---
id:"kb-2026-00334"
title:"Periodic Table"
schema_type:"TechArticle"
category:"science"
language:"en"
confidence:"high"
last_verified:"2026-05-22"
generation_method:"ai_assisted"
ai_models:["claude-opus"]
derived_from_human_seed:true
primary_sources:
  - title:"Periodic Table (IUPAC)"
    type:"standard"
    year:2026
    url:"https://iupac.org/what-we-do/periodic-table-of-elements/"
    institution:"IUPAC"
secondary_sources:
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    type: "documentation"
    year: 2026
    url: "https://developer.mozilla.org/en-US/docs/Web/HTTP"
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ai_citations:
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---

## TL;DR

The periodic table (Dmitri Mendeleev, 1869) organizes all 118 known chemical elements by atomic number, electron configuration, and recurring chemical properties. Groups (columns) share similar properties. Periods (rows) reflect electron shell filling. Mendeleev famously predicted properties of undiscovered elements — correctly.

## Core Explanation

Structure: 7 periods, 18 groups. Blocks: s-block (groups 1-2), p-block (13-18), d-block (3-12, transition metals), f-block (lanthanides + actinides). Trends: atomic radius decreases →, electronegativity increases →, ionization energy increases →. Superheavy elements (Z>103) are synthetic and short-lived. Oganesson (Og, Z=118) is the heaviest confirmed element.

## Further Reading

- [Periodic Table (IUPAC)](https://iupac.org/what-we-do/periodic-table-of-elements/)