In this explainer, we will learn how to describe the compounds and reactivities of transition metals and trends in their physical and chemical properties.
Most elements on the periodic table are metals. There are only a handful of elements that are metalloids and nonmetals.
The elements are placed in specific groupings or families on the periodic table because they react in a similar manner. For example, the metals in group 1 have similar chemical properties and they are grouped together and called the alkali metals. The metals in group 2 behave in a similar manner to each other and are collectively called the alkaline earth metals. The metals in groups 3 to 12 are collectively called the d-block elements, outlined in red in the periodic table below.
Older naming conventions for the vertical columns of the periodic table’s d-block use IIIB, IVB, VB, VIB, VIIB, VIIIB, IB, and IIB as can be seen in the section of the periodic table shown below. VIIIB covers three groups (8, 9, and 10).
The d-block elements are sometimes loosely referred to as the transition metals. However, not all d-block elements are transition metals according to the International Union of Pure and Applied Chemistry (IUPAC). The IUPAC definition of a transition metal is an element whose atoms have an incomplete d subshell or that can give rise to cations with an incomplete d subshell.
Definition: Transition Metal
A transition metal is an element whose atoms have an incomplete d subshell or that can give rise to cations with an incomplete d subshell.
The elements in group 12, zinc (), cadmium (), mercury (), and copernicium (), have complete d subshells and so are not generally considered transition metals.
The periodic table above shows, in orange, which elements are considered to be transition elements according to the IUPAC definition. The elements in the lanthanide and actinide series, the f-block elements, are also transition elements and are known as the inner transition metals.
Example 1: Identifying Which Element Is Not a Transition Element
Which of the following is not a transition metal?
- Cobalt
- Rhodium
- Zirconium
- Potassium
- Gold
Answer
A transition metal is any element which has an incomplete d subshell or which can form cations with an incomplete d subshell. These elements are shown in orange below.
Of the possible answer options, only potassium does not have d electrons or an incomplete d subshell. Potassium is located in the s block and so its valence electrons are in an s subshell. The correct answer is D: potassium.
The elements found in period 4 of the d block are known as the first transition series. The elements found in period 5 are known as the second transition series, and those in the 6th period are known as the third transition series.
Let us investigate some of the physical properties of the transition metals.
Like all metals, the transition metals are malleable and can be hammered into flat sheets. They are also ductile and can be pulled into thin wires. The transition metals contain the most malleable and ductile elements, namely, gold, silver, and platinum.
Another physical property of the transition metals that is noticeably different from other metals is the melting point. The graph below shows the melting points of some s-block metals and the transition metals in period 4, as well as the melting point of tungsten.
The graph shows that the melting points of the transition metals are, in general, higher than the melting points of the s-block metals. Tungsten, in period 6, is also a transition metal. It has the highest melting point of all pure metals, .
Example 2: Understanding Melting Point Trends for Transition Metals versus Main-Group Elements
Shown in the graph are the melting points of the first 56 elements of the periodic table and the groups in which they occur.
The transition metals are positioned between groups 3 and 11. Which of the following is the most accurate comparison of the melting points shown in the graph?
- The transition metals and main-group elements display a similar range of melting points.
- The transition metals have lower melting points than almost all of the main-group elements.
- The transition metals have lower melting points than all of the main-group elements.
- The transition metals have higher melting points than almost all of the main-group elements.
- The transition metals have higher melting points than all of the main-group elements.
Answer
The graph shows that elements in groups 3 to 11 generally have higher melting points than the elements in other groups. There are only a few red dots (melting points) positioned higher than those in groups 3 to 11. This tells us that some main-group elements have higher melting points than transition metals, but this is not the general trend. The statement that is the most accurate is statement D: the transition metals have higher melting points than almost all of the main-group elements.
Metals, in general, conduct heat and electricity well. The transition elements in group 11, specifically copper, silver, and gold, are particularly excellent conductors of electricity. Copper is the cheapest and most abundant of these metals and therefore is commonly used in electrical wiring. Some specialist devices use gold to conduct electricity instead of copper and, of the three metals, silver has the highest conductivity.
Hardness and strength are important physical properties in the manufacturing of metal components. Many transition metals are relatively hard compared with s-block metals, some of which are soft enough to cut with a knife. Most transition metals are also strong. For example, titanium has high strength. Transition metals are very useful in applications where strength or hardness is required.
High density is another property common to many transition metals. The graph below shows the relative densities, at room temperature, of some transition metals compared with several s-block metals.
The density of transition metals is generally much higher than the density of metals in the s-block. The two most dense metals of all metals are osmium and iridium, both transition metals, with densities of nearly 23 g/cm3.
The transition metals also show some obvious differences to other metals in terms of chemical properties. A noticeable difference is that most transition metals are able to form more than one stable oxidation state, while most main-group elements tend to have only one stable oxidation state, besides an oxidation state of zero which all elements exhibit in their pure form. For example, manganese has a variety of possible oxidation states that allows manganese to form a variety of compounds.
| Manganese Oxidation State | Example of an Associated Compound or Ion |
|---|---|
| , manganese(II) | |
| , manganese(III) | |
| , manganese(IV) oxide | |
| , manganese(V) | |
| , manganese(VI) | |
| , permanganate |
Transition metal ions can be converted between their different oxidation states by oxidizing or reducing them. The equation below shows how iron in the state can be oxidized to a state, and reduction will convert the ion back to the ion.
