Occurrence, Preparation, and Properties of Transition Metals and Their Compounds
Transition metals are defined as those elements that have (or readily form) partially filled d orbitals. As shown in the figure below, the d-block elements in groups 3–11 are transition elements. The f-block elements, also called inner transition metals (the lanthanides and actinides), also meet this criterion because the d orbital is partially occupied before the f orbitals.
The d orbitals fill with the copper family (group 11); for this reason, the next family (group 12) are technically not transition elements. However, the group 12 elements do display some of the same chemical properties and are commonly included in discussions of transition metals. Some chemists do treat the group 12 elements as transition metals.
The d-block elements are divided into the first transition series (the elements Sc through Cu), the second transition series (the elements Y through Ag), and the third transition series (the element La and the elements Hf through Au). Actinium, Ac, is the first member of the fourth transition series, which also includes Rf through Rg.
The f-block elements are the elements Ce through Lu, which constitute the lanthanide series (or lanthanoid series), and the elements Th through Lr, which constitute the actinide series (or actinoid series). Because lanthanum behaves very much like the lanthanide elements, it is considered a lanthanide element, even though its electron configuration makes it the first member of the third transition series. Similarly, the behavior of actinium means it is part of the actinide series, although its electron configuration makes it the first member of the fourth transition series.
Valence Electrons in Transition Metals
Review how to write electron configurations, covered in the tutorial on electronic structure and periodic properties of elements. Recall that for the transition and inner transition metals, it is necessary to remove the s electrons before the d or f electrons. Then, for each ion, give the electron configuration:
For the examples that are transition metals, determine to which series they belong.
For ions, the s-valence electrons are lost prior to the d or f electrons.
(a) Ce3+[Xe]4f1; Ce3+ is an inner transition element in the lanthanide series.
(b) Pb2+[Xe]6s25d104f14; the electrons are lost from the p orbital. This is a main group element.
(c) titanium(II) [Ar]3d2; first transition series
(d) americium(III) [Rn]5f6; actinide
(e) palladium(II) [Kr]4d8; second transition series
The transition elements have many properties in common with other metals. They are almost all hard, high-melting solids that conduct heat and electricity well. They readily form alloys and lose electrons to form stable cations. In addition, transition metals form a wide variety of stable coordination compounds, in which the central metal atom or ion acts as a Lewis acid and accepts one or more pairs of electrons. Many different molecules and ions can donate lone pairs to the metal center, serving as Lewis bases. In this tutorial, we shall focus primarily on the chemical behavior of the elements of the first transition series.