The chapter ‘Periodic Classification and Periodicity in Properties’ is one of the most important chapters in the syllabus of JEE Main and JEE Advanced Entrance Examination. About 2-3 questions are being asked from this chapter. This article talks about important concepts, formulae and previous year questions related to this chapter. These chapter notes include all important topics related to Periodic Classification and Periodicity in Properties like need to classify elements, Law of Triads, Law of Octaves, Mendeleev's Periodic Table, Modern Periodic Table, Characteristics of Modern Periodic table, Periodic Trends in Properties of Elements etc. The concept given in this article is in concise form and can be used for revision before the examination.
Some previous year solved questions are given below:
The ionic radii (in) of N3-, O2- and F- respectively are
(a) 1.36, 1.40 and 1.71
(b) 1.36, 1.71 and 1.40
(c) 1.71, 1.40 and 1.36
(d) 1.71, 1.36 and 1.40
Number of Electrons in N3-, = 7 + 3 = 10
Number of Electrons in O2-, = 8 + 2 = 10
Number of Electrons in F-, = 9 + 1 = 10
Since, all the three species have equal electrons, they are isoelectronic.
For isoelectronic species as the negative charge increases, ionic radii increase.
Hence, ionic radii are in order
N3- > O2- > F-
Since option (c) only follows above order.
Hence, the correct option is (c).
Which one of the following alkaline earth metal sulphates has its hydrations enthalpy greater than its lattice enthalpy?
As we move down the group, size of metal increase.
So, Be < Ca < Sr < Ba
Since the size of Be is lowest in its group and has bigger size so BeSO4 breaks easily and lattice energy becomes smaller but due to lower size of Be, water molecules are gathered around and hence hydration energy increase.
Which among the following is the most reactive?
Cl2, Br2 and I2 are homonuclear diatomic molecular in which electronegativity of the combining atoms is same, so they are more stable and less reactive, whereas, I and Cl have different electronegativities and bond between them are polarized and reactive. Therefore, interhalogen compound are more reactive.
Which of the following represents the correct order of increasing first ionisation enthalpy for Ca, Ba, S, Se and Ar?
(a) Ca < S < Ba < Se < Ar
(b) S < Se < Ca < Ba < Ar
(c) Ba < Ca < Se < S < Ar
(d) Ca < Ba < S < Se < Ar
It is known that ionisation energy increase along a period from left to right and decreases down a group.
The position of given elements in the periodic table is as follows:
First row represent the group and remaining cells represent elements.
So, correct order of increasing first ionisation enthalpy is as shown below:
Ba < Ca < Se < S < Ar
Hence, the correct option is (c).
Identify the least stable ion amongst the following.
It is known that half filled or full filled are more stable than nearly half filled or nearly full filled orbitals.
Be- is the least stable ion, Be (1S22s2) has stable electronic configuration, addition of electron decreases stability.
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