The set of elements known as transition metals being classified under the d-blocks of the periodical chart of elements. These components have d-orbitals that are only partially occupied. Mercury, cadmium, and zinc are not considered transition metals as their d orbitals are completely filled in their ground state. However, their oxidation state of +2 corresponds to the electronic configuration (n-1)d10 ns2. The group of elements referred to as transition metals are those that are characterized by having two valence electron shells instead of one. Transitions metals exist in existence and may be found on every continent. They can be found as pure metals, but they can also exist in compounds in the Earth’s crust. In order to extract the metals from these compounds, they are extracted using either the pyrometallurgical process or the hydrometallurgical method (Cheng, et al., 2018).
Figure 1: Transition Metals
1. What are transition metals?
The most common definition of transition metals comes from the IUPAC. By this concept, a transitioning metal is an element whose d-subshell is only half full, allowing it to form inadequate cations. This is why transitions metals are distinct from many other elements in their characteristics. Sometimes, these elements are referred to as d-block elements, but in most cases, they are called B-group elements (Stringer, Owen & Kemp, 2020).
1.1. Main transition series
Transition metals are heavy and very hard. They are grouped into four main transition series based on their atomic structures. In addition, they are categorized into four types based on their electron configuration. These include the first, second, third and four transition series. These elements are largely the same, but exhibit a slightly different electron configuration.
Figure 2: Transition Series
1.2. Intra-molecular bonds
As transition metals are generally characterized by their partially filled d-subshell, which allows reagents to form a temporary bond with the metal. This partially filled d-subshell also helps to weaken intra-molecular bonds, which results in lower activation energy. Because more molecules are able to use their energy, the reactions rates increase with lower activating energies.
2. Elements belonging to group of transition metals
Following elements belongs to the group of transition elements (Ali, 2022).
1. Scandium, Titanium, Vanadium, Chromium, Manganese, Iron, Cobalt, Nickel
2. Yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium,
3. Lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum,
4. Actinium, Rutherfordium, Hahnium, Seaborgium, Bohrium, Hassium, Meitnerium, Ununnilium, Unununium,
2.1. Tungsten
Tungsten is a transition metal, which means that it belongs to a group of metals whose oxidation state is higher than that of the corresponding element. Its lower oxidation state is completely unstable. The complex halide of tungsten is W6X12 and it contains two electrons in each shell. In its oxidation state zero, it is present as a carbonyl compound.
2.2 Ruthenium
Ruthenium belongs to the group of transition metals. It has seven different isotopes, each different in mass. The masses number indicates the quantity of protons and neutrons. This number may vary with different elements .Ruthenium was discovered in 1925 by two scientists. Otto Berg and Walter Noddack discovered this element by bombarding a columbite sample with an electron beam.
2.3 Vanadium
Vanadium’s is a member of the family of metals that undergo a transformation. Due of its low density, it is frequently found in alloys. Vanadium is a soft, malleable metal, but its properties are greatly affected by impurities. The most important uses of vanadium are in high-speed tools, alloy steel, and springs. Vanadium is a metal that has a high melting point. Its oxidation number is a stable +5. The element was first discovered in Mexico by Andres Manuel del Rio, a Spanish scientist and professor at the Royal School of Mines in Mexico.
2.4 Bohrium
Bohrium is a man-made chemistry elements, denoted by the symbol Bh and having the atomic number 107. It is rare and highly corrosion resistant, and is one of the transition metals. Bohrium is also a highly radioactive element, and there are several different isotopes of the element. The stable isotope 270Bh has a half-life of 61 seconds, and the less stable isotope 278Bh has a half-life of 690 seconds.
3. Main features and characteristics
They are much denser than s-block elements and exhibit a gradual increase in density from scandium to nickel. The increase in density is attributed to small, irregular decreases in metallic radii and an increase in atomic mass.
3.1. Physical properties
The physical properties of transition metals make them useful for a variety of applications. They are readily hammered into shapes, and exhibit a high degree of hardness. They also form a wide range of alloys. Their oxidation state, their melting points, their catalytic activities, and their d-subshells are factors which make them useful for chemical processes. Their high melting points make them great conductors of electricity and heat.
3.2. Structural properties
These metals have high tensile strength and density. They are also very malleable. While some require very high temperatures to become malleable, most of them possess useful structural properties. Their other main features are their electronic structure, magnetism, chemical properties, and colors.
3.3. Electronic structure
Several recent studies have investigated the electronic structure of transition metals under pressure. These investigations include comparisons between group V and group VII transition metals. These comparisons are important in understanding the electronic structure of these materials. According to the atomic structure of neutrality cobalt, all of the atom’s electrons are located in the more stable 4s orbital. This is different from the higher-energy 3d orbitals, where cobalt loses electrons. Ionic combinations of Co2+ and Co3+ are as follows:
Co: 1s2 2s2 2p6 3s2 3p6 4s2 3d7
Co3+: 1s2 2s2 2p6 3s2 3p64s13d5
Co2+: 1s2 2s2 2p6 3s2 3p6 4s0 3d7
3.4. Magnetism
The magnetism of transition metals can be discussed using the Anderson model of 3d virtual states. The Anderson model explains experimental data concerning the formation of spin density waves in Cr and FeRh, and offers a new view on the transition of these materials from their antiferromagnetic state to their ferromagnetic state.
Figure 3: Anderson model
3.5. Chemical properties
Transition metals are a class of metals. These may be alloyed with another metals and have a high hardness. As a result, they have excellent catalytic properties. In addition, they do not react with water.
3.5.1. Strong metallic bonding
Strong metallic atomic bonding is a result of the presence of two or more valence electrons on a metal atom. This behavior is caused by valence electrons moving into the conducting bands, a process known as de-localization. This leads to increased intermetallic covalent bonds between the atoms.
