The statement that is not correct for the periodic classification of elements is
Correct answer: C. For transition elements, the 3d-orbitals are filled with electrons after 3p-orbitals and before 4s-orbitals.
- A. The properties of elements are periodic functions of their atomic numbers.
- B. Non-metallic elements are fewer in number than metallic elements.
- C. For transition elements, the 3d-orbitals are filled with electrons after 3p-orbitals and before 4s-orbitals.
- D. The first ionisation enthalpies of elements generally increase with an increase in atomic number as we move along a period.
Explanation
Option C is the correct answer because it incorrectly states the order of filling for transition elements. According to the Aufbau principle, the 3d-orbitals are filled after the 4s-orbitals, not before. Therefore, the correct electron filling order is 3s, 3p, 4s, 3d, 4p.Option A is correct because the periodic table is indeed based on the properties as a function of atomic numbers. Option B is correct because there are indeed more metallic elements than non-metallic elements in the periodic table. Option D is correct as the first ionisation enthalpies generally increase across a period due to increasing nuclear charge.
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About Periodic Properties and Trends
Periodic properties arise from electron configuration and effective nuclear charge, producing trends in atomic and ionic radius, ionization energy, electron affinity, electronegativity, metallic character and reactivity. Comparisons run across periods and down groups, with attention to common exceptions. The topic also relates these trends to the behavior of s-block and p-block elements.
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