It is interesting that sodium metal is toxic to human tissue, while sodium ions are not only unharmful to humans but also are essential for the normal functioning of the human cells. This difference between sodium metal and sodium ions is due to the extreme reactivity of the metal in comparison with the ion as will be explained later.
Sodium ions are important for the maintenance of the electric potential across the cellular membrane. In particular it is important for the function of muscle cells and nerve fibers. Clinically speaking, sodium channels blockers are used to induce anesthesia during surgery such as dental surgery. Sodium ions along with potassium ions are the main contributors to the electric potential in the cell. Sodium channels agonists are used to induce a state of continuous firing of neurons. Sodium ions contribute less than potassium ions to the resting electric potential of the cell.
Sodium is located in the periodic table below lithium. It has an electronic configuration similar to neon with additional electron in the 3s orbital namely [Ne]3s1. This symbol means that sodium has an additional electron in the electronic energy state number three.
Neon is an inert atom at normal conditions. Its electronic configuration is very stable. Therefore if we remove the one electron of sodium from the 3s orbital we get the electronic configuration of neon which has extra stability energetically. This is actually what is obtained experimentally. Sodium metal can easily lose its outermost electron and the driving force for this is obtaining the stable neon electronic configuration. Sodium has only one naturally occuring isotope.
Sodium reactivity is illustrated by its immediate and exothermic reaction with water to give the oxide of sodium according to the following equation:
2Na + H2O -> Na2O + H2
In addition, its reducing power is used to generate methoxide and ethoxide bases by reaction of sodium with either methanol or ethanol according to the following equation:
Na + CH3OH -> H2 + CH3O-
Sodium metal can dissolve in ammonia to generate solvated electrons which are used in reduction reactions such as the Birch reduction of benzene and the addition of hydrogen to triple bonds to give the trans disubstituted alkene or double bond.
Compounds of sodium are industrially important. Examples of sodium compounds are the eating salt NaCl and sodium carbonate which is industrially important. In addition sodium hydroxide (NaOH ) and sodium sulfate are another two compounds which are industrially important.
Sodium bicarbonate (NaHCO3) is a compound of sodium which is found in the body. It is used by the body as a buffer to neutralize acids and bases that might be ingested as food or drink.
Sodium is important physiologically because it can affect the blood pressure of the human if it is in excess. In addition it can affect the nervous system in two clinically known conditions of sodium balance in the body. These are hypernatremia and hyponatremia.
Sodium ion has an ionic diameter of 204 pm which is comparable to the ionic diameter of Ca++ which has an ionic diameter of 200 pm. Therefore the chemistry of sodium ion and calcium ion are similar to each other. This similarity in chemical behavior is general between atoms in a diagonal relation in the periodic table.
Sodium is a soft element with low melting temperature. It crystallizes in a body centered cubic lattice as all other alkali metals. The melting point of sodium is 97.8 degree celcius and its boiling point is 883 degree celcius. Its density is 0.968 g/cm3.
Sodium has a characteristic color if put in a flame. This fact is used in atomic absorption spectroscopy as a mean to decide if an element is sodium or not.
Sodium like all alkali metals make ionic bonds with non metals such as halogens and chalcogens. This is so due to is electropositive nature which tend to release its electron in the outermost orbital easily. It reacts vigorously with halogens as well as with protic compounds that have protons in their compounds.