--- title: "Main-Group Chemistry: What Changes Down a p-Block Group" description: "Members of a p-block group share a valence-electron count, but their sizes, bonding and stable oxidation states can differ. Heavier elements can form compounds with Lewis counts above eight. Named hyd" canonical: https://lightmysky.com/learn/science/main-group-chemistry-what-changes-down-a-p-block-group-mt_wq15-pBrI5 source: https://lightmysky.com/learn/science/main-group-chemistry-what-changes-down-a-p-block-group-mt_wq15-pBrI5.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`. # Main-Group Chemistry: What Changes Down a p-Block Group Members of a p-block group share a valence-electron count, but their sizes, bonding and stable oxidation states can differ. Heavier elements can form compounds with Lewis counts above eight. Named hydride and oxide families show how bond overlap, electronegativity and metallic character affect their chemistry. Subject: Science · Area: Chemistry · Ages 19 to 20 Page: https://lightmysky.com/learn/science/main-group-chemistry-what-changes-down-a-p-block-group-mt_wq15-pBrI5 ## Ready when they can - Explains the inert-pair effect and identifies commonly favoured lower oxidation states of heavy group 13 to 15 elements - Distinguishes ordinary octet-based Lewis structures from higher coordination in heavier p-block compounds without treating Lewis counts as literal atomic-shell occupancy - Compares named group 15 hydrides and oxides using bond overlap, electronegativity and metallic character, with oxide oxidation states specified ## Lesson: What changes as you go down a p-block group For neutral main-group atoms, groups 1 and 2 have one and two valence electrons. For groups 13 to 18, subtract ten from the group number. Helium is the group 18 exception, with two. A shared valence count helps explain similar chemistry within a group. Atomic sizes generally increase down a group, but bonding and electron energies also matter. *(drawing: The count increases across these groups. Helium has two valence electrons.)* In ordinary octet-based Lewis structures, C, N, O and F have at most eight surrounding electrons. Each single bond counts two at each end. BF3 has an incomplete octet at B. Gaseous PCl5 has five P-Cl bonds, giving a Lewis count of ten at P. Silicon has six F neighbours in [SiF6]^2-. Higher coordination does not mean all counted electrons are confined to one atom or that occupied d orbitals are required. Heavy group 13 to 15 elements often favour lower oxidation states, including Tl(I), Pb(II) and Bi(III). This inert-pair effect means the valence s pair is less available for bonding. The energy gained from bonding may not offset the cost of involving that pair. Ligands and conditions affect the balance. Roman numerals give formal oxidation states, not bond counts or proof of actual electron transfer. *(drawing: Each group counts one P-Cl bonding pair. This is electron bookkeeping, not a drawing of the molecule.)* Group 15 hydride E-H bonds generally lengthen and weaken down the group as overlap with H 1s becomes less effective; thermal stability falls. Electronegativity generally falls and metallic character rises. Compare named oxides with oxidation states specified: N2O5, nitrogen(V) oxide, is acidic; Bi2O3, bismuth(III) oxide, is basic. These examples do not establish a universal rule for every bond or oxide. **Recap.** Group members share valence counts, not identical chemistry. Lewis counts, oxidation states and bond trends describe different aspects of a specified compound. *Lesson, questions and flashcards written for this dataset.* ## 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 - [Trends Across Period 3: Radius, Ionisation Energy and Melting Point](https://lightmysky.com/learn/science/trends-across-period-3-radius-ionisation-energy-and-melting-point-mt_stFFQ6GPIh) - [Heteronuclear Diatomics and Polarity in Orbital Terms](https://lightmysky.com/learn/science/heteronuclear-diatomics-and-polarity-in-orbital-terms-mt_thdxFqyHJV)