Rubidium is a soft, whitish-grey metal in the alkali group. Its atomic number is 37 and it has 2 stable isotopes. The isotope 85Rb accounts for 72% of the total mass. It is a rare element, but it has the highest melting point of any alkali metal, with the exception of potassium.
It is readily soluble in hot water and moderately soluble in cold. It oxidizes sulphur to form stannic salts, and is used for gelatin film in photography and chrome tanning. It is also an important reagent in organic chemistry. It is a strong oxidizing agent and is used to determine chromium concentrations in water samples by measuring the change in absorbance at 600 nm.
Chromium is a lustrous, hard metal that primarily occurs as the oxides Cr2O3 and CrO2. It is commonly used for producing chromic acid and chromium pigments. It is also widely used in alloying and metallurgy.
Hexavalent chromate and dichromate compounds are powerful oxidants, as well as being carcinogenic and toxic. They are most often ingested orally, but may also be inhaled. The primary symptoms of exposure to hexavalent chromium are irritation of the lungs and bronchiotracheal tract. Various hexavalent chromium complexes can also cause occupational diseases, including nephrotoxicity and liver damage.
The hexavalent chromium center has an unpaired electron in its d orbital. This gives it a high affinity for oxygen, and the intense color of hexavalent chromium results from the strong interaction between the d and f orbitals. Chromium(VI) is known to interact with biomolecules and bind to DNA.