Trinket. Calcium.

<div>   </div> <div> <strong> Atomic number     <span class = "Apple-tab-span" style = "white-space: pre;"> </span>20</strong></div> <div> <strong> Atomic mass     <span class = "Apple-tab-span" style = "white-space: pre;"> </span>40,078</strong></div> <div> <strong> Density, kg / m? < span class = "Apple-tab-span" style = "white-space: pre;"> </span>   1550 </strong> </div> <div> <strong> Temperature </strong></div> <div> <strong> melting, ° С <span class = "Apple-tab-span" style = "white- space: pre; "> </span>       838 </strong> </div> <div>   </div> <div> Calcium is a soft, reactive alkaline earth metal of a silvery-white color. Ca compounds - limestone, marble, gypsum (as well as lime - a product of limestone burning) were already used in the construction business in ancient times. Until the end of the 18th century, chemists considered lime to be a simple body. In 1789 A. Lavoisier suggested that lime, magnesia, barite, alumina and silica are complex substances. In 1808, G. Davy, subjecting a mixture of wet slaked lime with mercury oxide to electrolysis with a mercury cathode, prepared an amalgam Ca, and after removing mercury from it, he obtained a metal called "Calcium" (from Latin calx, genus calcis - lime) . </div> <div>   </div>