Chromium
Chromium is a hard, lustrous metal best known for the mirror-bright shine it gives to plated surfaces and the corrosion resistance it lends to stainless steel. Its name comes straight from its chemistry: chromium compounds span a remarkable range of vivid colors, from deep greens to fiery oranges and reds.
- Group · Period
- 6 · 4
- At room temp
- solid
- Melts at
- 2180 K
- Density
- 7.15 g/cm³
- Discovered
- 1797
Uses
Chromium’s biggest industrial role is in stainless steel, where it’s added in significant amounts to give the alloy its signature resistance to rust and staining. It’s also widely used in decorative and protective chrome plating, giving car parts, fixtures, and tools a bright, durable, mirror-like finish that resists corrosion and wear. Chromium compounds serve as pigments in paints and dyes, prized for their vivid and stable colors.
Beyond these everyday applications, chromium alloys are used in high-temperature and high-stress environments, such as certain furnace parts and cutting tools, where its hardness and resistance to oxidation are particularly valuable.
History
French chemist Louis Nicolas Vauquelin isolated chromium in 1797 from a bright orange mineral called crocoite, after noticing that the mineral contained a previously unknown metal. He went on to show that this new element was responsible for the color in several gemstones and minerals. Vauquelin named it chromium, from the Greek word “chroma” for color, a fitting choice given how strikingly its compounds range across the color spectrum.
Fun facts
- Chromium is what makes stainless steel 'stainless' — added in sufficient amounts, it forms a thin, self-repairing oxide layer that resists rust and staining.
- Its name comes from the Greek word 'chroma,' meaning color, because its compounds range so widely across the color spectrum.
- Trace amounts of chromium are responsible for the red color of rubies and the green color of emeralds.
Frequently asked questions
What actually makes stainless steel resistant to rust?
Stainless steel contains a significant amount of chromium, which reacts with oxygen in the air to form an extremely thin, invisible layer of chromium oxide on the surface. Unlike ordinary rust, this layer is stable and tightly bonded to the metal, and if it's scratched, it quickly reforms — effectively sealing the steel off from further corrosion.
Is chrome plating the same as chromium metal?
Chrome plating is a thin layer of chromium metal deposited onto another material, usually steel, through an electroplating process. It's genuinely chromium, just applied as a coating rather than used as a solid piece — the thin layer is enough to give the shiny, corrosion-resistant finish without needing the whole object to be made of chromium.
Why do chromium compounds come in so many different colors?
Chromium can exist in several different oxidation states, and each one interacts with light differently, producing a distinct color. That variety is exactly what led to its name, and it's also why trace amounts of chromium are responsible for the color in gemstones like rubies and emeralds, depending on the surrounding crystal structure.
Compounds
4 notable compounds containing Cr
- CrCl3salt
Chromium(III) chloride
A solid that appears violet when anhydrous but shifts toward green as it picks up water, a striking demonstration of how coordinated water molecules change a transition metal ion's color.
Used for: Precursor for chromium catalysts and mordant in textile dyeing
- Cr2O3oxide
Chromium(III) oxide
A stable, hard green solid representing chromium's common +3 oxidation state. Its intense color and chemical inertness have made it one of the longest-used green pigments in industry.
Used for: Green pigment for paints, ceramics, and glass; abrasive polishing compound
- CrO3oxide
Chromium(VI) oxide
A dark red, highly reactive solid featuring chromium in its +6 state. It dissolves in water to form chromic acid, a powerful oxidizer that is far more aggressive than chromium's more common +3 compounds.
Used for: Industrial chromium electroplating and metal-finishing baths
- K2Cr2O7salt
Potassium dichromate
A bright orange crystalline salt and one of the most recognizable chromium(VI) compounds, prized in classical chemistry for its strong, reliable oxidizing power in acidic solution.
