Important Groups
4. Transition Metals
Learning outcomes
- I can identify transition metals on the periodic table.
- I can compare the properties of transition metals with those of Group 1 metals.
- I can describe common physical properties of transition metals.
- I can explain why many transition metals have multiple oxidation states and form colored compounds.
- I can identify important applications of transition metals in industry and technology.
What Are Transition Metals?
The transition metals are metallic elements found in the central region of the periodic table.
They are associated with the d-block, which lies between the main-group metals on the left and the non-metals toward the right.
Familiar examples include:
- titanium (Ti)
- chromium (Cr)
- manganese (Mn)
- iron (Fe)
- cobalt (Co)
- nickel (Ni)
- copper (Cu)
Other transition metals include elements such as zirconium, molybdenum, silver, tungsten, platinum, and gold.
Transition metals are especially important because they combine useful physical properties with interesting chemical behaviour.
Where Are Transition Metals Found?
Transition metals occupy the large block in the middle of the periodic table.
This region is called the d-block because electrons are being added to d orbitals as we move through it.
In introductory chemistry, the terms "d-block elements" and "transition metals" are sometimes used almost interchangeably.
There is, however, a more precise distinction.
A More Precise Definition
A transition element is commonly defined as an element that forms at least one stable ion with a partially filled d subshell.
This means that not every element in the d-block behaves as a transition element under the strict definition.
For example, zinc is located in the d-block but Zn²⁺ has a completely filled d subshell.
For introductory work, the most important idea is that transition metals occupy the central metallic region of the periodic table and share several characteristic properties.
Common Physical Properties
Transition metals generally have the physical properties we associate with metals.
They are usually:
- strong
- hard
- dense
- shiny when polished
- malleable
- ductile
- good electrical conductors
- good thermal conductors
- relatively high in melting point
These properties make transition metals extremely useful engineering materials.
Strength and Hardness
Many transition metals are significantly harder and stronger than Group 1 metals.
Iron, titanium, chromium, and nickel are important examples.
Their strength allows them to be used in:
- buildings
- bridges
- vehicles
- machinery
- tools
- aircraft
- industrial equipment
Their exact properties vary considerably from one transition metal to another.
High Density
Transition metals tend to have relatively high densities.
For example, iron, copper, nickel, and silver are considerably denser than Group 1 metals such as lithium, sodium, and potassium.
This is one major physical difference between transition metals and alkali metals.
High Melting Points
Most transition metals have relatively high melting points.
This makes many of them suitable for applications involving:
- high temperatures
- engines
- machinery
- industrial equipment
- structural materials
Tungsten is particularly notable for its extremely high melting point.
There are exceptions to the general trend. Mercury, for example, is a liquid at room temperature.
Good Electrical Conductors
Transition metals conduct electricity effectively.
Copper is one of the most familiar examples.
Copper is widely used for electrical wiring because it combines:
- high electrical conductivity
- ductility
- useful mechanical properties
Silver is an even better electrical conductor, but its cost limits its use for ordinary wiring.
Good Thermal Conductors
Transition metals are also good conductors of thermal energy.
Copper is commonly used where rapid heat transfer is useful.
Applications include:
- cookware
- heat exchangers
- cooling systems
- electronic components
The ability to conduct both heat and electricity is characteristic of metallic bonding.
Transition Metals vs Group 1 Metals
Both transition metals and Group 1 elements are metals.
However, their properties can be very different.
Group 1 metals are generally:
- very soft
- relatively low in density
- relatively low in melting point
- highly reactive
- likely to form only +1 ions in simple compounds
- less commonly used as structural materials in their pure form
Transition metals are generally:
- harder
- stronger
- denser
- higher melting
- less reactive
- capable of multiple oxidation states
- useful as catalysts
- able to form many coloured compounds
These differences are important when selecting materials for practical applications.
Comparing Reactivity
Group 1 metals are extremely reactive.
