--- title: "Group 1, Group 7 and Group 0: Trends You Can Predict" description: "Use outer-shell electrons to predict how alkali metals, halogens and noble gases behave, including why group 1 gets more reactive down the group while group 7 gets less." canonical: https://lightmysky.com/learn/science/group-1-group-7-and-group-0-trends-you-can-predict-mt_cy1OrVAjIo source: https://lightmysky.com/learn/science/group-1-group-7-and-group-0-trends-you-can-predict-mt_cy1OrVAjIo.md retrieved: 2026-09-02 --- > **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 1, Group 7 and Group 0: Trends You Can Predict Use outer-shell electrons to predict how alkali metals, halogens and noble gases behave, including why group 1 gets more reactive down the group while group 7 gets less. Subject: Science · Area: Matter & Materials · Ages 14 to 16 Page: https://lightmysky.com/learn/science/group-1-group-7-and-group-0-trends-you-can-predict-mt_cy1OrVAjIo ## Ready when they can - Predicts the products when a named group 1 metal meets water and writes the equation - Explains the reactivity trend down group 1 using distance from the nucleus and inner-shell shielding - Explains why the trend in group 7 runs the other way - Predicts whether one halogen will displace another from a solution of its salt ## Lesson: Groups 1, 7 and 0: trends you can predict Last week ended with a rule: where an atom sits tells you whether it loses or gains electrons. Three columns on the chart above the bench make that vivid. Group 1 on the far left has one outer electron to hand over. Group 7 needs one more to finish its shell. Group 0 at the edge needs nothing, and that stays true the whole way down, so it is the only one with no reactivity trend to explain. Noble gases even drift as single atoms, while gases like oxygen and chlorine travel in pairs. Within the other two columns, which member reacts hardest? Every group 1 metal meets water the same way: metal + water gives a metal hydroxide and hydrogen. Drop in lithium and it fizzes steadily. Sodium melts into a ball and skates across the surface. Potassium sets its own hydrogen alight with a lilac flame. In symbols the pattern never changes, only the metal: 2Na + 2H₂O → 2NaOH + H₂. A number in front of a formula says how many of that whole unit there are, so 3H₂O would mean three whole water molecules, which is 6 hydrogen atoms and 3 oxygen. Swap Na for K or Li and the pattern holds. *(drawing: One reaction, three tempers. The pattern down the column is the thing to remember.)* So why does it get fiercer further down? Every group 1 atom has one outer electron and reacts by losing it. Lithium is 2,1. Sodium is 2,8,1. Potassium is 2,8,8,1. Step down and that outer electron sits in a shell further from the nucleus, with more full shells packed in between. Those inner shells shield it from the pull of the protons. Further away and better shielded means held more loosely, so it comes off more easily. Easier to lose is what more reactive means here. *(drawing: Each step down puts another full shell between the outer electron and the protons pulling on it.)* Group 7 reacts by gaining an electron rather than losing one, so the same two effects push the other way. Chlorine is 2,8,7 and needs one more. Bromine's outer shell sits further out and behind more shielding, so an incoming electron feels a weaker pull. Iodine's is further still. Down group 7 the atoms grab electrons less strongly, so reactivity falls instead of rising. Their looks change down the column too: chlorine is a green gas, bromine an orange-brown liquid, iodine a dark grey solid that colours a solution brown. That is a separate pattern, but it makes them easy to tell apart. **Example.** Displacement puts the trend to work. A salt here means the compound a halogen makes with a metal, dissolved in water. On the bench, add chlorine water to colourless potassium bromide solution. Chlorine sits above bromine, so it is the stronger grabber: it takes the electrons and turns the bromide back into bromine. Cl₂ + 2KBr → 2KCl + Br₂, and the free bromine colours the solution. Run it the other way and nothing new forms. Iodine sits below bromine, so it cannot push bromine out of potassium bromide. **Recap.** A group 1 metal and water give a metal hydroxide and hydrogen, and the reaction gets fiercer down the column because the outer electron is further out and better shielded, so it is easier to lose. Group 7 gains an electron instead, so the same two causes make it harder and reactivity falls. A halogen displaces any halogen below it. Group 0 starts full, so it has no reactivity trend at all. ## Practice 24 questions on this page, each with its working shown. ## Needs first - [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) - [The Reactivity Series](https://lightmysky.com/learn/science/the-reactivity-series-mt_zsYW61cn_q) ## Opens up - [Ionic Bonding: Electron Transfer and Charged Lattices](https://lightmysky.com/learn/science/ionic-bonding-electron-transfer-and-charged-lattices-mt_sf24C4YLtN)