Chemistry 2e · Transition Metals and Coordination Chemistry
Occurrence, Preparation, and Properties of Transition Metals and Their Compounds
On this page 9 sections
In 30 seconds
Transition metals are the d-block elements of Groups 3–12, defined by a partially filled d subshell in the neutral atom or a common ion. That one feature generates the family's personality: multiple oxidation states, colored compounds, paramagnetism, catalytic activity, and a strong tendency to form complex ions (the next two topics). Because most are reactive, they occur in Earth's crust as ores — oxides, sulfides, carbonates — rather than as free metals; only the noble metals (gold, silver, platinum) occur native. Extracting a metal from its Ore Rock rich enough in a metal compound to mine and process economically Full entry → (metallurgy) always involves chemistry: concentrate, convert to a reducible form, reduce, purify. This topic covers occurrence, the three extraction routes (pyrometallurgy, Hydrometallurgy Extracting a metal by dissolving it from the ore in aqueous solution Full entry →, Electrometallurgy Using electrolysis to deposit or refine a metal Full entry →), the characteristic properties, and representative chemistry of iron, copper, chromium, and manganese.
Why this matters
- Materials: Steel (Fe + C), stainless steel (Fe + Cr), titanium alloys, copper wiring, tungsten filaments — the strongest, densest, hardest structural metals known.
- Catalysis: Iron catalyzes the Haber process (ammonia fertilizer); Pt, Pd, Rh power catalytic converters; nickel hydrogenates vegetable oils.
- Biology and medicine: Iron carries oxygen in hemoglobin; cobalt is the metal in vitamin B₁₂; platinum compounds are anticancer drugs.
- Exams: Oxidation-state determination, ore-to-metal chemistry, and the reactivity–extraction connection are high-frequency questions.
The college version
Core Concepts
Occurrence: ores and native metals
Iron is ~5% of Earth's crust (fourth most abundant element), but most transition metals are scarcer (titanium ~0.6%, manganese ~0.1%, chromium ~0.01%, copper ~0.007%). They occur combined in mineable ores: oxides — hematite (Fe₂O₃), magnetite (Fe₃O₄), rutile (TiO₂), chromite (FeCr₂O₄), pyrolusite (MnO₂); sulfides — chalcopyrite (CuFeS₂), zinc blende (ZnS); native — gold, silver, platinum-group metals, unreactive enough to survive uncombined. The extraction method a metal needs tracks its position in the activity series: the more reactive, the more energy the reduction step requires.
Pyrometallurgy: roasting and reduction with heat
Pyrometallurgy uses heat. Two classic steps:
- Roasting Heating a sulfide ore in air to convert it to the oxide a sulfide ore in air converts it to the oxide and drives off SO₂: 2ZnS + 3O2 → 2ZnO + 2SO2.
- Reduction with carbon or CO (Smelting Reducing a metal oxide with carbon or CO at high temperature Full entry →) frees the metal — in the blast furnace, coke burns to CO, which reduces hematite:
Fe2O3 + 3CO → 2Fe + 3CO2
Carbon works because it is cheap and regenerable. Metals too reactive for carbon need stronger reductants: titanium ore becomes TiCl₄, reduced by molten magnesium in the Kroll process:
TiCl4 + 2Mg → Ti + 2MgCl2
run near 1000 °C under argon because everything involved is oxygen-hungry at that temperature.
Hydrometallurgy: leaching in solution
Hydrometallurgy dissolves the metal out of the ore with aqueous reagents. The classic example is cyanide leaching of gold, which exploits the stable complex cyanide forms with Au⁺:
4Au + 8NaCN + O2 + 2H2O → 4Na[Au(CN)2] + 4NaOH
The dissolved gold is precipitated by adding zinc dust (zinc is more reactive and displaces gold). Copper is recovered from low-grade ores by acid leaching followed by electrolysis ("electrowinning").
Electrometallurgy and purification
The most reactive metals — those carbon or another metal cannot reduce — are won by electrolysis of molten salts or aqueous solutions. Purification often uses electrolytic refining: an impure copper anode dissolves and pure copper plates onto the cathode while impurities settle as anode mud (a commercial source of Au, Ag, Pt). Ultrapure metals are finished by Zone refining Passing a narrow molten zone along a rod to sweep impurities to one end Full entry →, where a narrow molten zone sweeps impurities to one end of a rod.
Properties of the metals and their compounds
- High melting points, densities, hardness — tungsten (mp 3422 °C, highest of any metal), osmium and iridium (~22.6 g/cm³, the densest elements), chromium (hardest metal) — because both s and d electrons contribute to metallic bonding.