For example, sodium and potassium react rapidly with water.
Transition metals are generally less reactive.
Copper, for example, does not react vigorously with cold water.
Gold and platinum are particularly resistant to chemical reaction.
This lower reactivity makes some transition metals useful where resistance to corrosion is important.
Transition Metals and Ions
Like other metals, transition metals can lose electrons and form positive ions.
However, unlike Group 1 metals, many transition metals can form ions with different charges.
For example, iron commonly forms:
Fe²⁺
and:
Fe³⁺
Copper commonly forms:
Cu⁺
and:
Cu²⁺
This behaviour is called having variable oxidation states.
What Is an Oxidation State?
An oxidation state is a way of keeping track of how electrons are distributed in compounds and ions.
For simple monatomic ions, the oxidation state corresponds directly to the ion's charge.
For example:
Fe²⁺ → iron has oxidation state +2
Fe³⁺ → iron has oxidation state +3
Cu²⁺ → copper has oxidation state +2
Transition metals are unusual because several oxidation states may be chemically accessible.
Why Can Transition Metals Have Multiple Oxidation States?
Transition metals involve electrons in the outer s orbitals and nearby d orbitals.
The energies of these electrons can be relatively similar.
As a result, different numbers of electrons can participate in bonding or be removed during reactions.
This allows many transition metals to form ions with different charges.
For example:
Iron can lose electrons to form:
Fe²⁺
or:
Fe³⁺
Manganese can occur in several different oxidation states depending on the compound.
Group 1 Is Different
Sodium has the electron arrangement:
2,8,1
It very readily loses its one outer electron:
Na → Na⁺ + e⁻
Removing another electron would require removing one from a stable inner shell.
Therefore, sodium overwhelmingly forms:
Na⁺
Transition metals do not have such a simple separation between the energies of their outer s and nearby d electrons.
This contributes to their variable oxidation states.
Naming Transition Metal Compounds
Because transition metals can have different oxidation states, the metal's oxidation state often needs to be included in the compound's name.
For example:
FeCl₂
is:
iron(II) chloride
because iron is Fe²⁺.
FeCl₃
is:
iron(III) chloride
because iron is Fe³⁺.
The Roman numeral tells us the oxidation state of the metal.
Another Example: Copper
Consider:
CuCl
Chloride has a charge of −1.
Therefore, copper must be +1.
The compound is:
copper(I) chloride
Now consider:
CuCl₂
Two Cl⁻ ions give a total charge of −2.
Therefore, copper must be +2.
The compound is:
copper(II) chloride
This shows why oxidation states are important when naming transition-metal compounds.
Coloured Compounds
One of the most distinctive chemical properties of transition metals is that many of their compounds are coloured.
For example, compounds containing different transition-metal ions may appear:
- blue
- green
- yellow
- orange
- purple
- pink
- brown
The exact colour depends on the metal ion, oxidation state, surrounding ions or molecules, and chemical environment.
Examples of Coloured Transition-Metal Compounds
Common classroom examples include:
Cu²⁺ compounds
Often blue or blue-green in aqueous environments.
Fe²⁺ compounds
Often pale green in aqueous solution.
Fe³⁺ compounds
Often yellow, orange, or brown depending on the species present.
Ni²⁺ compounds
Often green.
Co²⁺ compounds
Can show pink or blue colours depending strongly on their chemical environment.
These are general descriptions. Transition-metal colours can change significantly depending on which ligands surround the metal ion.
Why Are Many Transition-Metal Compounds Coloured?
The colours are connected to the d electrons of transition-metal ions.
When ligands or other particles surround a transition-metal ion, interactions with the ion cause the d orbitals to have different energies.
Electrons can absorb particular wavelengths of visible light and move between these energy levels.
The remaining transmitted or reflected light produces the colour that we observe.
Therefore:
d-electron structure → selective absorption of visible light → observed colour
This is a simplified introduction to crystal field and ligand field ideas.
