--- 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 get used." 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: 2026-09-12 --- > **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 get used. 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 each atom grows, so outer electrons sit further out behind more shielding. They leave more easily, ionisation energy falls, and the metals attack water more fiercely. Magnesium reacts slowly, while calcium, strontium and barium fizz faster and faster. The pattern is: metal plus water gives the hydroxide plus hydrogen, for example Ca plus 2H2O gives Ca(OH)2 plus H2. Their oxides do the same job: CaO plus H2O gives Ca(OH)2. Two solubility trends run opposite down the group. The hydroxides grow more soluble going down, so barium hydroxide dissolves far better than magnesium hydroxide. The sulfates run the other way and grow less soluble, so barium sulfate barely dissolves at all. **Example.** Doctors and pharmacists spend both trends. Barium sulfate is so insoluble that a swallowed barium meal passes straight through, letting X-rays see the gut even though free barium ions are toxic. Magnesium hydroxide is soluble enough to neutralise excess stomach acid, which is why it stars in indigestion remedies. **Tip.** Always explain the reactivity trend with ionisation energy, shielding and distance, not size alone. Bigger atoms react faster only because their outer electrons are held more loosely. **Recap.** Reactivity and hydroxide solubility rise down the group while sulfate solubility falls, and medicine uses both. ## 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) - [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)