7. Four transition series:
a. 3d – transition series. The transition elements with atomic number 21( Sc) to 30( Zn) and having incomplete 3d orbitals is called the first transition series.
b. 4d – transition series. It consists of elements with atomic number 39( Y) to 48( Cd) and having incomplete 4d orbitals. It is called second transition series. c. 5d – transition series. It consists of elements with atomic number 57( La), 72( Hf) to 80( Hg) having incomplete 5d orbitals. It is called third transition series.
d. 6d – transition series. It consists of elements with atomic number 89( Ac), 104( Rf) to 112( Uub) having incomplete 6d orbitals. It is called fourth transition series.
8. General Characteristics of transition elements:
a. Metallic character: All transition elements are metallic in nature, i. e. they have strong metallic bonds. This is because of presence of unpaired electrons. This gives rise to properties like high density, high enthalpies of atomization, and high melting and boiling points.
b. Atomic radii: The atomic radii decrease from Sc to Cr because the effective nuclear charge increases. The atomic size of Fe, Co, Ni is almost same because the attraction due to increase in nuclear charge is cancelled by the repulsion because of increase in shielding effect. Cu and Zn have bigger size because the shielding effect