Why Oxidation State Can Affect Colour
Changing the oxidation state changes the number and arrangement of d electrons.
This can change which wavelengths of light are absorbed.
Therefore, different oxidation states of the same transition metal can produce compounds with different colours.
This is one reason transition-metal chemistry can be visually distinctive.
Transition Metals as Catalysts
Many transition metals and their compounds are excellent catalysts.
A catalyst increases the rate of a chemical reaction without being consumed overall.
Transition metals can be effective catalysts partly because they can:
- change oxidation state
- interact with reactant molecules
- provide surfaces where reactions occur
- form temporary intermediate species
Iron and the Haber Process
Iron is used as a catalyst in the industrial production of ammonia.
The process is called the Haber process.
The overall reaction is:
N₂ + 3H₂ ⇌ 2NH₃
Ammonia is extremely important in the production of nitrogen fertilizers.
This makes iron's catalytic properties important to global agriculture.
Nickel as a Catalyst
Nickel can be used as a catalyst in hydrogenation reactions.
Hydrogenation involves adding hydrogen to unsaturated compounds.
Nickel provides a surface where reactant particles can adsorb and react more readily.
This is another example of transition metals having important industrial roles because of their catalytic properties.
Platinum, Palladium, and Rhodium
Platinum-group metals are important catalysts.
One familiar application is the catalytic converter in vehicle exhaust systems.
Catalytic converters help convert some harmful exhaust pollutants into less harmful substances.
Metals used in these systems can include:
- platinum
- palladium
- rhodium
Their catalytic activity makes them valuable despite their high cost.
Iron and Steel
Iron is one of the world's most important transition metals.
Pure iron has useful properties, but enormous quantities of iron are used in steel.
Steel is an alloy based mainly on iron.
Steel is used in:
- buildings
- bridges
- vehicles
- tools
- machinery
- railways
- ships
- pipelines
Different alloy compositions allow engineers to modify properties such as strength, hardness, and corrosion resistance.
What Is an Alloy?
An alloy is a mixture containing a metal and one or more other elements.
Transition metals are commonly used in alloys because their properties can be adjusted for particular applications.
Different-sized atoms can disrupt the regular arrangement of metal atoms and make it more difficult for layers to slide.
This can make an alloy harder or stronger than a pure metal.
Stainless Steel
Stainless steel is an important iron-based alloy.
It commonly contains chromium and may also contain nickel and other elements.
Chromium greatly improves corrosion resistance by helping form a thin protective oxide layer at the surface.
Stainless steel is used in:
- kitchen equipment
- medical instruments
- buildings
- industrial equipment
- food-processing equipment
Chromium
Chromium is useful because of properties including:
- hardness
- corrosion resistance
- ability to form useful alloys
- distinctive compounds
It is an important component of stainless steel.
Chromium compounds also demonstrate the colourful chemistry characteristic of transition elements.
Nickel
Nickel is important in:
- alloys
- stainless steels
- catalysts
- batteries
- high-temperature materials
Nickel-containing alloys can retain useful mechanical properties under demanding conditions.
This makes nickel valuable in engineering and energy technologies.
Copper
Copper combines excellent electrical conductivity with high ductility.
It can therefore be drawn into thin wires while still conducting electricity effectively.
Copper is widely used in:
- electrical wiring
- motors
- generators
- electronics
- plumbing
- heat exchangers
Copper also forms important alloys such as bronze and brass.
Titanium
Titanium is especially useful because it combines:
- high strength
- relatively low density for a strong structural metal
- excellent corrosion resistance
Titanium and its alloys are used in:
- aircraft
- spacecraft
- high-performance engineering
- medical implants
- chemical-processing equipment
Its properties make it valuable where both strength and relatively low mass are important.
Tungsten
Tungsten is notable for its extremely high melting point.
It also has high density and useful mechanical properties.
