Properties of Transition Metals
Transition metals are a group of elements distinguished by three key chemical properties: their ability to form stable ions with different positive charges, their tendency to form brightly coloured compounds, and their widespread use as catalysts.
Part of the ESAT Chemistry syllabus — revision for the Engineering and Science Admissions Test (ESAT), the UAT-UK admissions test for Cambridge, Imperial, Oxford and UCL.
Key points
- Transition metals can form multiple stable ions, each with a different positive charge. This is known as having variable oxidation states. For example, iron can exist as both Fe2+ (iron(II)) and Fe3+ (iron(III)).
- Many compounds containing transition metal ions are coloured. This is a distinctive feature, contrasting with Group 1 and 2 metal compounds which are typically white. For example, copper(II) sulfate is blue, while potassium permanganate is deep purple.
- These metals and their compounds are excellent catalysts, meaning they increase the rate of chemical reactions without being used up. This applies to both the solid metal element and its ions in solution.
- Common examples of transition metal catalysts include iron in the Haber process for making ammonia, and nickel in the hydrogenation of alkenes to make alkanes.
Definitions
- Transition Metal
- An element from the d-block of the periodic table which can form at least one stable ion with an incomplete d-subshell.
- Oxidation State
- A number representing the degree of electron loss of an atom in a compound. For a simple ion, it is equivalent to its charge.
- Catalyst
- A substance that increases the rate of a chemical reaction but is not consumed by the reaction, meaning it can be recovered chemically unchanged at the end.
Worked example
An element, X, is a solid metal at room temperature. It reacts with chlorine to form two different compounds, a green solid with the formula XCl2 and a brown solid with the formula XCl3. An aqueous solution of XCl2 is also observed to accelerate the breakdown of a chemical reagent. Which category of element does X most likely belong to?
- 1
Identify the evidence provided.
The element X forms two distinct compounds with chlorine:
XCl2 and XCl3.
- 2
Interpret this first piece of evidence.
The existence of both XCl2 and XCl3 implies that element X can form stable ions with +2 and +3 charges.
This property is known as having variable oxidation states.
- 3
Analyse the second piece of evidence.
The compounds are described as 'green' and 'brown'.
The formation of coloured compounds is a characteristic property.
- 4
Analyse the third piece of evidence.
An aqueous solution containing ions of X acts as a catalyst ('accelerate the breakdown').
Catalytic activity is another key property.
- 5
Synthesise all three findings:
variable oxidation states, coloured compounds, and catalytic activity.
These are the defining characteristics of transition metals.
- 6
Conclude that element X is a transition metal.
Answer: Transition metal
Common mistakes
- ×Assuming all transition metal compounds are coloured. Compounds of zinc (Zn2+) or scandium (Sc3+) are notable exceptions and are typically colourless or white.
- ×Confusing the properties of transition metals with alkali metals (Group 1). Alkali metals are more reactive, only form +1 ions, and their compounds are almost always white.
- ×Forgetting that both the neutral metal atoms (e.g., a nickel surface) and their dissolved ions (e.g., Fe2+(aq)) can act as catalysts.
No-calculator tips
- ✓In a question, the mention of a coloured solution (blue, green, purple, yellow) involving a metal compound is a very strong hint that a transition metal is present.
- ✓If you see a metal forming compounds with different formulae (e.g., FeCl2 and FeCl3), immediately recognise this as variable oxidation states, a hallmark of transition metals.
- ✓Mentally link a specific, common example to each property: Iron for variable states (Fe2+/Fe3+), Copper for colour (blue CuSO4), and Nickel for catalysis (hydrogenation).