Oxides and Transition Elements

Two shorter topics that appear together in questions about the Periodic Table: how an element’s position determines the character of its oxide, and what makes the transition metals different from Group I.

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Part 1: Oxides

The four types

BASIC oxides — METAL oxides. They react with ACIDS to form a salt and water. ACIDIC oxides — NON-METAL oxides. They react with BASES/ALKALIS to form a salt and water. AMPHOTERIC oxides — react with BOTH acids AND bases. NEUTRAL oxides — react with neither.

Metal oxide = basic; non-metal oxide = acidic. That single rule handles most questions, and it links directly to the trend across a period: oxides change from basic on the left to acidic on the right.

Basic oxides

Examples: Na₂O, MgO, CuO, CaO

metal oxide + acid → salt + water CuO + H₂SO₄ → CuSO₄ + H₂O

Soluble basic oxides (Group I and II) dissolve to form alkalis:

Na₂O + H₂O → 2NaOH

Acidic oxides

Examples: CO₂, SO₂, NO₂, SiO₂, P₄O₁₀

non-metal oxide + alkali → salt + water CO₂ + 2NaOH → Na₂CO₃ + H₂O

Soluble acidic oxides dissolve in water to form acids:

SO₂ + H₂O → H₂SO₃ (sulfurous acid) — this is the origin of acid rain

Amphoteric oxides

The ones to learn: ALUMINIUM OXIDE (Al₂O₃) and ZINC OXIDE (ZnO).

They react both ways:

With acid: Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O With alkali: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

“Amphoteric” means reacting with both acids and bases. Aluminium and zinc are the two you need — and note this is the same pair whose hydroxides dissolve in excess NaOH in the cation tests. The same amphoteric character explains both.

Neutral oxides

Examples: water (H₂O), carbon monoxide (CO), nitrogen monoxide (NO).

They react with neither acids nor bases.

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Part 2: Transition elements

Where they are

The transition elements occupy the middle block of the Periodic Table, between Groups II and III.

Common examples: iron, copper, zinc, nickel, chromium, manganese, silver.

Their properties

Transition elements are typical metals, but with four distinctive extra properties:

1. They form COLOURED compounds 2. They have VARIABLE OXIDATION STATES 3. They (and their compounds) act as CATALYSTS 4. They have HIGH densities, HIGH melting points and are HARD and STRONG

These four are the standard exam answer — a recorded error offered “have low densities” when the expected answer was “form coloured compounds”. Learn all four.

Coloured compounds

Ion	Colour in solution
Cu²⁺	blue
Fe²⁺	pale green
Fe³⁺	yellow-brown
Cr³⁺	green
Mn²⁺	pale pink

Contrast with Group I compounds, which are WHITE and dissolve to give COLOURLESS solutions.

Variable oxidation states

The same element can form more than one ion — which is why Roman numerals appear in the names.

• Iron(II), Fe²⁺ and iron(III), Fe³⁺
• Copper(I), Cu⁺ and copper(II), Cu²⁺

The Roman numeral IS the oxidation state. Uncertainty about the oxidation states of transition metals was recorded — read the numeral and you have the charge.

As catalysts

Catalyst	Process
Iron	Haber process (ammonia)
Vanadium(V) oxide	Contact process (sulfuric acid)
Nickel	hydrogenation of alkenes
Platinum	catalytic converters

Catalysts speed up reactions without being used up, by providing a route of lower activation energy.

Comparing with Group I

	Group I metals	Transition metals
Density	low	high
Melting point	low	high
Hardness	soft	hard, strong
Reactivity	very reactive	less reactive
Compounds	white/colourless	coloured
Oxidation states	only 1+	variable
Catalysts?	no	yes

Both are metals, so both conduct electricity and heat, are malleable, and form positive ions. A recorded question asked what is true of both sodium and iron — the answer is the general metallic properties, not the transition-specific ones.

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Mistakes that cost marks

Saying a non-metal oxide is basic (or the reverse).

Forgetting aluminium and zinc oxides are amphoteric.

Not knowing what “amphoteric” means.

Giving only one or two transition metal properties.

Saying transition metals have low densities.

Forgetting the Roman numeral in a transition metal name.

Confusing the ion colours.

Saying Group I compounds are coloured.

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Frequently asked questions

What kind of oxide does a metal form? A basic oxide.

What kind does a non-metal form? An acidic oxide.

What is an amphoteric oxide? One that reacts with both acids and bases — aluminium oxide and zinc oxide.

Give two neutral oxides. Water and carbon monoxide.

What does a basic oxide do with acid? Forms a salt and water.

Where are the transition elements? The middle block, between Groups II and III.

What are their four special properties? Coloured compounds, variable oxidation states, act as catalysts, and high density, melting point and hardness.

What colour is Fe³⁺ in solution? Yellow-brown. Fe²⁺ is pale green.

What does the Roman numeral mean? The oxidation state (charge) of the metal ion.

How do transition metals compare with Group I? They are harder, denser, higher melting and less reactive, with coloured compounds.

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Quick revision checklist

• I know metal oxides are basic and non-metal oxides acidic
• I can write the reactions of each with acid or alkali
• I know the amphoteric oxides are Al₂O₃ and ZnO
• I can name neutral oxides
• I know the oxide trend across a period
• I know where the transition elements sit
• I can give all four distinctive properties
• I know the common ion colours
• I understand variable oxidation states and Roman numerals
• I can name transition metal catalysts and their processes
• I can compare them with Group I

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These notes cover oxides and the transition elements in the Cambridge IGCSE Chemistry (0620) syllabus and are written for Grade 9–11 / Year 10–11 students. They are based on teaching patterns observed across a large set of one-to-one IGCSE Chemistry lessons. Both were among the less-covered subtopics in that set, so they are combined here and follow the syllabus closely rather than being padded. Always check the current syllabus for your own exam series.