Classification of Elements and Periodicity for NEET UG
The periodic table is not a list to memorise but a pattern to understand. Once you see why atomic size, ionisation energy and electronegativity change, the trends follow.
ChemistryClass 1174 MCQs2 lessons12 flashcards3 memory tricks
Practise Classification of Elements and Periodicity free
What you'll learn
- The modern periodic table
Place an element in its period, group and block from its electronic configuration. - Periodic trends
Explain trends in atomic radius, ionisation enthalpy, electron gain enthalpy and electronegativity.
Memory tricks
Li, Na, K, Rb, Cs, Fr.
Ionisation energy and electronegativity increase across a period and up a group, so they are highest at the top right (F is the most electronegative). Atomic radius does the opposite.
N > O and Be > B in ionisation energy: N has a stable half-filled 2p³ and Be a filled 2s², so it costs more to remove an electron.
Try 3 NEET-style questions
Q1. Among Na, Mg, Al and Si, the element with the highest first ionisation enthalpy is
- Na
- Al
- Si
- Mg
Show answer
Answer: (3) Si
First ionisation enthalpies (kJ mol⁻¹): Na ≈ 496, Al ≈ 577, Mg ≈ 738, Si ≈ 786. Silicon has the highest, as nuclear charge rises across the period.
Q2. Newlands' law of octaves, relating every eighth element, was found to work well only up to
- calcium
- uranium
- iron
- hydrogen
Show answer
Answer: (1) calcium
Newlands noted that every eighth element had similar properties, like octaves in music. His law seemed to be true only up to calcium.
Q3. Given below are two statements. Statement I: Ionisation enthalpy is always positive. Statement II: The second electron gain enthalpy of oxygen is negative. In the light of the above statements, choose the correct answer.
- Both Statement I and Statement II are true
- Statement I is true but Statement II is false
- Both Statement I and Statement II are false
- Statement I is false but Statement II is true
Show answer
Answer: (2) Statement I is true but Statement II is false
Statement I is true: removing an electron always needs energy. Statement II is false: adding a second electron to O⁻ needs energy, so it is positive.
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