Lesson Explainer: Physical Properties of Transition Metals Chemistry

In this explainer, we will learn how to describe and compare the physical properties of transition metals.

The transition metal elements can be found in the d-block domain of the periodic table. They are a diverse collection of metals and they have many important uses. The transition metals can be compared with the post-transition metal elements because they are solid, lustrous, and good conductors of heat and electricity.

The different applications of the transition metal elements can be understood if we take some time to understand the physical properties of individual transition metals and how physical properties change across the block of transition metal elements.

Let us first consider the atomic mass values of the period four transition metal elements. The following figure shows that atomic mass values generally increase as we move from scandium on the left-hand side through to copper on the right-hand side. Nickel is an exception to the trend because it has an atomic mass value that is smaller than the atomic mass value of cobalt.

We can also consider how atomic radii change as we move from scandium through to copper. Atomic radius values do not systematically increase or systematically decrease as we move across the row of period four transition metals. The relationship between atomic radii values and atomic numbers is quite complex and it can only be explained if we consider the electronic configurations of these elements. The following figure uses a combination of condensed notations and single-sided arrows to show how the electron configuration changes across the period four metal elements.

Initially, the radius begins to decrease as the nuclear charge increases. The nuclear charge increases due to an increasing number of protons in the atom’s nucleus. The additional electrons continue to fill the 3d orbital and they are pulled closer to the nucleus.

However, as we get to chromium, the increased number of electrons in the 3d orbital generates enough repulsion between the electrons to halt the decrease in atomic radii and the atomic radius values remain essentially constant from chromium through to copper.

Density is related to the mass of an object and its volume, and as we move from left to right across period 4, the mass of the atom increases. In terms of the atomic radius, as we previously stated, the radius decreases but not in a uniform manner. When combined, these two general trends create a trend of increasing density as we move across period 4, as can be seen in the graph below.

It is worth noting here that the transition metals generally have higher densities than s-block metals from the same period. Potassium and calcium are both period four metals, but they are not transition metal elements. Potassium and calcium have density values of just 0.89 g/cm³ and 1.54 g/cm³.

There does not seem to be any clear overall trend or pattern between melting points and atomic numbers for the period four transition metal elements. This can be seen in the following figure.

However, one definitive statement we can make is with respect to the period 4 s-block metals. Potassium has a melting point of 336.5 K and calcium has a melting point of 1‎ ‎115 K, and so the period 4 transition metals have higher melting points than the corresponding s-block metals. Metallic bonding is related to melting point, indicating that the period 4 transition metals have stronger metallic bonds than potassium and calcium.

We can classify the transition metals in terms of their magnetic properties. Some of the metals are paramagnetic, and others are diamagnetic. An atom, ion, or molecule is considered to be paramagnetic when it contains atoms with unpaired electrons. These unpaired electrons have a magnetic dipole moment, and they act like tiny magnets because they are attracted toward externally applied magnetic fields. The magnitude of the magnetic moment in a paramagnetic substance tends to be larger if the substance has a greater number of unpaired electrons.

A diamagnetic substance has no overall magnetic moment because all of its orbitals are filled with paired electrons. Diamagnetic substances almost always repel externally applied magnetic fields.

The electronic configuration of atoms, ions, and molecules can usually be used to determine if substances are diamagnetic or paramagnetic. Using vanadium as an example, atoms of vanadium have the electronic configuration. The term shows that vanadium has at least one unpaired electron and this fact can be used to determine that vanadium is a paramagnetic material.

The nickel, iron, and cobalt elements and alloys exhibit a rather interesting type of magnetism that is known as ferromagnetism. Ferromagnetism is the basic mechanism by which certain materials form permanent magnets. The nickel, iron, and cobalt elements and alloys exhibit ferromagnetism because of their unusual structures.

The period 4 transition metals have remarkably different interactions with other substances and remarkably different chemical reactivities. Copper has a remarkably low rate of reactivity with most gaseous molecules whereas iron tends to rust when it is left out in the open where it can interact with oxygen and water molecules in the air. Other metals like scandium can react vigorously with water if they are divided into fine particles. The scandium metal tends to produce hydroxide ions as it displaces hydrogen atoms in water molecules:

The use of the transition metals is discussed more comprehensively in another explainer, but it is nonetheless important to state here that many transition metals are used in industry because of their catalytic activity.

Finely divided nickel metal is used as a catalyst to produce margarine through hydrogenation processes. Divided iron is used as a catalyst to enhance the Haber–Bosch process, which is an artificial nitrogen fixation process and the main industrial procedure for producing ammonia.

Vanadium pentoxide is a well-known transition metal compound that can be used as a catalyst to enhance the production of sulfuric acid through the contact process:

Finally, manganese dioxide can be used to catalyze the decomposition of hydrogen peroxide:

The chemistry explaining the catalytic activity of the transition metal elements and transition metal element compounds is complicated. However, much of the catalytic activity can be attributed to the presence of the 4s and 3d electrons and the fact that they allow reactions to take place through different chemical pathways. Alternate pathways could include, for example, the formation of intermediate complex ions or the formation of complexes of reactant molecules that are adsorbed on catalyst surfaces.

Transition elements usually form colorful compounds. The colors arise from the absorption of certain wavelengths of white light by the transition metal and its compound. This absorption results in only some of the wavelengths of white light passing through the solution.

When hydrated copper(II) sulfate crystals are dissolved in water, the complex ion is formed. This ion tends to absorb both red and orange wavelengths, as can be seen in the diagram below.

The color wheel below indicates the relationship between the wavelengths of light absorbed by different cations and the corresponding color they appear to the human eye. When red and orange light is absorbed, the opposite colors on the wheel are observed by the human eye and hence the solution will appear to be blue. The light energy is absorbed by electrons in ions with partially filled d orbitals.