Generated by claude-sonnet-4-6 · 2026-06-15 06:52 · grounding rag
Model Answer
(a) Two advantages of using atomic number as the basis of classification:
- Atomic number is a unique, fixed property of each element, leaving no ambiguity in an element's position in the table.
- It removes anomalies of Mendeleev's table (e.g., cobalt and nickel are placed correctly based on atomic number, not atomic mass).
(b) Electronic configurations:
- Element X (atomic number 13): 2, 8, 3
- Element Y (atomic number 20): 2, 8, 8, 2
Explanation
- For part (a), examiners expect any two valid advantages — uniqueness of atomic number and removal of Mendeleev's anomalies are the most standard ones. Avoid vague answers.
- For part (b), simply fill shells in order (2, 8, 8, 2 for 20 electrons). These are straightforward but students often make errors with Y — remember the 3rd shell can hold up to 18, but it stabilises at 8 before the 4th shell begins filling.