---
title: "The Periodic Table"
description: "Describe the organisation of the periodic table into periods and groups, explain the contribution of Mendeleev, and use the table to identify metals, non-metals, and predict patterns in reactivity"
canonical: https://lightmysky.com/learn/science/the-periodic-table-mt_wfEfQuHOG-
source: https://lightmysky.com/learn/science/the-periodic-table-mt_wfEfQuHOG-.md
retrieved: 2026-10-19
---

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# The Periodic Table

Describe the organisation of the periodic table into periods and groups, explain the contribution of Mendeleev, and use the table to identify metals, non-metals, and predict patterns in reactivity

Subject: Science · Area: Matter & Materials · Ages 11 to 12
Page: https://lightmysky.com/learn/science/the-periodic-table-mt_wfEfQuHOG-

## Ready when they can

- Explains why the periodic table is arranged into periods (rows) and groups (columns)
- States that elements in the same group have similar chemical properties
- Locates metals, non-metals, and metalloids in the periodic table
- Explains how Mendeleev ordered elements by atomic weight and predicted missing elements

## Lesson: The periodic table: periods, groups, and Mendeleev

You already know that everything is built from atoms and elements. Scientists took every known element and put it on one chart called the periodic table, so you can guess how a new element might behave just from where it sits. The chart has rows called periods and columns called groups.

*(drawing: This simple grid has 7 rows for periods and 10 columns for groups. The real table has more columns, but rows are still periods and columns are still groups.)*

**Example.** In 1869, a chemist named Dmitri Mendeleev lined up all the known elements in order of their atomic weight. A pattern of properties kept repeating. When an element seemed to be missing from the pattern, he left a blank space instead of forcing a bad fit, and he predicted what that missing element would be like. Years later, chemists found those exact elements, and his predictions matched.

*(drawing: Lithium, sodium, potassium, and rubidium all sit in the same column. Because they share a group, they all react strongly with water in the same way.)*

**Tip.** Use where an element sits to guess what it is. Most of the table, the left and the middle, is metal. Non-metals crowd the top right corner. A jagged staircase line runs between them, and elements touching that line are metalloids, part metal and part non-metal.

**Recap.** Periods are rows, groups are columns, elements in the same group behave alike, and that pattern is exactly what let Mendeleev predict elements before anyone found them.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Atoms, Elements & Compounds](https://lightmysky.com/learn/science/atoms-elements-and-compounds-mt_Z_Wu_77ybI)

## Opens up

- [Electron Shells and the Shape of the Periodic Table](https://lightmysky.com/learn/science/electron-shells-and-the-shape-of-the-periodic-table-mt__Sdcw4RnZF)
- [Naming Ionic and Simple Molecular Compounds](https://lightmysky.com/learn/science/naming-ionic-and-simple-molecular-compounds-mt_GJ267pzxCI)
- [Metals vs Non-Metals](https://lightmysky.com/learn/science/metals-vs-non-metals-mt_Sc_SorJhXW)
- [Inside the Atom: Protons, Neutrons and Electrons](https://lightmysky.com/learn/science/inside-the-atom-protons-neutrons-and-electrons-mt_WqDXAr2IkA)