Sodium (symbol Na, from the Latin name natrium) is the chemical element number 11 in the periodic table of elements. It follows that its nucleus includes 11 protons, and 11 electrons orbit around it (according to the simplified model known as "Niels Bohr atom"). Even if many isotopes can be artificially made, all decay in a short time. As a result, all sodium found in nature (mainly in sea water) has the composition 11Na23, meaning that the nucleus includes 12 neutrons. The atomic mass of sodium is 22.9898; if it is rounded, it would be 23.

Properties 

Sodium is a light, silver-coloured metal. Sodium is so soft that it can be easily cut with a knife. When it is cut, the surface will become white over time. This is because it reacts with air to form sodium hydroxide and sodium carbonate. Sodium is a little lighter than water; when it reacts with water it floats and reacts. This reaction is very fast. Hydrogen and sodium hydroxide are produced and lots of heat is created which usually causes the hydrogen to ignite. Since sodium melts at a low temperature, it melts when it reacts with water. It has one valence electron which is removed easily, making it highly reactive. 

Compared with other alkali metals (metals in the first column of the periodic table), sodium is usually less reactive than potassium and more reactive than lithium.

Chemical compounds 
These are chemical compounds that contain sodium ions. Sodium only exists in 1 oxidation state: +1.

Sodium aluminum fluoride, used to make aluminum
Sodium amide, very strong base
Sodium arsenite, colorless solid, very toxic
Sodium arsenate, oxidizing agent, very toxic
Sodium azide, used in airbags
Sodium bicarbonate, baking soda, used in cooking
Sodium bismuthate, oxidizing agent, used to test for manganese
Sodium bisulfate, acidic, used to increase pH
Sodium bromate, oxidizing agent, used to dye hair
Sodium bromide, rare, used in some medicine
Sodium carbonate, used to make glass
Sodium chlorate, used in some explosives
Sodium chlorite, used in disinfectants
Sodium chloride, table salt
Sodium chromate, yellow, oxidizing agent, toxic
Sodium dichromate, orange, oxidizing agent, toxic
Sodium fluoride, used in toothpastes, bitter, toxic in large doses
Sodium hydroxide, lye, used in soap, strong base
Sodium hypochlorite, bleach, disinfectant
Sodium hypophosphite, reducing agent, poisonous
Sodium iodate, oxidizing agent, prevents iodine deficiency
Sodium iodide, weak reducing agent, prevents iodine deficiency
Sodium manganate, rare green solid
Sodium nitrate, used in blasting powder
Sodium nitrite, used in food preservation
Sodium periodate, oxidizing agent
Sodium permanganate, less common than potassium permanganate, oxidizing agent
Sodium phosphate, various uses
Sodium phosphide, catalyst
Sodium phosphite, toxic, reducing agent
Sodium selenate, strong oxidizing agent, other selenium compounds
Sodium selenide, strong reducing agent, reactive
Sodium selenite, weak oxidizing agent, vitamin supplement
Sodium sulfate, bitter, laxative
Sodium sulfite, weak reducing agent, used to preserve dried food
Sodium tellurate, strong oxidizing agent
Sodium telluride, strong reducing agent, reacts with air easily
Sodium tellurite, main tellurite compound

Discovery and name 

Sodium was discovered by Sir Humphrey Davy, an English scientist, back in 1807. He made it by the electrolysis of sodium hydroxide. It is named after soda, a name for sodium hydroxide or sodium carbonate.

Use as element 
It is used in the preparation of organic compounds. It is also used in the street lights that are orange, and ultra violet lights.

Use as compounds 

Sodium compounds are used in soaps, toothpaste, baking and antiacids.
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Occurrence and production 
Sodium does not exist as an element in nature; its easily removed valence electron is too reactive. It exists as an ion in chemical compounds. Sodium ions are found in the ocean. It is also found as sodium chloride in the earth's crust, where it is mined.

Sodium is normally made by electrolysis of very hot sodium chloride that was melted.

Use in organisms 
Sodium ion in the form of sodium chloride is needed in the human body, but large amounts of it cause problems, which is why one should not eat too much salt and other food items with huge sodium amount (such as biscuits with baking soda). Many organisms in the ocean depend on the proper concentration of ions in sea water to live.

Related pages
 List of common elements
 Hyponatremia (a medical problem caused by not having enough sodium in the body).

References 

Alkali metals
Chemical elements