The alkaline earth metals are named after their oxides, the alkaline earths, whose old-fashioned names were beryllia, magnesia, lime, strontia and baryta. These were named alkaline earths because of their intermediate nature between the alkalis (oxides of the alkali metals) and the rare earths (oxides of rare earth metals). The classification of some apparently inert substances as 'earths' is millennia old. The earliest known system used by the ancient Greeks consisted of four elements, including earth. This system was later refined by philosophers and alchemists such as Aristotle (4th century BC), Paracelsus (first half of 16th century), John Becher (mid 17th century) and Georg Stahl (late 17th century), with later thinkers subdividing 'earth' into three or more types. The realisation that 'earths' were not elements but compounds is attributed to the chemist Antoine Lavoisier. In his Trait mentaire de Chimie (Elements of Chemistry) of 1789 he called them Substances simples salifiables terreuses, or 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.
The alkaline earth metals are silvery colored, soft, low density 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. These elements all have two electrons in their outermost shell, so the energetically preferred state of achieving a filled electron shell is to lose two electrons to form doubly chargedpositiveion.
Metal phosphide used as a raw material in the synthesis of alkalineearthmetal halophosphate phosphor activated by antimony and manganese acts as a reducing agent to prevent oxidation of the antimony and manganese.
Synthesis of alkalineearthmetal halophosphate phosphor activated by antimony and manganese requires that the activators be provided in their lowest oxidation states, that is, trivalent (3.sup.+) antimony and divalent (2.sup.+) manganese.
We have found that during the synthesis of alkalineearth halophosphate phosphor activated by antimony and manganese, the addition of a metal phosphide as a raw material will ensure that the antimony and manganese activators are available in their lowest oxidation states (that is, trivalent antimony and divalent manganese).
The alkalineearthmetals, like the alkalimetals, are too reactive to be found in nature except as their compounds; the two valence electrons completing an s-subshell are readily lost, and ions with +2 charges are formed.
The alkalineearthmetals are silvery colored, soft, low-density metals, which react readily with halogens to form ionic salts, and with water, though not as rapidly as the alkalimetals, to form strongly alkaline (basic) hydroxides.
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