on a page — and the gaps in it predicted elements nobody had found.
Mendeleev laid the elements out by increasing mass in 1869 and noticed their properties repeated at intervals. Rather than force the awkward ones into line, he left gaps where he thought an undiscovered element belonged, and predicted what each would be like. When those elements turned up and matched, the table stopped being a filing system and became a law. Today the elements are ordered by atomic number — the proton count — which removed the last few anomalies.
Reading it is a skill worth having. A column is a group, and a group shares a chemical character because its members have the same number of outer electrons. A row is a period. The far left is the reactive metals, the far right the noble gases that react with almost nothing, and the useful metals of everyday life sit in the block in the middle.
Want to see it moving? Search YouTube for “The periodic table” ↗ — we send you to the search rather than to one video, because a link to one video eventually rots.
This entry was written for Star Student in our own words — it is a summary, not a source. Here is where the people who actually hold these facts keep them. Go and check.
Your own textbook ↗Balbharati publishes the textbooks free to read online. Your chapter is the thing to check first — an encyclopedia is a summary, and the syllabus is the syllabus.Last gone through: 1 October 2026 · How these entries are written
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