Classification of Elements and Periodicity in Properties
3 solved JEE Chemistry previous year questions on Classification of Elements and Periodicity in Properties, each with the correct answer and a full explanation.
Q1
Which of the following element has the highest ionization enthalpy?
✓ Correct answer: a) Boron
ExplanationBoron has the highest ionisation enthalpy amongst the following.Ionisation enthalpy decreases down the group and increases across the period.
Q2
The IUPAC symbol for the element with atomic number 119 would be :
✓ Correct answer: d) Uue
ExplanationThe element with atomic number 119 is not yet officially discovered, so it has a temporary systematic IUPAC name.According to IUPAC rules: 1 → un 1 → un 9 → en Combine them: un-un-en → Uue Symbol: Uue
Q3
The successive 5 ionisation energies of an element are 800, 2427, 3658, 25024 and 32824 kJ/mol, respectively. By using the above values predict the group in which the above element is present :
✓ Correct answer: d) Group 13
ExplanationIonization enthalpy = the energy required to remove one electron from an isolated gaseous atom.General trend: Increases across a period (left → right) Decreases down a group Electron gain enthalpy = energy released when an atom gains an electron.More negative = stronger tendency to gain electrons Small size of fluorine Fluorine's atomic radius is very small.When an extra electron is added to fluorine, it goes into the already crowded 2p orbital, where electron–electron repulsion is very high.This reduces the stability gained by accepting that electron.2. Chlorine has larger size Chlorine's 3p orbital is bigger, so it can accommodate the incoming electron more easily with less repulsion.Hence, it releases more energy (i.e., more negative electron gain enthalpy).Both Statement-I and Statement-II are true
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