72HfHafnium178.49

A real sample of the element Hafnium — Real sample photo

Hafnium (Hf)

“The element named after Copenhagen — predicted by Bohr’s theory, and now the invisible insulation inside every smartphone processor.”

View group 4 →View period 6 →See in trends →

Atomic number72

Atomic mass178.49

Group4

Period6

BlockD-block

PhaseSolid

Electron structure

How its electrons are arranged

[Xe] 4f¹⁴ 5d² 6s²

Shell 1

2e⁻

Shell 2

8e⁻

Shell 3

18e⁻

Shell 4

32e⁻

Shell 5

10e⁻

Shell 6

2e⁻

Computed from the aufbau principle, with known real-world exceptions applied automatically.

🎯 Exam focus

Questions to practise

Try each question yourself first — then open it to read the full model answer.

1How did Bohr’s atomic theory point Coster and Hevesy to the right place to hunt for element 72 in 1923, and which technique confirmed the discovery?

Model answerBohr’s new atomic theory indicated in 1922 that the still-missing element 72 should be a transition metal resembling zirconium, not a rare earth. Acting on that tip-off, Dirk Coster and George de Hevesy searched zirconium minerals in Bohr’s Copenhagen institute, and in early 1923 read the tell-tale lines of element 72 in Norwegian zircon — a discovery confirmed by X-ray spectroscopy.

2Why do nuclear engineers load hafnium into control rods while cladding the fuel in zirconium — two metals that are otherwise chemical twins?

Model answerThe two jobs demand opposite behaviour towards neutrons. Hafnium absorbs neutrons roughly 600 times more eagerly than zirconium, so hafnium rods placed among the fuel soak up neutrons on demand, throttling or shutting down the chain reaction, while zirconium cladding lets neutrons pass freely so the reaction keeps running. It is one of chemistry’s ironies that two metals almost impossible to separate chemically own such opposite nuclear personalities.

3In which common mineral does hafnium always ride along, and why are the two accompanying metals so difficult to part company?

Model answerHafnium always rides along in zircon, the common beach-sand mineral — the sort traced along Bangladesh’s Cox’s Bazar coast — which carries a few percent of hafnium piggybacking on its zirconium. Lanthanide contraction has shrunk the Hf⁴⁺ ion to practically the same radius as Zr⁴⁺, so the pair forms identical compounds and sits side by side in every ore; parting them demands laborious, repeated chemical treatment.

4Which electrical property earned hafnium oxide its job inside every modern microchip transistor, and roughly how many times better is it than silicon dioxide?

Model answerThe property is a high dielectric constant — “high-k”. As the transistor’s gate insulator, hafnium oxide ( $\mathrm{HfO_{2}}$ ) holds far more charge at a given thickness than silicon dioxide could, letting chips shrink further without leaking current; from 2007–08 it replaced $\mathrm{SiO_{2}}$ inside processors. Its k value, roughly 20–25 against silicon dioxide’s 3.9, makes it about five times better.

5Write hafnium’s electron configuration and state its period, group, block and number of valence electrons.

Model answerHafnium’s configuration is [Xe] 4f¹⁴ 5d² 6s². The differentiating electron enters 5d, making it a d-block element; the highest occupied shell is n = 6, so period 6; and with 5d² + 6s² it has four valence electrons, placing it in Group 4 — the same group as titanium and zirconium, its chemical twin.

6What does the name “hafnium” literally mean, and why was that particular name chosen for element 72?

Model answerThe name descends from Hafnia, the Latin name of Copenhagen — so hafnium literally means “Copenhagen”. Coster and Hevesy chose it because the discovery was born in that city, inside Niels Bohr’s Copenhagen institute; naming the new metal after its birthplace honoured both the city and the theory-guided hunt Bohr had set in motion.

Quick answers

One fact, one page

Every key fact of this element has its own clean page — a direct two-line answer first, then the working. Fast to load, easy to share.

Electron configurationThe full arrangement, step by step ValencyHow many bonds it forms Atomic massThe standard weight, explained Metal or nonmetalWhich family it belongs to Everyday usesWhere you meet it daily

Your progress

You have explored 0 of 118 elements

Study

The notes

About the element

Characteristics

Electron configuration [Xe] 4f¹⁴ 5d² 6s² — period 6, group 4, d-block, four valence electrons; the workhorse ion is Hf⁴⁺.
A near-perfect chemical twin of zirconium: lanthanide contraction has shrunk Hf⁴⁺ to practically the same ionic radius as Zr⁴⁺, so the two metals occur together everywhere and are notoriously hard to separate.
Nuclear split personality: hafnium devours neutrons roughly 600 times more eagerly than zirconium — which is exactly why one twin becomes reactor control rods while the other sheaths the fuel.
A refractory, corrosion-proof metal (melting point 2233 °C); its carbide HfC, melting near 3900 °C, stands among the most heat-proof compounds known.

Appearance

A silvery-grey, lustrous transition metal that resists corrosion and keeps its polish in air. It is noticeably heavy for its size (density about 13.3 g/cm³) and rolls into tough, corrosion-proof foils and wires.

Real world

Where you meet it

✦ Uses

Control rods in nuclear reactors and naval propulsion plants — hafnium’s neutron-hungry isotopes throttle or shut down the chain reaction on demand.
High-k gate insulation in modern microchips: since 2007–08, hafnium oxide ( $\mathrm{HfO_{2}}$ ) has replaced silicon dioxide inside processors, including the chip in your smartphone.
Nickel superalloy turbine blades — a few percent of hafnium toughens the grain boundaries of blades in jet engines and power turbines.
Ultra-hot engineering: hafnium carbide, alone or alloyed with tantalum carbide, armours rocket throats and cutting tools, while old-style camera flashbulbs once burned hafnium foil.

◍ Everyday examples

The processor inside a smartphone or laptop almost certainly depends on a hafnium-oxide insulating layer only a few atoms thick.
Zircon — the beach-sand mineral being traced along Bangladesh’s Cox’s Bazar coast — always carries a few percent of hafnium piggybacking on the zirconium.
Nuclear submarines and aircraft-carrier fleets glide for decades on reactors steered by hafnium control rods.

Story

History & name

Niels Bohr’s new atomic theory signalled in 1922 that the still-missing element 72 should be a transition metal resembling zirconium rather than a rare earth. Acting on that tip-off, Dirk Coster and George de Hevesy, working in Bohr’s Copenhagen institute, shot X-rays through Norwegian zircon and in early 1923 read the tell-tale lines of the new element — a discovery guided by theory and confirmed by X-ray spectroscopy. They named it hafnium after Hafnia, the Latin name of Copenhagen, honouring the city of its birth.

Name originLatin Hafnia — “Copenhagen”, the city where Coster and Hevesy discovered it in 1923.

Neighbours

Nearby elements

The elements that sit right beside this one on the table — often the closest chemical cousins.

70YbYtterbium173.05 71LuLutetium174.97 73TaTantalum180.95 74WTungsten183.84