Typically, when a transition metal has a low oxidation state, it exists as an individual ion, for example, the ferrous or iron(II) ion exists as , and the ferric or iron(III) ion exists as . When a transition metal has a high oxidation state, it is usually bonded to another element such as oxygen in an oxide or polyatomic anion. Two instances of this occur with the element chromium, which can bond to oxygen when it has an oxidation state of , forming the chromate and the dichromate ions. This is shown in the following table.
| Ion Name | Ion Formula | Oxidation State | Comment | |
|---|---|---|---|---|
| Iron(II) ion | Low | Individual metal cation | ||
| Iron(III) ion | ||||
| Chromate ion | High | Metal ion is bonded to another element. | ||
| Dichromate ion | ||||
Example 3: Understanding That Transition Elements Have Several Stable Oxidation States
Which of the following statements explains why two versions of iron hydroxide, and , exist?
- Transition metals have high melting points.
- Transition metals form colored compounds.
- Transition metals are magnetic.
- Transition metals and their compounds make good catalysts.
- Transition metals can have more than one ion.
Answer
Transition metals can exist in more than one stable oxidation state; in other words, they can form different ions. Most main-group elements tend to form one ion or an ion with one charge value only. In , iron has a oxidation state, or is in the form, while in , iron has a oxidation state, or is in the form. The correct answer is E: transition metals can have more than one ion.
The oxidation state of an ion can influence the color of transition metal compounds, which have a wide variety of colors in their solid states and aqueous solutions. The table below shows the colors of some common ions of the first transition series in solution.
Example 4: Comparing the Properties of the Alkali Metals and Transition Metals
Transition metals and alkali metals have a few features in common but are different in many ways. Which of the following statements is false?
- Transition metals produce less colorful compounds than alkali metals.
- Alkali metals have lower melting and boiling points than transition metals.
- Alkali metals are not widely used as catalysts, while transition metals are.
- Transition metals are harder and stronger than alkali metals.
- Transition metals have a larger number of stable oxidation states than alkali metals.
Answer
The metallic elements in group 1 and the transition elements are all metals and so share many typical properties of metals. However, these two families of metals show some differences.
We are asked to decide which statement about properties is false.
The transition metals, in general, tend to melt and boil at much higher temperatures than the alkali metals. Statement B is true.
Transition metals make excellent catalysts, while alkali metals do not. Statement C is true.
Alkali metals are softer and not as strong as the transition metals. Statement D is true.
Alkali metals tend to form a oxidation state only, when bonding, while the transition metals can form several stable oxidation states. Statement E is true.
Many alkali metal compounds are white in color and are colorless in solution, while the transition metal compounds have a wide variety of colors in their solid states and aqueous solution. Statement A is false. So, the correct answer is A: transition metals produce less colorful compounds than alkali metals.
When in their pure metal form, the transition metals are relatively unreactive. For example, pure iron will react with water, and oxygen in the air, and will rust, but this process is slow compared to the reaction of some other elements with water or oxygen. Many other metals, such as the group 1 metals, are much more reactive. Lithium, in group 1, will fizz on water while potassium will react even more vigorously releasing much heat energy.
Most transition metals, when heated, react with oxygen in the air to form oxides. For example, titanium will react with oxygen under high temperature according to the following equation:
White titanium(IV) oxide, also known as titanium dioxide, is produced.
Silver, gold, platinum, palladium, rhodium, ruthenium, osmium, and iridium are called noble metals, because they are unreactive and stable under normal conditions, although silver will tarnish (turn black) slowly over time when exposed to oxygen. Noble metals are not oxidized easily and therefore do not corrode, nor do they react with most acids. The diagram below shows which elements are noble metals.
Definition: Noble Metals
Noble metals are metals that are highly resistant to chemical reaction.
Other transition metals do react with acids, although slowly compared to many other metals. Many of the first transition metal series react with acid according to this general equation:
For example, chromium reacts with hydrochloric acid to produce chromium(II) chloride and hydrogen gas:
The physical and chemical properties of transition metals directly influence their usefulness. Transition metals are very important socially and economically because of their many applications.
Titanium is commonly used in alloys, because of its durability, as well as in dental implants. The compound titanium dioxide () is used in sunscreen lotions, as shown below, where it helps protect the skin from the harmful effects of ultraviolet (UV) light.
The compound vanadium pentoxide () is a very important catalyst that is used in the contact process to produce sulfuric acid (). The figure below shows vanadium pentoxide microcrystals.
Chromium is often used in metal plating, for example, on motorcycle engine components, as shown below, or in car “fenders.” It is also used for leather tanning.
Iron is the main component of steel alloys, which are widely used in engineering. However, iron can also be used as a catalyst, most notably in the Haber–Bosch process for the manufacture of ammonia gas (). The images below show the use of iron as part of a steel girder and in the production of ammonia.
Copper is mainly used in electrical wiring, as shown below, but it is also the primary component of bronze alloys.
Example 5: Understanding an Application of Transition Metals
Which of the following statements explains why platinum, palladium, and rhodium are used in converters in car exhausts?
- Transition metals react slowly or not at all with acid.
- Transition metals make good catalysts.
- Transition metals are very dense.
- Transition metals have high melting points.
- Transition metals form colored compounds.
Answer
Transition metals have excellent catalytic activity and are widely used as catalysts for many processes. One of these processes is the catalytic conversion of toxic exhaust compounds, such as gases and , to less harmful compounds, such as , , and . Typically, platinum, palladium, and rhodium are used for this purpose. The correct answer is B: transition metals make good catalysts.
Key Points
- A transition metal is an element whose atoms have an incomplete d subshell or which can give rise to cations with an incomplete d subshell.
- Transition metals
- are malleable and ductile,
- in general, when compared to s-block metals, have higher
- melting points,
- densities,
- hardness,
- electrical conductivity,
- strength,
- can form several stable oxidation states and thus many compounds,
- form different colored ions,
- are generally less reactive than s-block elements,
- often have good catalytic activity.