3.5.2. Non-direccional
Metallic bonding is mainly non-directional, in typical metals, it favors structures that correspond to the closest packing of spheres. However, in some cases, this bonding is affected by covalent interactions, which lead to more complex structures.
3.6. Catalytic activity
These transition metals are effective catalysts because they lend their electrons to other molecules, increasing the rate of a reaction. The activity of transition metals is much higher than that of metal oxides. The catalysts in these compounds participate in all steps of the oxidation process.
3.7. Colors
Changing oxidation states of transition metals can produce different colors in a complex. These complexes contain a metal ion at their centre, surrounded by ligands that are attached by dative covalent bonds. Their apparent color depends on a combination of reflection and transmission. Transition metal complex ions are usually colored. To generate colors, the d orbitals must be partially filled. These complexes are often octahedral in nature, which means there are six simple ligands surrounding the central metal ion. Other complexes contain multidentate ligands, which are harder to visualize.
Figure 4: Complex Ion
Figure 5: The color of some transition metals ions is given in the table
4. Uses and properties of transition metals
Transition metals are a class of element that are unique among the elements in nature. Because of their very high valence electron count, they tend to form compounds with unusually large numbers of members. These valence electrons also affect the properties of the elements. While most transition metals have similar properties, there are some notable differences. For example, some transition metals have very different magnetic fields. These include elements such as cobalt, nickel and iron (Cheng, et al., 2018; Stringer, Owen & Kemp, 2020).
4.1. Essential to biological life
These metals are essential to biological life some may be toxic or nontoxic, these elements have many practical applications. Some transition metals are essential for transporting oxygen throughout the body.
4.2. Corrosion resistance and strong metallic bonding
The most common use of transition metals is in alloys. They are mixed together with other metals to make a stronger material. They also resist corrosion. Transition’s metals constitute a different kind of periodic elements from those in the main group. For example, their melting points and molar enthalpies of fusion are higher. In addition, they have strong metallic bonding and a delocalization of electrons that is different from that of main group elements.
4.3. Common oxidation states
Transition metals exhibit a variety of oxidation states. These states result from the removal of d-orbital electrons. The most common oxidation state of a transition metal is +2, and the lowest state is -4. Using a variety of oxidation states, transition metals can act as good heterogeneous and homogeneous catalysts in a variety of reactions.
4.3.1. Common examples
Some common examples include nickel in the production of margarine and platinum in the production of nitric acid. In both of these cases, the metal is able to change oxidation state in order to provide alternative routes that have a lower activation energy.
4.3.2. Tungsten
Tungsten has two common oxidation states: +2 and +6. This occurs when the ‘d’ orbitals of iron are half-filled. This oxidation state gives it an extra degree of stability. It is often used in cutting tools, dental drills, rock drills, and abrasives.
4.4. Common ionization enthalpy
When determining how challenging it is to strip electrons from a molecules, scientists often use the transitions metals’ shared ionization enthalpy. This enthalpy is dependent on the atomic number, and is dependent on the amount of electrons present in each atom. The removal of the electrons in a molecule becomes more difficult as the subshell becomes partially filled.
4.4.1. Calculation of IE
The ionization enthalpy (IE) of a metal can be calculated by computing the effective nuclear charge in each atom. Most transition metals exhibit multiple oxidation states separated by a single electron, such as the s-block element manganese. This fact makes most of their compounds paramagnetic.
4.4.2. Similarity in IE
Most transition metals have similar ionization enthalpies, resulting in the formation of similar charge metal ions. As a result, they have extensive similarities in chemistry. First-row transitions metals like lanthanides and actinides are highly susceptible to this effect. Most of these elements form stable compounds with a 2+ or 3+ charge.
4.5. Common melting point
The melting as well as heating values of transition metals are rather high. The percentage of their electrons that are unpaired is rather high. One aspect that determines the elements’ characteristics is the quantity of valence electrons they possess. The transitions metals are versatile because of their many beneficial features. They have excellent thermal and electrical conductivity, among other qualities. Their melting points are high, making them ideal for electrical and mechanical components. The vast majority of transitions metals are solids at normal temperatures. In addition to their high melting points, transition metals are hard, lustrous, and high density.
4.6. Other Common applications
Some common applications include building and construction materials, aerospace and automotive parts, and more. As an added bonus, they are also necessary for the creation of several metals and metal alloys. Numerous sectors rely on transition metals. For example, Nickel is used in electrical technology. Several of these metals have high melting points, and are therefore useful for making a variety of metallic alloys. Some are used in the manufacture of stained glass and are used as catalysts in chemical reactions. Others are used in industrial processes and are expected to play a role in curing diseases.
Conclusion
Transition metals are a class of elements with unique properties. They are also very hard and durable. Due to the features they already contain, they are ideal for use in the production of electronics as well as in other business contexts. They are found in many regions of the world, and several of them are mined commercially and have many applications in technology. For example, iron is a catalyst for the Haber reaction, a reaction between hydrogen and nitrogen that yields ammonia. Nickel and palladium are used in hydrogenation of alkenes and alkynes. Platinum is also used in automobile exhaust systems as a catalyst.
References
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2. Lèbre, É., Stringer, M., Svobodova, K., Owen, J. R., Kemp, D., Côte, C., … & Valenta, R. K. (2020). The social and environmental complexities of extracting energy transition metals. Nature communications, 11(1), 1-8.
3. Naeimi, A., Sharifi, A., Montazerghaem, L., Abhari, A. R., Mahmoodi, Z., Bakr, Z. H., … & Ali, G. A. (2022). Transition metals doped WO3 photocatalyst towards high efficiency decolourization of azo dye. Journal of Molecular Structure, 1250, 131800.