Tungsten and tungsten-containing materials are used in applications involving:
- high temperatures
- electrical contacts
- electrodes
- cutting and drilling materials
Tungsten carbide is especially important in very hard cutting tools.
Silver
Silver has extremely high electrical conductivity.
It is also lustrous and relatively resistant to many forms of corrosion.
Applications include:
- electrical contacts
- electronics
- jewellery
- mirrors and coatings
- specialized conductive materials
Its high cost means that cheaper metals such as copper are more commonly used when large quantities of conductor are required.
Gold
Gold is another familiar transition metal.
Gold is:
- highly malleable
- highly ductile
- electrically conductive
- very resistant to corrosion
These properties make it useful not only for jewellery but also for specialized electrical contacts and electronic components.
Transition Metals in Biological Systems
Transition metals are also important in living organisms.
For example, iron is an essential part of haemoglobin, the protein involved in oxygen transport in blood.
Other transition-metal ions are found in enzymes and other biological molecules.
Their ability to change oxidation state can make them especially useful in biological electron-transfer reactions.
Multiple Oxidation States and Redox Reactions
Because many transition metals can exist in several oxidation states, they are important in redox chemistry.
For example:
Fe²⁺ → Fe³⁺ + e⁻
Iron changes from oxidation state +2 to +3.
The reverse process is:
Fe³⁺ + e⁻ → Fe²⁺
The ability to move between oxidation states helps explain why transition-metal ions are involved in many catalytic, biological, and electrochemical processes.
Predicting Whether an Element Is a Transition Metal
Suppose you are given an unfamiliar element on a periodic table.
Ask:
Where is it located?
If it lies in the central d-block, it may be a transition metal.
Then look for characteristic behaviour such as:
- variable oxidation states
- coloured compounds
- catalytic activity
- high density
- relatively high melting point
Not every transition metal displays every characteristic equally strongly, but these patterns are useful.
Worked Example 1: Comparing Sodium and Iron
Compare sodium and iron.
Sodium:
- Group 1
- soft
- low density
- relatively low melting point
- highly reactive
- normally forms Na⁺
Iron:
- transition metal
- much stronger and harder
- higher density
- much higher melting point
- less reactive
- commonly forms Fe²⁺ and Fe³⁺
Therefore, iron displays many characteristic transition-metal properties.
Worked Example 2: Oxidation State
Determine the oxidation state of iron in:
FeCl₃
Each chloride ion has charge:
−1
Three chloride ions give:
−3
The compound is neutral.
Therefore, iron must be:
+3
The compound is:
iron(III) chloride
Worked Example 3: Copper Compound
Determine the oxidation state of copper in:
CuO
Oxygen normally has oxidation state:
−2
The compound is neutral.
Therefore:
Cu = +2
The compound is:
copper(II) oxide
Worked Example 4: Industrial Application
Why is copper used extensively for electrical wiring?
Copper has:
- excellent electrical conductivity
- high ductility
Therefore, copper can carry electrical current efficiently and can be drawn into long, thin wires.
This is a good example of connecting:
property → application
Worked Example 5: Catalyst
Why are transition metals often useful as catalysts?
Many transition metals can:
- adopt different oxidation states
- interact with reactant molecules
- form temporary intermediate species
- provide surfaces for reactions
These properties can provide alternative reaction pathways with lower activation energies.
Therefore, many transition metals and their compounds are effective catalysts.
Connecting Properties to Applications
A useful way to understand transition metals is to avoid simply memorizing uses.
Instead, connect the application to a physical or chemical property.
Copper
High electrical conductivity → wiring.
Titanium
High strength + relatively low density → aircraft.
Chromium
Corrosion resistance → stainless steel.
Iron
Strength + alloy formation → construction.
Nickel
High-temperature alloy properties → engineering.
Platinum
Catalytic activity → catalytic converters and industrial catalysts.
This approach makes applications easier to understand and remember.
