Classification of Elements and Periodicity in Properties Test - 8

Alkali metals have lowest ionization energy value in the respective period.

H₂⁺ is more stable than H₂⁻since,according to MOT,there are no any anti bonding electrons are present in the H₂+. In simple words when the two s-orbitals of the H atoms combine (overlap), there are two possible combinations - essentially they either add together (bonding MO), or they subtract (antibonding MO). The additive combination is called a (sigma) bonding orbital, while the subtractive combination is called an antibonding orbital (sigma*). Putting electrons into a bonding orbital helps to hold the atoms together (stabilizes the bond), whereas putting them into an antibonding orbital tends to drive them apart (destabilizes the bond). H₂⁺ has one electron shared between the two H nuclei, and it goes into the lowest energy orbital available... the bonding orbital. That helps to hold the H's together. H₂ has two electrons, and both can go into the bonding orbital (with opposite spins) and contibute to stability. That's better than only one electron in the bonding orbital, so H₂ is more stable than H₂⁺. Whereas in H₂^-, there are three electrons. The first two goes into the bonding orbital, but the third has to go into the antibonding orbital, which weakens the bond.

The presence of  five σ bonds and three π bondsfive σ bonds and three π bonds in compound  XeF₂O₃ has been  confirmed  by  its  IR spectra . 

When they arranged elements in the increasing order of their atomic weights, both of them observed that the chemical and physical properties of the elements repeated after a regular interval.

The transiiton metal in its highest oxidation state will have no desire to further loose electrons. It will act as an oxidizing agent where it will accept electrons and is reduced in a chemical reaction.