Group 2 — two outer electrons, and the structural backbone of life
Harder, denser and less violent than their group 1 neighbours, the alkaline earth metals give up two electrons instead of one. That single difference is why calcium builds bone and shell, why magnesium sits at the centre of chlorophyll, and why beryllium is stiff enough for space telescopes.
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Every member
What defines them
A full ns² outer shell is not stable enough to keep, so these metals lose both electrons and form +2 ions. The doubled charge means their compounds are held together far more strongly than the alkali metals' — which is exactly why they make good structural minerals.
Beryllium barely reacts with water at all. Magnesium needs steam. Calcium fizzes steadily, strontium faster, barium fastest. The same downward trend as group 1, but shifted several notches calmer.
Their carbonates and sulfates are largely insoluble, which is why limestone, marble, chalk, gypsum and seashells exist as durable rock rather than dissolving back into the sea.
Periodic trends
Down the group: atoms grow, ionisation energy falls, reactivity rises, and hydroxide solubility increases while sulfate solubility decreases. Compared with group 1 at the same period, group 2 atoms are smaller, denser, harder and higher-melting.
In the world
Aerospace alloys and X-ray windows — it is nearly transparent to X-rays and six times stiffer than steel per unit weight. The James Webb Space Telescope's mirrors are beryllium.
Lightweight alloys for cars, laptops and bicycle frames; the metal at the heart of every chlorophyll molecule; and the brilliant white flare of old flash photography.
Cement, plaster, steelmaking, and every bone and shell on the planet. Calcium carbonate is the most-quarried mineral on Earth.
The crimson in fireworks and emergency flares. Strontium-90 from weapons fallout is dangerous precisely because the body treats it as calcium.
Barium sulfate is so insoluble that a "barium meal" lets radiologists image the digestive tract without poisoning the patient.
Historically luminous paint and early cancer therapy. Both uses killed people; neither is used today.
Handling
Beryllium dust causes chronic berylliosis, an incurable lung disease, at very low exposures — it is by far the most dangerous member. Soluble barium salts are acutely toxic. Radium is intensely radioactive. Magnesium and calcium are essential nutrients in ionic form, but magnesium metal burns at 3,100 °C and cannot be extinguished with water or CO₂.
Worth knowing
Common questions
Their oxides — lime, magnesia, baryta — were classified by early chemists as "earths" because they resisted melting and were insoluble. Dissolve what little does dissolve, and the result is alkaline. The name survived even after the metals themselves were isolated.
It is unusually small and holds its electrons unusually tightly, so its bonding is largely covalent rather than ionic. That diagonal similarity to aluminium is a general pattern for period-2 elements, which all behave more like the element down-and-right of them than like the rest of their own group.
Because chemistry cannot tell isotopes apart, and strontium sits directly below calcium with the same +2 charge and a similar ionic radius. The body's calcium machinery picks it up and files it in the skeleton, where it then irradiates bone marrow for decades.
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