JEE Main 202623 JanuaryMorning Shift
- Exam
- JEE Main
- Year
- 2026
- Date
- 23 January
- Shift
- Morning Shift
- Subject
- Chemistry
- Chapter
- Classification of Elements and Periodicity in Properties
JEE Main 2026 · 23 January · Morning Shift · Chemistry · Classification of Elements and Periodicity in Properties
The correct trend in the first ionization enthalpies of the...
The correct trend in the first ionization enthalpies of the elements in the period of periodic table is :
Options
- A
- B
- C
- D
Correct answer
C.
Step-by-step solution
First ionization enthalpy generally increases across a period due to increasing nuclear charge and decreasing atomic radius. However, exceptions occur based on electron configuration stability.
For 3rd period elements, the approximate ionization enthalpy values are: Al (578), Si (787), P (1012), S (1000), Cl (1251) kJ/mol.
(1) Al has lower IE than Si because removing 3p¹ is easier than removing one electron from 3p².
(2) S has slightly lower IE than P despite being to the right because P has a half-filled p-orbital (3p³) which is more stable.
(3) Cl has the highest IE as it approaches a filled p-orbital.
The correct order is: Al < Si < S < P < Cl
For 3rd period elements, the approximate ionization enthalpy values are: Al (578), Si (787), P (1012), S (1000), Cl (1251) kJ/mol.
(1) Al has lower IE than Si because removing 3p¹ is easier than removing one electron from 3p².
(2) S has slightly lower IE than P despite being to the right because P has a half-filled p-orbital (3p³) which is more stable.
(3) Cl has the highest IE as it approaches a filled p-orbital.
The correct order is: Al < Si < S < P < Cl