With an atomic number of 4, beryllium has four electrons: two electron shells surround the atom's nucleus and two electrons in each shell. Beryllium is a rigid metal with an atomic mass of 9.0122. It is lightweight but strong and hard. It has a grayish-white color, but beryl crystals also form green emeralds and the sky-blue aquamarine gemstones.
Metals such as copper, iron, aluminum and nickel are often alloyed with beryllium to give them extra strength. The metals are then used to make tools and precision instruments.
Nicholas Louis Vauquelin discovered beryllium in 1797. Friedrich Wohler and A.A. Bussy isolated it independently in 1828.