Account for the following: Zn , Cd , Hg are considered as d-block elements but not as transition elements.

Zinc, cadmium and mercury are not considered as transition elements because of their electronic configuration. The general representation of the electronic configuration of these three elements is n - 1 d 10 ns 2 . The orbitals of these elements are completely filled when they are in their ground state as well as in their general oxidation state. Therefore, these elements are not transition elements.

Account for the following: Chromates change their colour when kept in an acidic solution.

The chromate ion CrO 4 2 - when placed in an acidic medium oxidises and changes to dichromate ion Cr 2 O 7 2 - . Also, the colour of chromate ion changes to orange red from yellow colour. The reaction is: 2 CrO 4 2 - + 2 H + ⇌ Cr 2 O 7 2 - + H 2 O .

Account for the following: Copper (I) compounds are white whereas copper (II) compounds are coloured.

n copper I ion all orbitals are completely filled so its compounds are white and diamagnetic. The electronic configuration of copper II ion is 1s22s22p63s23p63d9 . it has one unpaired electron so it is paramagnetic and forms blue coloured compounds.Read more on Sarthaks.com - https://www.sarthaks.com/379808/copper-compounds-are-white-and-diamagnetic-but-copper-compounds-coloured-paramagnetic n copper I ion all orbitals are completely filled so its compounds are white and diamagnetic. The electronic configuration of copper II ion is 1s22s22p63s23p63d9 . it has one unpaired electron so it is paramagnetic and forms blue coloured compounds.Read more on Sarthaks.com - https://www.sarthaks.com/379808/copper-compounds-are-white-and-diamagnetic-but-copper-compounds-coloured-paramagnetic n copper I ion all orbitals are completely filled so its compounds are white and diamagnetic. The electronic configuration of copper II ion is 1s22s22p63s23p63d9 . it has one unpaired electron so it is paramagnetic and forms blue coloured compounds.Read more on Sarthaks.com - https://www.sarthaks.com/379808/copper-compounds-are-white-and-diamagnetic-but-copper-compounds-coloured-paramagnetic n copper I ion all orbitals are completely filled so its compounds are white and diamagnetic. The electronic configuration of copper II ion is 1s22s22p63s23p63d9 . it has one unpaired electron so it is paramagnetic and forms blue coloured compounds.Read more on Sarthaks.com - https://www.sarthaks.com/379808/copper-compounds-are-white-and-diamagnetic-but-copper-compounds-coloured-paramagnetic In copper (I) ions all the orbitals are completely filled and hence its compounds are white and diamagnetic in nature. One Unpaired electron is present in copper (II) ions and hence they are blue coloured compounds and are paramagnetic in nature. They also show d - d transition.

Give reason and select one atom/ion which will exhibit asked property : Cr or Cu (High melting and boiling point)

Chromium ( Cr ) has a higher melting point because of the half filled stability. Its electronic configuration is 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 4 s 1 3 d 5 . Due to the half filled d- orbital, the unpaired electrons forms strong intermetallic bonds hence resulting in high melting point and boiling point. Whereas, the electronic configuration of copper ( Cu ) is 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 4 s 2 3 d 9 . It does not have half filled stability.

Calculate the spin only moment of Co 2 + Z = 27 by writing electronic configuration of Co and Co 2 +

The atomic number of cobalt is 27 and the electronic configuration of cobalt is Co = Ar 4 s 2 3 d 7 . Electronic configuration of Co 2 + = Ar 3 d 7 Spin only moment is calculated by using the formula μ = n n + 2 , n = number of unpaired electrons μ = 3 3 + 2 = 3 . 92 B . M

Give reasons: Sc 3 + is a colourless in aqueous solution whereas Ti 3 + is coloured.

Transition metal ions show colour due to the presence of unpaired electrons in d orbital. The atomic number of Sc is 21 and the atomic number of Ti is 22 . The electronic configuration of Sc 3 + = Ar 3 d 0 ⇒ 0 unpaired electron. The electronic configuration of Ti 3 + = Ar 3 d 1 4 s 0 ⇒ 1 unpaired electron Therefore, the aqueous solution of Ti 3 + ion is coloured.