The symbol is Na.
Sodium's atomic mass is 22.99
Although sodium is the sixth most abundant element on earth and comprises about 2.6% of the earth's crust, it is a very reactive element and is never found free in nature. Pure sodium was first isolated by Sir Humphry Davy in 1807 through the electrolysis of caustic soda (NaOH). Since sodium can ignite on contact with water, it must be stored in a moisture free environment.
It tarnishes easily and has a low melting point and density. Therefore, sodium is usually stored in mineral oil or kerosene. Chemically, sodium is highly reactive with the halogen family to form ionic salts. For example, sodium is commonly found combined with chloride to form NaCl, known to us as table salt. It has one electron in the outermost electron shell and thus wants to give up one electron to a highly electronegative element. Within the alkali metals, sodium is more reactive than lithium, but less reactive than potassium. Its ionization energy is higher than potassium, but lower than lithium. Sodium is also more metallic than lithium. When exposed to air, sodium oxidizes immediately. When burned, sodium forms sodium peroxide (Na2O2) or oxide (NaO2). If burned in oxygen under pressure, sodium superoxide (NaO2) is formed.