Common Mistakes
Mistake 1: Thinking transition metals are located on the far left
Transition metals occupy the central d-block of the periodic table.
Mistake 2: Assuming all metals have properties similar to Group 1
Group 1 metals are unusually soft and reactive.
Transition metals are generally harder, stronger, denser, and less reactive.
Mistake 3: Assuming every transition metal forms only one ion
Many transition metals have multiple oxidation states.
For example:
Fe²⁺ and Fe³⁺
Mistake 4: Forgetting Roman numerals
In names such as:
iron(III) chloride
the Roman numeral indicates the oxidation state of the metal.
Mistake 5: Saying every transition-metal compound has the same colour
Colour depends on factors including:
- metal
- oxidation state
- surrounding ligands
- chemical environment
Mistake 6: Saying catalysts increase the amount of product that can theoretically form at equilibrium
A catalyst primarily increases the rate at which equilibrium is reached by providing a lower-activation-energy pathway. It does not change the equilibrium position.
Did You Know?
Transition metals have been central to human technological development for thousands of years.
Copper was one of the earliest metals widely used by humans.
Mixing copper with tin produced bronze, an alloy harder than pure copper.
Later, increasingly sophisticated iron production helped transform tools, weapons, agriculture, construction, and transportation.
Modern technology continues to depend heavily on transition metals in electronics, energy systems, transportation, medicine, and advanced materials.
Key Terms
Transition metal: A metal associated with the d-block that, under the strict definition, forms at least one ion with a partially filled d subshell.
d-block: The central region of the periodic table associated with filling d orbitals.
Oxidation state: A value representing the formal distribution of electrons in a compound or ion.
Variable oxidation state: The ability of an element to occur in more than one oxidation state.
Catalyst: A substance that increases reaction rate without being consumed overall.
Coloured compound: A compound that selectively absorbs some wavelengths of visible light and therefore appears coloured.
Alloy: A mixture containing a metal and one or more other elements.
Ductile: Able to be drawn into wires.
Malleable: Able to be hammered or shaped without breaking.
Redox reaction: A reaction involving oxidation and reduction.
Ligand: An ion or molecule that bonds to a central metal ion in a complex.
Key Patterns
Transition metals are generally:
harder than Group 1 metals
stronger than Group 1 metals
denser than Group 1 metals
higher melting than Group 1 metals
less reactive than Group 1 metals
Many transition metals also:
have variable oxidation states
form coloured compounds
act as catalysts
form useful alloys
conduct heat and electricity
Key Takeaways
- Transition metals occupy the central d-block of the periodic table.
- Familiar examples include iron, copper, nickel, chromium, manganese, cobalt, and titanium.
- Transition metals generally have typical metallic properties, including good electrical and thermal conductivity.
- Compared with Group 1 metals, they are generally harder, stronger, denser, higher-melting, and less reactive.
- Group 1 metals usually form +1 ions, while many transition metals can form ions with different oxidation states.
- Iron commonly forms Fe²⁺ and Fe³⁺.
- Copper commonly forms Cu⁺ and Cu²⁺.
- Variable oxidation states arise because outer s electrons and nearby d electrons can have relatively similar energies.
- Roman numerals in compound names indicate the oxidation state of a metal, such as iron(II) and iron(III).
- Many transition-metal compounds are coloured.
- Their colours are connected to the behaviour of electrons in partially filled d orbitals and the surrounding chemical environment.
- Many transition metals are effective catalysts.
- Iron is important in steel and is used as a catalyst in ammonia production.
- Copper's conductivity and ductility make it important for electrical wiring.
- Titanium's strength, corrosion resistance, and relatively low density make it useful in aerospace and medical applications.
- Chromium and nickel are important components of many alloys.
- Platinum-group metals are important industrial and automotive catalysts.
- Transition metals are essential to modern construction, transportation, electronics, energy, medicine, and manufacturing.
- Their applications can be understood by connecting atomic structure → chemical and physical properties → technological uses.