- Variable oxidation states — the hallmark. The ns and (n-1)d electrons have similar energies, so different numbers can participate: Fe +2/+3, Cu +1/+2, Cr +2/+3/+6, Mn +2…+7. The maximum equals the total s + d valence electrons (Mn +7 in MnO₄⁻; Cr +6 in Cr₂O₇²⁻).
- Colored compounds and paramagnetism — from electrons in partially filled d orbitals (d–d transitions absorb visible light; unpaired d electrons make ions paramagnetic). Detailed in Topic 3.
- Catalytic activity — metal surfaces adsorb reactants and weaken their bonds: Fe in the Haber process, Pt in converters, Ni in fat hydrogenation.
Compounds: oxides run from basic to acidic as Oxidation state Bookkeeping charge of an atom, assuming electrons go to the more electronegative element Full entry → rises — FeO (basic), Cr₂O₃ (amphoteric: dissolves in acid and base), CrO₃ and Mn₂O₇ (acidic). Diagnostic ions: Fe²⁺ (pale green) vs Fe³⁺ (yellow-brown); chromate CrO₄²⁻ (yellow) ⇌ dichromate Cr₂O₇²⁻ (orange), a pH-controlled equilibrium; permanganate MnO₄⁻ (deep purple, powerful oxidant). Iron rusts by an electrochemical process needing water and oxygen; stainless steel resists because its ~11% chromium forms a self-healing Cr₂O₃ film.
How It Works / Step-by-Step Process
From ore to metal:
- Concentrate (crush, grind, froth flotation, magnetic separation).
- Convert to a reducible form: roast sulfides to oxides; make TiCl₄ from TiO₂; dissolve Au with cyanide.
- Reduce: carbon/CO (Fe, Zn); more-reactive metal (Ti by Mg); electrolysis (Mn, Cu); precipitation (Au by Zn).
- Purify: electrolytic refining (Cu) or zone refining (ultrapure metals).
Finding an oxidation state:
- Assign known values (O –2, H +1, halogens –1, Group 1 metals +1).
- Sum must equal the net charge (0 for a compound, the charge for an ion).
- Solve for the transition metal.
Common Confusions
| Do Not Confuse | With | Difference |
|---|---|---|
| All d-block elements | Transition metals | Zn, Cd, Hg have filled d¹⁰ in common ions — d-block but not usually classed as transition metals |
| Fe²⁺ (ferrous) | Fe³⁺ (ferric) | Different oxidation states, colors (pale green vs yellow-brown), redox behavior |
| Higher state = more stable | Higher state = more oxidizing | First-row high states (MnO₄⁻, Cr₂O₇²⁻) are strong oxidants that want electrons back |
| "All metals are extracted with carbon" | Method depends on reactivity | Native Au needs no reduction; Ti needs Mg (Kroll); reactive metals need electrolysis |
| Rusting is simple oxidation by O₂ | Rusting is electrochemical | Rusting needs water + O₂ together; dry iron corrodes far more slowly |
Eli explains
The same idea, in plain words
Explain it like I’m 10
Transition metals are the "trick players" of the periodic table: they can give away different numbers of electrons depending on the game, so the same metal shows up in many disguises — iron can be a +2 guy or a +3 guy, and manganese can even be a +7 guy. Because they have loose electrons that absorb light, their compounds come in brilliant colors, and unpaired electrons make some of them act like tiny magnets. Most hide inside rocks (ores) and must be dug out, cooked with carbon, or zapped with electricity to become the shiny metals in steel, wires, and jewelry.
Worked example
Example 1: How much iron can a hematite shipment yield?
A rail car carries 1.00 × 103 kg of hematite ore that is 72.0% Fe₂O₃ by mass. What mass of iron could be extracted at 100% efficiency?
Step 1 — mass of Fe₂O₃ (percent formula first):
mFe2O3 = 0.720 × 1.00 × 103 kg = 720 kg = 7.20 × 105 g
Step 2 — moles of Fe₂O₃ (M = 2(55.85) + 3(16.00) = 159.69 g/mol):
nFe2O3 = 7.20 × 105 g × 1 mol159.69 g = 4.51 × 103 mol
Step 3 — moles of Fe (two Fe per Fe₂O₃):
nFe = 4.51 × 103 mol × 2 mol Fe1 mol Fe2O3 = 9.02 × 103 mol
Step 4 — mass of Fe:
mFe = 9.02 × 103 mol × 55.85 gmol = 5.04 × 105 g = 504 kg
Answer: About 504 kg of iron — roughly half the ore's mass, since oxygen makes up ~30% of Fe₂O₃ and the gangue the rest.