Used for: Oxidizing agent in redox titrations and historically in leather tanning
Isotopes
29 known isotopes
Swipe to see all columns →
| Isotope | Natural abundance | Half-life | Decay mode | Mass excess | Binding energy / nucleon | Decay width |
|---|---|---|---|---|---|---|
| Cr-50 | 4.345% | 1.3E+18 Y | Double electron capture | -50,261.36 keV | 8,701.02 keV | 1.11 × 10-41 eV |
| Cr-52 stable | 83.789% | Stable | — | -55,419.51 keV | 8,775.99 keV | — |
| Cr-53 stable | 9.501% | Stable | — | -55,287.62 keV | 8,760.21 keV | — |
| Cr-54 stable | 2.365% | Stable | — | -56,935.38 keV | 8,777.97 keV | — |
Show all 29 isotopes
| Cr-42 | — | 13.3 ms | Electron capture / beta-plus decay (100%), ECP (94.4%) | 7,060 keV | 7,456 keV | 3.43 × 10-14 eV |
| Cr-43 | — | 21.2 ms | Electron capture / beta-plus decay (100%), ECP (79.3%), EC2P (11.6%) | -1,970 keV | 7,680 keV | 2.15 × 10-14 eV |
| Cr-44 | — | 42.8 ms | Electron capture / beta-plus decay (100%), ECP (7%) | -13,421.9 keV | 7,949.63 keV | 1.07 × 10-14 eV |
| Cr-45 | — | 60.9 ms | Beta-plus decay (100%), Beta-plus, proton emission (34.4%) | -19,514.8 keV | 8,087.73 keV | 7.49 × 10-15 eV |
| Cr-46 | — | 0.26 s | Electron capture / beta-plus decay (100%) | -29,471.57 keV | 8,303.82 keV | 1.75 × 10-15 eV |
| Cr-47 | — | 500 ms | Electron capture / beta-plus decay (100%) | -34,563.09 keV | 8,407.21 keV | 9.12 × 10-16 eV |
| Cr-48 | — | 21.56 h | Electron capture / beta-plus decay (100%) | -42,821.31 keV | 8,572.26 keV | 5.88 × 10-21 eV |
| Cr-49 | — | 42.3 m | Electron capture / beta-plus decay (100%) | -45,332.35 keV | 8,613.28 keV | 1.80 × 10-19 eV |
| Cr-51 | — | 27.704 d | Electron capture (100%) | -51,450.72 keV | 8,711.99 keV | 1.91 × 10-22 eV |
| Cr-55 | — | 3.497 m | Beta-minus decay (100%) | -55,110.32 keV | 8,731.94 keV | 2.17 × 10-18 eV |
| Cr-56 | — | 5.94 m | Beta-minus decay (100%) | -55,285.13 keV | 8,723.26 keV | 1.28 × 10-18 eV |
| Cr-57 | — | 21.1 s | Beta-minus decay (100%) | -52,524.99 keV | 8,663.4 keV | 2.16 × 10-17 eV |
| Cr-58 | — | 7.0 s | Beta-minus decay (100%) | -51,991.81 keV | 8,644 keV | 6.52 × 10-17 eV |
| Cr-59 | — | 0.74 s | Beta-minus decay (100%) | -48,115.93 keV | 8,568.6 keV | 6.17 × 10-16 eV |
| Cr-60 | — | 0.49 s | Beta-minus decay (100%), Beta-minus, neutron emission | -46,908.5 keV | 8,540.19 keV | 9.31 × 10-16 eV |
| Cr-61 | — | 234 ms | Beta-minus decay (100%), Beta-minus, neutron emission | -42,496.5 keV | 8,460.17 keV | 1.95 × 10-15 eV |
| Cr-62 | — | 206 ms | Beta-minus decay (100%), Beta-minus, neutron emission | -40,852.61 keV | 8,427.39 keV | 2.21 × 10-15 eV |
| Cr-63 | — | 129 ms | Beta-minus decay (100%), Beta-minus, neutron emission | -36,178.3 keV | 8,347.54 keV | 3.54 × 10-15 eV |
| Cr-64 | — | 42.9 ms | Beta-minus decay (100%), Beta-minus, neutron emission | -33,639.98 keV | 8,303.56 keV | 1.06 × 10-14 eV |
| Cr-65 | — | 27 ms | Beta-minus decay (100%) | -28,310 keV | 8,218 keV | 1.69 × 10-14 eV |
| Cr-66 | — | 24 ms | Beta-minus decay (100%) | -25,140 keV | 8,168 keV | 1.90 × 10-14 eV |
| Cr-67 | — | — | Unknown | -19,270 keV | 8,079 keV | — |
| Cr-68 | — | 360 ns | Beta-minus decay (100%), Beta-minus, neutron emission (0%) | -15,690 keV | 8,026 keV | 1.27 × 10-9 eV |
| Cr-69 | — | 620 ns | Beta-minus decay, Beta-minus, neutron emission, B-2N | -9,630 keV | 7,939 keV | 7.36 × 10-10 eV |
| Cr-70 | — | 620 ns | Beta-minus decay, Beta-minus, neutron emission, B-2N | -5,640 keV | 7,884 keV | 7.36 × 10-10 eV |