--- title: "Group 2: Reactivity and Solubility Trends" description: "Down group 2 the outer electrons come away more easily, so reactions with water get more vigorous. Hydroxide solubility rises down the group while sulfate solubility falls, and both trends have uses." canonical: https://lightmysky.com/learn/science/group-2-reactivity-and-solubility-trends-mt_Ch8FEkh-dV source: https://lightmysky.com/learn/science/group-2-reactivity-and-solubility-trends-mt_Ch8FEkh-dV.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Group 2: Reactivity and Solubility Trends Down group 2 the outer electrons come away more easily, so reactions with water get more vigorous. Hydroxide solubility rises down the group while sulfate solubility falls, and both trends have uses. Subject: Science · Area: Chemistry · Ages 16 to 17 Page: https://lightmysky.com/learn/science/group-2-reactivity-and-solubility-trends-mt_Ch8FEkh-dV ## Ready when they can - Explains the reactivity trend down the group in terms of ionisation energy - Writes equations for group 2 metals and their oxides reacting with water - States the opposite solubility trends of the hydroxides and of the sulfates - Explains a use such as barium sulfate in medical imaging or magnesium hydroxide in indigestion remedies from those trends ## Lesson: Down the alkaline earths Down Group 2, atoms have more shells. The outer electrons are farther from the nucleus and more shielded. Ionisation energy falls, so the metals lose electrons more easily. Reaction with water becomes more vigorous from magnesium to barium. A metal makes a hydroxide and hydrogen: Ca + 2H2O -> Ca(OH)2 + H2. Magnesium reacts only slowly with cold water, but with steam it gives magnesium oxide and hydrogen: Mg + H2O -> MgO + H2. *(drawing: The outer electrons are easier to remove lower down the group.)* The solubility patterns go in opposite directions. Group 2 hydroxides become more soluble down the group. Group 2 sulfates become less soluble, so barium sulfate dissolves very little. **Example.** A group 2 oxide reacts with water to make the hydroxide: CaO + H2O -> Ca(OH)2. Barium sulfate is used in gut scans because very little dissolves, so most passes through. Magnesium hydroxide dissolves enough to react with excess stomach acid. Use distance, shielding and ionisation energy to explain reactivity. Do not use atom size alone. More distance and shielding mean a weaker pull on the outer electrons. **Recap.** Reactivity and hydroxide solubility rise down Group 2, while sulfate solubility falls. These patterns explain the water reactions and the medical uses. *Original chemistry lesson and assessment text authored for os-taxonomy.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Period 3 Oxides and the Acid-Base Divide](https://lightmysky.com/learn/science/period-3-oxides-and-the-acid-base-divide-mt_3kC5hTavIQ) ## Optional connections - [Group 1, Group 7 and Group 0: Trends You Can Predict](https://lightmysky.com/learn/science/group-1-group-7-and-group-0-trends-you-can-predict-mt_cy1OrVAjIo) ## Opens up - [Group 7: Oxidising Power, Displacement and Halide Tests](https://lightmysky.com/learn/science/group-7-oxidising-power-displacement-and-halide-tests-mt_li7olQ3dM9)