Jun 18 2012
Chemical Formula
Na
Topics Covered
BackgroundBasic
InformationKey PropertiesOccurrenceIsotopesProduction
of SodiumHealth AspectsApplications
Background
Sodium carbonate or soda (Na2CO3) was the most popular
sodium compound in ancient times. Soda was called as natron by the Egyptians and
later, the Romans used a similar name for it, natrium which explains the origins
of its chemical symbol Na.
Sodium had its origins from an Arabic word Suda, which means headache as soda
was used sometimes to cure headaches. In Latin, the word suda became sodanum and
hence the name sodium evolved.
In the early 1800s, Davy discovered a way of extracting active elements from
their compounds. In 1807, he prepared sodium by the electrolysis of caustic soda
(NaOH).
Basic Information
The basic information about sodium is listed in the table 1.
Table 1. Basic Properties of sodium
| Name |
Sodium |
| Symbol |
Na |
| Atomic Number |
11 |
| Atomic Weight |
22.98976928 amu |
| Standard State |
Solid at 298 K |
| CAS Registry ID |
7440-23-5 |
| Group in periodic table |
1 |
| Group Name |
Alkali metal |
| Period in periodic table |
3 |
| Block in periodic table |
s-block |
| Color |
Silvery-white |
| Classification |
Metallic |
| Melting Point |
370.95 K (97.80°C or 208.04°F) |
| Boiling Point |
1156 K (883°C or 1621°F) |
| Density |
0.7 g/cm3 |
| Number of Stable Isotopes |
1 |
| Ionization Energy |
5.139 eV |
| Oxidation State |
+1 |
|
|
Key Properties
The key properties of sodium are:
- It is highly reactive, reacting explosively with water
- It is a silver-white metal having a waxy appearance
- It is soft with a bright shiny surface, however as sodium reacts with oxygen
in the air it becomes dull due to the formation of a sodium oxide
(Na2O) film
- The density of sodium is slightly less than water
- It is a good conductor of electricity
- It reacts with oxygen at room temperature
- On heating, it combusts very rapidly, burning with a brilliant golden-yellow
flame
- It reacts with acids to produce hydrogen gas
- It dissolves in mercury forming a sodium amalgam
Occurrence
Sodium cannot be found as a free element in nature. It is highly active
especially with water and oxygen, hence always occurs as part of a compound. The
most common sodium source in the Earth is halite.
Halite is almost pure sodium chloride (NaCl) and is also known as rock
salt. Halite can be found in underground deposits, which formed when ancient oceans
evaporated leaving sodium chloride as well as dry lake beds with large deposits
located the USA, United Kingdom, France, Germany, China and India.
Isotopes
Sodium-23 is the only naturally occurring isotope of sodium.
Although six radioactive isotopes of sodium exist, only two have any
commercial significance. These are described below:
- Sodium 22 and sodium 24 are two radioactive isotopes of sodium, which are
used in medical applications. Sodium 24 is used as an electrolyte tracer to
follow the path sodium takes in a person’s body to see if their uptake levels
are within normal ranges, while sodium 22 is used in nuclear medicine imaging
for positron emission tomography.
- Sodium -24 can also be used in non-medical applications. For instance, it is
used for leak testing in industrial pipelines. Due to the limited penetrating
power of the sodium radiation, detectors are only able to detect the radioactive
sodium at leak points. Sodium 24 is also suited to this application due to its
short half-life of just 15 hours.
Production of Sodium
Sodium metal is produced by the electrolysis of a mixture of sodium chloride
and calcium chloride (CaCl2) using the Down’s Process. The calcium
carbonate is added to bring down the melting point of the mixture to about
600°C.
When an electric current is passed through the molten mixture, the NaCl
decomposes with sodium being attracted to the cathode. It rises to the surface
due to its low density and can be tapped off. Although calcium is also produced, it does not mix with the sodium due its
much higher density of 2.54g/cc.
Health Aspects
Sodium has several important functions is humans, animals and plants. In
humans, sodium controls the amount of fluid present in the cells. A lack or an
excess of sodium can result in cells gaining or losing water. The occurrence of
any of these changes can prevent the cells from performing their normal
functions.
A number of sodium compounds are hazardous as carcinogens and as toxins in
animals and plants. At the same time it is impossible to live without many of
the compounds made of sodium.
Applications
The applications of sodium include:
- It is occasionally used as a heat exchange medium in nuclear power plants.
Liquid sodium is sealed into pipes surrounding the reactor core. Generated heat
is absorbed by sodium and forced through the pipes in a heat exchanger which can be used to generate electricity.
- Sodium is used in making metals such as titanium. Sodium is made to react
with titanium tetrachloride (TiCl4) to yield titanium.
- Sodium is used as a catalyst to make artificial rubber.
- An electric current and sodium vapor combine to form a yellowish glow. This
principle is used for the making of sodium vapor lamps.
- High pressure sodium vapor lamps use mercury that offers a natural color
rendition of light
- Low pressure sodium vapor lamps use a small amount of sodium along with
neon, making the light both bright and economical
Source: AZoM.com