5.3.1/5.3.2 Transition elements and qualitative analysis GapFill

Transition elements are d-block elements that form ions with partially filled d-subshells. In the case of the first row of transition elements, from Period 4, this is the  4d6d5d3d subshell.

In a transition element complex, a central metal atom/ion is surrounded by ligands. Ligands are molecules or ions that can donate a lone pair of electrons to form a  cooperativecoordinatecognatecoadunate, or dative covalent, bond. The number of these bonds made to the metal is called the  chelatecomplexligandcoordination number. Ligands that are donate two lone pairs of electrons to the metal are said to be  'biaxial''bidentate'bimodal''binomial'. The most common shapes for transition element complexes are octahedral, square planar and   tetrahedralpyramidallineartrigonal planar. Reactions in which one ligand is replaced by another are called ligand   substitutioneliminationmodificationpermutation reactions.

When dissolved in water, several transition elements form  aquafluvialhydrosolvo complexes. These are almost always   lineartetrahedraloctahedralsquare planar, featuring the metal ion surrounded by   threetwofoursix water molecules. Some can act as acids in the presence of bases such as NaOH and NH₃, forming metal hydroxide species. If enough protons are lost to make the complex electrically neutral, a solid   preparatorprecipitatepreceptorperfuncturate forms, whose colour can be used to establish the identity of the metal ion.