Classification of Elements and Periodicity notes
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Classification of Elements and Periodicity: One-Page Formula Sheet
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Last updated: 26 October 2026
Formula sheet
Classification of Elements and Periodicity formulas
Classification of Elements and Periodicity — formula sheet
Formulas
- Isoelectronic species: higher nuclear charge → smaller size
- Effective nuclear charge Z_eff = Z − σ
- Pauling electronegativity difference predicts bond polarity
- Second IE is always higher than first
Key ideas
- Atomic radius decreases across a period, increases down a group
- Ionisation enthalpy generally rises across a period
- Exceptions: IE of N > O, Be > B
- Cl has more negative electron gain enthalpy than F
Traps to avoid
- Forgetting the N/O and Be/B exceptions
- Assuming F has the most negative electron gain enthalpy
- Mixing atomic and ionic radius trends
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