(Rb)
History
Rubidium was discovered (1861) spectroscopically by German scientists Robert Bunsen and Gustav Kirchhoff and named after the two prominent red lines of its spectrum. Rubidium and cesium often occur together in nature. Rubidium, however, is more widely scattered and seldom forms a natural mineral; it is found only as an impurity in other minerals, ranging in content up to 5 percent in such minerals as lepidolite, pollucite, and carnallite.
The primary difficulty associated with the production of pure rubidium is that it is always found together with cesium in nature and is also mixed with other alkali metals. Because these elements are very similar chemically, their separation presented numerous problems before the advent of ion-exchange methods and ion-specific complexing agents such as crown ethers. Once pure salts have been prepared, it is a straightforward task to convert them to the free metal. This can be done by electrolysis of the fused cyanide or by reduction with calcium or sodium followed by fractional distillation.
Properties
Rubidium is an alkali metal in group IA of the periodic table with atomic number 37, an atomic weight of 85.47, and a density of 1.53 Mg/m3. Its melting point is 38.9 °C, and it boils at 688 °C. Its atomic radius is 0.248 nm and the (+1) ionic radius is 0.148 nm.
Number of p+ n° and e-
Rubidium has a number of protons of 37, neutrons 48 and electrons 37.
Uses and compounds
There are relatively few commercial uses for rubidium or its compounds. Rubidium is used to make atomic clocks. But these clocks are used only for very specialized purposes where very precise time-keeping is important. Rubidium is also used to make photocells. A photocell is a device for converting light energy into electrical energy. But other members of the alkali family are still preferred for this application.
Barium
(Ba)
History
Alchemists in the early middle Ages knew about some barium minerals. Smooth pebble-like stones of mineral barite found in Bologna, Italy, were known as "Bologna stones." Witches and alchemists were attracted to them because after exposure to light they would glow for years. The phosphorescent properties of barite heated with organics were described by V. Casciorolus in 1602.
Barium metal was isolated for the first time in 1808 by English chemist Sir Humphrey Davy in London. Davy followed the advice of Swedish chemist Jons Jacob Berzelius, who had told him that barium sulfate could be decomposed by electrolysis. This was correct, and Davy isolated strontium in a similar way. The experimental details are on our strontium page.
The element was called barium because it was found in barite (barium sulfate) a mineral given its name because of its high density. The Greek ‘barys’ means heavy.
Properties
Barium has a melting point of 725°C, boiling point of 1640°C, specific gravity of 3.5 (20°C), with a valence of 2.its atomic radius is 2.78 .Barium is a soft metallic element. In its pure form, it is silvery white. The metal oxidizes readily and should be stored under petroleum or other oxygen-free liquids. Barium decomposes in water or alcohol. Impure barium sulfide phosphoresces following exposure to light. All barium compounds that are soluble in water or acid are poisonous.
Number of p+, n° and e-
The purest type of atom is called an element. Atoms are composed of three kinds of smaller particles, called protons, neutrons and electrons. Protons and neutrons are made up of even smaller particles called quarks. The number of protons, the number of neutrons and the number of electrons an atom has determines what the element it is. Barium has a number of protons is 56, neutrons 81 and electrons is 56.