The Modern Periodic Law, given by Moseley in 1913, states that the physical and chemical properties of elements are periodic functions of their atomic number (), not of atomic mass as Mendeleev's law had claimed. This resolved the anomalies that embarrassed the older ordering: the heavier (58.93 u) is correctly placed before the lighter (58.71 u), and the hea
Classification of Elements and Periodicity in Properties
Class 117 previous-year questions from this chapter every option and the correct answer, free · where the marks are
1. Modern periodic table and electronic basis
Exam focus: The modern periodic law orders elements by atomic number, not atomic mass — the switch from Mendeleev's basis that fixed anomalies like the Co/Ni and Ar/K ordering. Hydrogen's dual placement (loses one electron like an alkali metal, needs one like a halogen) is a recurring "which group" trap.
Classification of Elements and Periodicity — Full Chapter
Next Toppers - 11th Science
Full-chapter one-shot covering the modern periodic table and its electronic basis. Not a strongly-preferred channel, but an established CBSE Class 11 coaching channel; no preferred-channel equivalent could be verified in time.
ChemistryNEET 2025show ▾Which among the following electronic configurations belong to main-group elements?
A. · B. · C. · D. · E.
Choose the correct answer from the options given below:
- A.B and E only
- B.A and C only✓
- C.D and E only
- D.A, C and D only
Solution
Main-group elements have their outermost electrons in or orbitals: (Na) and (I). B and D are -block, E is -block (a actinoid configuration). So A and C.
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Save for spaced revision (free account)ChemistryNEET 2022show ▾The IUPAC name of an element with atomic number 119 is:
- A.ununoctium
- B.ununennium✓
- C.unnilennium
- D.unununnium
The worked solution is part of a paid pack.
2. Periodic trends: radius, ionisation enthalpy, electron gain enthalpy, electronegativity
Exam focus: Chlorine, not fluorine, has the most negative electron gain enthalpy in its group — fluorine's small size packs the incoming electron into an already-crowded 2p subshell, offsetting its higher electronegativity. Ionisation enthalpy also dips at boron (below Be) and at oxygen (below N), because removing an electron from a filled 2s² or half-filled 2p³ costs extra — the "always rises across a period" rule breaks at exactly these two points.
Classification of Elements and Periodicity — Full Chapter
Next Toppers - 11th Science
Same full-chapter video; periodic trends (radius, ionisation enthalpy, electron gain enthalpy, electronegativity) are covered within it.
ChemistryNEET 2025show ▾Which of the following statements are true?
A. Unlike Ga, which has a very high melting point, Cs has a very low melting point.
B. On the Pauling scale, the electronegativity values of N and Cl are not the same.
C. Ar, , , and are all isoelectronic species.
D. The correct order of the first ionisation enthalpies of Na, Mg, Al and Si is Si > Al > Mg > Na.
E. The atomic radius of Cs is greater than that of Li and Rb.
Choose the correct answer from the options given below:
- A.A, B and E only
- B.C and E only✓
- C.C and D only
- D.A, C and E only
Solution
Ar, , , and all have 18 electrons (C true); atomic radius grows down Group 1, so Cs > Rb > Li (E true). Ga in fact has a low melting point (A false); N and Cl share the Pauling value 3.0 (B false); Mg > Al in first ionisation enthalpy (D false). Hence C and E.
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Save for spaced revision (free account)ChemistryNEET 2024show ▾Arrange the following elements in increasing order of electronegativity: N, O, F, C, Si.
Choose the correct answer from the options given below:
- A.Si < C < O < N < F
- B.O < F < N < C < Si
- C.F < O < N < C < Si
- D.Si < C < N < O < F✓
Solution
Electronegativity rises across a period and falls down a group: Si < C < N < O < F.
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Save for spaced revision (free account)ChemistryNEET 2024show ▾Arrange the following elements in increasing order of first ionisation enthalpy: Li, Be, B, C, N.
Choose the correct answer from the options given below:
- A.Li < B < Be < C < N✓
- B.Li < Be < C < B < N
- C.Li < Be < N < B < C
- D.Li < Be < B < C < N
Solution
Ionisation enthalpy generally rises across the period, but Be (, filled subshell) is higher than B (whose electron is easier to remove). Order: Li < B < Be < C < N.
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