Everything about Alkaline Earth totally explained
The
alkaline earth metals are a
series of
elements comprising
Group 2 (
IUPAC style) of the
periodic table:
beryllium (
Be),
magnesium (
Mg),
calcium (
Ca),
strontium (
Sr),
barium (
Ba) and
radium (
Ra). The alkaline earth metals provide a good example of group trends in properties in the periodic table, with well characterized homologous behavior down the group.”
The alkaline earth metals are silvered colored, soft
metals, which react readily with
halogens to form
ionic salts, and with
water, though not as rapidly as the
alkali metals, to form strongly
alkaline (
basic)
hydroxides. For example, where
sodium and
potassium react with water at room temperature,
magnesium reacts only with
steam and
calcium with hot water:
» Mg + 2 H
2O → Mg(OH)
2 + H
2
Beryllium is an exception: It doesn't react with water or steam, and its halides are covalent.
All the alkaline earth metals have two
electrons in their valence shell, so the energetically preferred state of achieving a filled
electron shell is to lose two electrons to form doubly
charged positive ions.
The alkaline earth metals are named after their
oxides, the
alkaline earths, whose old-fashioned names were
beryllia,
magnesia,
lime,
strontia and
baryta. These oxides are basic (alkaline) when combined with water. "Earth" is an old term applied by early chemists to nonmetallic substances that are insoluble in water and resistant to heating--properties shared by these oxides. The realization that these earths were not elements but
compounds is attributed to the chemist
Antoine Lavoisier. In his
Traité Élémentaire de Chimie (
Elements of Chemistry) of
1789 he called them salt-forming earth elements. Later, he suggested that the alkaline earths might be metal oxides, but admitted that this was mere conjecture. In
1808, acting on Lavoisier's idea,
Humphry Davy became the first to obtain samples of the metals by
electrolysis of their molten earths.
Biological occurrences
- Beryllium's low aqueous solubility means it's rarely available to biological systems; it has no known role in living organisms, and when encountered by them, is generally highly toxic.
Magnesium and calcium are ubiquitous and essential to all known living organisms. They are involved in more than one role, with for example Mg/Ca ion pumps playing a role in some cellular processes, magnesium functioning as the active center in some enzymes, and calcium salts taking a structural role (for example bones).
Strontium and barium have a lower availability in the biosphere. They generally have no natural role in biological systems, (perhaps the only documented example is the primitive marine organism Acantharea, which uses strontium sulfate to build its exoskeleton). These elements have some uses in medicine, for example "barium meals" in radiographic imaging, whilst strontium compounds are employed in some toothpastes.
Radium has a low availability and is highly radioactive, making it toxic to life.
Further Information
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