H2 Chemistry Notes: CORE IDEA 2, Topic 5 - The Periodic Table
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Q: What does H2 Chemistry Notes: CORE IDEA 2, Topic 5 - The Periodic Table cover?
A: Link periodic trends, Period 3 oxides/chlorides, and Group 2/17 reactivity to Core Idea 2 (The Periodic Table) requirements for the 2026 H2 Chemistry syllabus.
Periodic trends inform everything from bonding predictions to qualitative analysis.
This guide explains electron configuration roots of the trends, highlights compulsory case studies (Period 3 oxides and chlorides, Groups 2 and 17), and provides exam-ready examples.
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Status: SEAB H2 Chemistry (9476, first exam 2026) syllabus and Chemistry Data Booklet last checked 2026-01-13 (both PDFs last modified 2026-01-13). Core Idea 2 Topic 5 remains assessed across Papers 1–3.
1 General Periodic Trends
| Property | Across a period (left → right) | Down a group | Key reasoning |
| Atomic radius | Decreases | Increases | Effective nuclear charge vs shell number. |
| Ionisation energy | Increases (with small dips) | Decreases | Stronger nuclear attraction vs increased shielding. |
| Electronegativity | Increases | Decreases | Attraction for bonding electrons. |
