Transition Elements

Iron can form both Fe²⁺ and Fe³⁺ ions. Copper(II) sulfate makes a blue solution, while some transition metals and their compounds speed up reactions. These observations show different properties: learn to connect each piece of evidence to the claim it supports.

Where to find typical transition elements

Transition elements such as iron and copper are metals in the central block of the Periodic Table, between Groups 2 and 13. This course compares their typical properties. A position in the central block is a useful guide, but it does not mean that every element there shows every property below.

Physical properties: compare with Group 1 metals

Typical transition metals conduct heat and electricity and are malleable and ductile. Compared with lithium, sodium and potassium, they are generally harder, denser and higher-melting.

High melting point and high density are separate physical properties. These are general comparisons, not guarantees about every metal or alloy.

The same element can have different oxidation states

Iron forms two common ions:

• Fe²⁺: iron(II), oxidation state + 2;
• Fe³⁺: iron(III), oxidation state + 3.

The two charges demonstrate variable oxidation states. Both ions are iron: they have the same proton number. The Roman numeral records the oxidation state, not a number of atoms.

For a monatomic ion, oxidation state equals the ion charge. For an atom within a compound or a polyatomic ion, use the separate oxidation-state rules. Do not read an oxidation state as a total electron count.

Coloured compounds: name the substance and its state

Many transition-metal compounds are coloured. Familiar aqueous examples include:

Colour depends on the particular compound and conditions, not just the name of the metal. Anhydrous copper(II) sulfate is white, while hydrated copper(II) sulfate is blue. A white compound therefore does not rule out a transition element.

Potassium manganate(VII) contains potassium, a Group 1 metal, but its purple colour comes from the manganate(VII) ion containing manganese, a transition element. This is why “all Group 1 salts are white” is not a reliable rule. Sodium chloride and potassium chloride are familiar white salts whose solutions are colourless.

Catalysts: look for rate and recovery evidence

Transition elements and their compounds often act as catalysts. A catalyst increases reaction rate and is not consumed overall. For example, manganese(IV) oxide speeds up hydrogen peroxide decomposition and remains after the reaction.

Compare a reaction with and without the possible catalyst under otherwise comparable conditions. A faster reaction and recovery of the substance support catalyst behaviour. They do not prove by themselves that the substance is a transition-metal compound: other kinds of substance can also be catalysts.

For a reversible reaction at the same temperature, a catalyst does not change the equilibrium yield. It helps the reaction reach equilibrium faster. More product collected after a short fixed time can reflect a faster reaction rather than a changed equilibrium. See reversible reactions for that distinction.

Match evidence to the right property

One observation does not establish all the typical properties. In particular, colour alone is not a conclusive identification of an ion, and a compound need not catalyse every reaction.

State the property, then give its evidence

“Variable oxidation states, shown by Fe²⁺ and Fe³⁺” is stronger than writing two ion formulae without an explanation. For a catalyst, state both increases rate and not consumed overall. Keep high density and high melting point distinct if a question asks for physical properties.

Worked examples

Try these independently

Practise and check