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The alkaline earth metals make up group 2 of the periodic table: beryllium, magnesium, calcium, strontium, barium and radium. They’re less dramatic than their group 1 neighbours, the alkali metals, but two of them — calcium and magnesium — are among the most important elements for life and for building the modern world.
Where the name comes from
“Earths” was the old alchemists’ word for substances that didn’t melt or change in fire — the oxides of these metals, like lime (calcium oxide) and magnesia (magnesium oxide). Those oxides dissolve in water to give alkaline solutions, hence “alkaline earths”. The metals themselves weren’t isolated until the early 1800s, when Humphry Davy used electrolysis to produce magnesium, calcium, strontium and barium in 1808.
Two outer electrons
Every alkaline earth metal has two electrons in its outer s orbital (Be: [He] 2s², Mg: [Ne] 3s², Ca: [Ar] 4s² …). They lose both to form +2 ions: Mg²⁺, Ca²⁺, Ba²⁺. Removing two electrons takes more energy than removing one, which is why group 2 metals are less reactive than group 1.
Trends down the group (from our element data)
| Element | Melting point (°C) | Density (g/cm³) | First ionization energy (eV) | Electronegativity |
|---|---|---|---|---|
| Beryllium | 1,287 | 1.85 | 9.32 | 1.57 |
| Magnesium | 650 | 1.74 | 7.65 | 1.31 |
| Calcium | 842 | 1.54 | 6.11 | 1.00 |
| Strontium | 777 | 2.64 | 5.69 | 0.95 |
| Barium | 727 | 3.62 | 5.21 | 0.89 |
| Radium | 700 | 5 | 5.28 | 0.9 |
Down the group, atoms get larger, ionization energy falls and reactivity rises. Compared with group 1, these metals are harder, denser and have much higher melting points, because two electrons per atom take part in metallic bonding.
Reactions with water
- Beryllium doesn’t react with water, even when hot.
- Magnesium reacts very slowly with cold water, but burns in steam: Mg + H₂O → MgO + H₂.
- Calcium, strontium and barium react steadily with cold water, fizzing and forming hydroxides: Ca + 2H₂O → Ca(OH)₂ + H₂
The reactivity increases down the group, but even barium is far tamer than sodium.
Burning magnesium
Magnesium ribbon burns with a blinding white light — so bright you shouldn’t look directly at it:
2Mg + O₂ → 2MgO
This made magnesium the flash powder of early photography, and it’s still used in flares and fireworks for white sparks.
Flame colours
| Element | Flame colour |
|---|---|
| Calcium | Orange-red (brick red) |
| Strontium | Crimson red |
| Barium | Apple green |
| Magnesium, beryllium | No distinctive colour |
Strontium salts give fireworks their red, and barium salts their green.
Why calcium and magnesium matter
Calcium
- Bones and teeth are mostly calcium phosphate (hydroxyapatite). It’s the most abundant metal in the human body.
- Limestone, marble and chalk are calcium carbonate. Heating limestone gives lime (CaO), used for cement, steelmaking and farming.
- Gypsum (calcium sulfate) makes plaster and plasterboard.
- Dissolved calcium makes water “hard” and leaves limescale in kettles.
Magnesium
- Every chlorophyll molecule has a magnesium ion at its centre, so photosynthesis depends on it.
- It’s needed by hundreds of enzymes in your body.
- Magnesium alloys are light and strong, used in car parts, laptop cases and aircraft.
- Epsom salt is magnesium sulfate; milk of magnesia is magnesium hydroxide, an antacid.
The others
- Beryllium is light, stiff and transparent to X-rays — used in X-ray windows, aerospace parts and the mirrors of the James Webb Space Telescope. Its dust is toxic, so it’s handled carefully.
- Strontium: red fireworks and flares. Radioactive strontium-90, a fission product, is a concern in nuclear fallout because the body treats it like calcium and deposits it in bone.
- Barium: barium sulfate “meals” make the gut visible on X-rays; it’s so insoluble it passes through safely, even though soluble barium compounds are poisonous. See solubility rules.
- Radium: discovered by Marie and Pierre Curie in 1898, once used in glowing watch dials with tragic consequences for the workers who painted them. It’s intensely radioactive and now has very limited use. See Marie Curie’s elements.
Quick answers
Why is it called group 2? Because they’re in the second column and have two outer electrons.
Which alkaline earth metal is most reactive? Radium (and barium, among the non-radioactive ones).
Are alkaline earth metals found pure in nature? No — they’re too reactive. They occur in minerals like limestone, dolomite and gypsum.
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