Example 2: Aluminum needed for a thermite weld
Railroad tracks are welded with the thermite reaction, Fe2O3 + 2Al → 2Fe + Al2O3, which is exothermic enough to produce molten iron. How many grams of aluminum react completely with 500.0 g of Fe₂O₃?
Step 1 — moles of Fe₂O₃:
nFe2O3 = 500.0 g × 1 mol159.69 g = 3.131 mol
Step 2 — moles of Al (mole ratio 2 Al : 1 Fe₂O₃):
nAl = 3.131 mol × 2 mol Al1 mol Fe2O3 = 6.262 mol
Step 3 — mass of Al (M = 26.98 g/mol):
mAl = 6.262 mol × 26.98 gmol = 169 g
Answer: 169 g of aluminum. The chain g → mol → mol → g is the dimensional-analysis pattern used in every stoichiometry problem.
Example 3: Oxidation state of chromium in dichromate
Find the oxidation state of Cr in Cr₂O₇²⁻. Let x = oxidation state of Cr; oxygen is –2, ion charge –2:
2x + 7(-2) = -2 ⇒ 2x = 12 ⇒ x = +6
Answer: Cr is +6 — its maximum state, which is why dichromate is such a strong oxidant.
Key takeaways
- Transition metal = d-block element (Groups 3–12) with a partially filled d subshell; Zn²⁺ (d¹⁰) is d-block but usually excluded.
- Variable oxidation states (Fe +2/+3, Cu +1/+2, Mn +2…+7, Cr +2/+3/+6) because s and d electrons have similar energies; maximum state = total s + d valence electrons.
- Occurrence: oxide and sulfide ores (hematite, chalcopyrite, rutile, chromite); Au, Ag, Pt occur native.
- Extraction follows reactivity: roast sulfides → oxides; reduce with C/CO (Fe, Zn); Kroll with Mg (Ti); cyanide leaching (Au); electrolysis (most reactive).
- Properties: high mp/density/hardness; colored compounds; paramagnetism; catalysis.
- Cr₂O₃ is amphoteric; CrO₄²⁻/Cr₂O₇²⁻ equilibrium is pH-dependent; MnO₄⁻ is a strong oxidant.
- Stainless steel resists rusting via a protective chromium oxide layer.
Check yourself
6 review questions from the chapter. Try each one, then open the answer.
What structural feature defines a transition metal, and why is Zn²⁺ usually excluded?
Show answer
A partially filled d subshell in the atom or a common ion. Zn²⁺ has a filled d¹⁰, so it lacks d-orbital phenomena (color, variable states, magnetism).
Why can gold occur native while iron is always found combined?
Show answer
Gold is extremely unreactive — nothing oxidizes it — so it survives as the free metal. Iron reacts with oxygen and water, so it is locked in oxide ores.
Order the extraction routes (pyrometallurgy, hydrometallurgy, electrometallurgy) by increasing metal reactivity.
Show answer
Pyrometallurgy (Fe, Zn, Cu) → hydrometallurgy (Au, low-grade Cu) → electrometallurgy (most reactive: Mn; also Cu purification).
A furnace reduces 1.00 kg of pure Fe₂O₃. What mass of Fe is produced?
Show answer
n = 1000/159.69 = 6.262 mol Fe2O3; nFe = 12.52 mol; mass = 12.52 × 55.85 = 699 g.
Why do transition metals show variable oxidation states while main-group metals rarely do?
Show answer
The ns and (n-1)d electrons have similar energies, so different numbers can be removed; main-group elements have a clear gap between valence and core electrons.
What is the oxidation state of manganese in MnO₄⁻?
Show answer
x + 4(-2) = -1 ⇒ x = +7.
Study tools & related lessonsKey vocabulary · Related
Key vocabulary
- Ore
- Rock rich enough in a metal compound to mine and process economically
- Native metal
- A metal found uncombined in nature (Au, Ag, Pt)
- Roasting
- Heating a sulfide ore in air to convert it to the oxide
- Smelting
- Reducing a metal oxide with carbon or CO at high temperature
- Hydrometallurgy
- Extracting a metal by dissolving it from the ore in aqueous solution
- Electrometallurgy
- Using electrolysis to deposit or refine a metal
- Oxidation state
- Bookkeeping charge of an atom, assuming electrons go to the more electronegative element
- Zone refining
- Passing a narrow molten zone along a rod to sweep impurities to one end
Sources & references
This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.
Educational content only. It is not medical, legal or professional advice. Found an error? Tell us.