Explanation of reactivity trends in Group 1 and Group 17 elements:
Reactivity trend in Group 1 (Alkali metals):
Li < Na < K < Rb < Cs
Group 1 elements are highly reactive metals. Their reactivity depends on how easily they can lose their single valence electron.
As we move down the group:
• Atomic size increases.
• The distance between the nucleus and the valence electron increases.
• Shielding effect increases.
• Ionisation energy decreases.
Due to lower ionisation energy, the valence electron is lost more easily. Hence, reactivity increases down the group, making cesium the most reactive and lithium the least reactive among Group 1 elements.
Reactivity trend in Group 17 (Halogens):
F > Cl > Br > I
Group 17 elements are non-metals and their reactivity depends on their tendency to gain one electron.
As we move down the group:
• Atomic size increases.
• Attraction of nucleus for incoming electron decreases.
• Electron affinity decreases.
Fluorine has the smallest size and highest electronegativity, so it gains an electron most easily. Therefore, reactivity decreases down the group.
Conclusion:
In Group 1, reactivity increases down the group due to decreasing ionisation energy. In Group 17, reactivity decreases down the group due to decreasing electron affinity and increasing atomic size.
Given below are two statements:
Statement (I): According to the Law of Octaves, the elements were arranged in the increasing order of their atomic number.
Statement (II): Meyer observed a periodically repeated pattern upon plotting physical properties of certain elements against their respective atomic numbers.
In the light of the above statements, Choose the correct answer from the options given below:
The correct orders among the following are:
[A.] Atomic radius : \(B<Al<Ga<In<Tl\)
[B.] Electronegativity : \(Al<Ga<In<Tl<B\)
[C.] Density : \(Tl<In<Ga<Al<B\)
[D.] 1st Ionisation Energy :
In\(<Al<Ga<Tl<B\)
Choose the correct answer from the options given below :