Question

What is covalency exactly? What is it in terms of lanthanides? What about transition metals?

Answer 1

Covalency is the number of bonds that can be formed by particular atom of an element sharing its electrons with other atom having empty/not full-filled orbitals(s,p,d,or f) so to become stable.The bond formed by sharing electrons called covalent bond.So covalency also can be termed as maximum number of covalent bond an atom can form to attain stability in its normal uncharged state.The simplest atom, hydrogen has the capacity to form one bond; that is, it can attach itself to one other atom to form a molecule. Oxygen atom can form two bonds and nitrogen atoms can form 3 within a molecule.

Lanthanides are the rare earth elements.In terms of lanthanides its called valency.Valency is showing the number of bonds that atom of an element forms by donating or accepting electrons so become element is stable.Lanthanides form ionic bond.They rarely form covalent bond.Lanthanide series has a valency of +3.But some of the elements in the lanthanide series have multiple possible valencies(ranging from +2 to +4).

The elements between the group number 3 to 12 in the periodic table are called transition metals.The two outermost shells of transition metals are incomplete.The bonding in transition metal complex is called coordinate bonding/dative covalent bonding.This is similar to normal covalent bonding except both electrons are donated from one species.Transition metals readly form alloys and lose electrons to form stable cations.