Transition metals (AQA GCSE Chemistry): Revision Notes
Transition metals
What are transition metals?
Transition metals are a group of metals found in the middle of the periodic table. They sit between Groups 2 and 3, occupying a central position that gives them their unique properties.
The main transition metals you need to know are:
- Chromium (Cr)
- Manganese (Mn)
- Iron (Fe)
- Cobalt (Co)
- Nickel (Ni)
- Copper (Cu)
These metals are essential for understanding transition metal chemistry and appear frequently in chemical equations and reactions.
Key properties of transition metals
Transition metals have very different properties compared to Group 1 metals (like sodium). Understanding these differences is crucial for predicting their behaviour in chemical reactions and applications.
Physical properties:
- Higher density - they are much heavier than Group 1 metals
- Higher melting and boiling points - they need more heat to melt or boil (except mercury, which is liquid at room temperature)
- Stronger and harder - they don't bend or break as easily
Chemical properties:
- Much less reactive - they don't react as quickly with water, oxygen and halogens compared to Group 1 metals
The less reactive nature of transition metals is what makes them so useful in everyday applications. Unlike Group 1 metals that react violently with water, transition metals can be safely used in construction, tools, and jewellery without dangerous reactions.
Special features of transition metals
Transition metals have three important characteristics that make them very useful in both industrial and laboratory settings:
1. They form coloured compounds
Unlike Group 1 metals that form white or colourless compounds, transition metals create compounds with bright colours. This property is due to the way electrons behave in their partially filled d-orbitals.
Example: Copper Compounds
Copper forms copper(II) sulphate, which is bright blue in solution. This distinctive colour makes it easy to identify copper compounds in the laboratory.
2. They work as catalysts
Catalysts are substances that speed up chemical reactions without being used up themselves. Many transition metals can do this job very well because of their ability to provide alternative reaction pathways with lower activation energy.
3. They form different types of ions
Most metals form just one type of ion, but transition metals are different. They can form more than one type of ion with different charges, making them versatile in compound formation.
Example: Iron Ion Formation
Iron can form two different ions:
- Iron(II) ions: Fe²⁺
- Iron(III) ions: Fe³⁺
This ability to form multiple oxidation states allows iron to participate in many different types of chemical reactions.
Working with transition metal compounds
When transition metals form compounds, you need to be careful about working out the formulas. The key is to balance the total positive and negative charges to ensure the compound is electrically neutral.
Worked Example: Iron Oxide Formula
For iron oxide (Fe₂O₃):
Step 1: Identify the ions present
- The compound contains Fe³⁺ ions and O²⁻ ions
Step 2: Calculate total negative charge
- There are three oxide ions in Fe₂O₃
- Total charge from oxide ions: 3 × (-2) = -6
Step 3: Balance with positive charges
- To balance this, you need two Fe³⁺ ions
- Total positive charge: 2 × (+3) = +6
Result: The charges balance perfectly: +6 + (-6) = 0
Why transition metals are useful
Transition metals are incredibly important in modern society because of their unique combination of properties. Their versatility makes them essential across numerous industries and applications.
- Strong and hard - perfect for making tools and buildings
- High melting points - good for things that get very hot
- Catalysts - help make chemicals and medicines
- Coloured compounds - used in paints and dyes
- Less reactive - don't rust or corrode as quickly as other metals
Key Points to Remember:
- Transition metals are found between Groups 2 and 3 in the periodic table
- They are much stronger, harder and less reactive than Group 1 metals
- They form coloured compounds (unlike Group 1 metals which are white/colourless)
- They can work as catalysts to speed up reactions
- They can form more than one type of ion (like Fe²⁺ and Fe³⁺)