Periodic Table > Sodium
 

Glossary


Allotropes
Some elements exist in several different structural forms, called allotropes. Each allotrope has different physical properties.


For more information on the Visual Elements image see the Uses and properties section below.

 

Glossary


Group
A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.


Period
A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.


Block
Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp (s), principal (p), diffuse (d), and fundamental (f).


Atomic number
The number of protons in an atom.


Electron configuration
The arrangements of electrons above the last (closed shell) noble gas.


Melting point
The temperature at which the solid–liquid phase change occurs.


Boiling point
The temperature at which the liquid–gas phase change occurs.


Sublimation
The transition of a substance directly from the solid to the gas phase without passing through a liquid phase.


Density (g cm−3)
Density is the mass of a substance that would fill 1 cm3 at room temperature.


Relative atomic mass
The mass of an atom relative to that of carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists, the value given is the abundance weighted average.


Isotopes
Atoms of the same element with different numbers of neutrons.


CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems.


Fact box

 
Group Melting point 97.794°C, 208.029°F, 370.944 K 
Period Boiling point 882.940°C, 1621.292°F, 1156.090 K 
Block Density (g cm−3) 0.97 
Atomic number 11  Relative atomic mass 22.990  
State at 20°C Solid  Key isotopes 23Na 
Electron configuration [Ne] 3s1  CAS number 7440-23-5 
ChemSpider ID 4514534 ChemSpider is a free chemical structure database
 

Glossary


Image explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.


Appearance

The description of the element in its natural form.


Biological role

The role of the element in humans, animals and plants.


Natural abundance

Where the element is most commonly found in nature, and how it is sourced commercially.

Uses and properties

 
Image explanation
The two lines in a circle represents sodium, and is one of the element symbols developed by John Dalton in the 19th century. The orange glow is like the colour of sodium street lighting and the spiked ‘flash’ symbol reflects the element's high reactivity.
Appearance
Sodium is a soft metal that tarnishes within seconds of being exposed to the air. It also reacts vigorously with water.
Uses
Sodium is used as a heat exchanger in some nuclear reactors, and as a reagent in the chemicals industry. But sodium salts have more uses than the metal itself.

The most common compound of sodium is sodium chloride (common salt). It is added to food and used to de-ice roads in winter. It is also used as a feedstock for the chemical industry.

Sodium carbonate (washing soda) is also a useful sodium salt. It is used as a water softener.
Biological role
Sodium is essential to all living things, and humans have known this since prehistoric times. Our bodies contain about 100 grams, but we are constantly losing sodium in different ways so we need to replace it. We can get all the sodium we need from our food, without adding any extra. The average person eats about 10 grams of salt a day, but all we really need is about 3 grams. Any extra sodium may contribute to high blood pressure. Sodium is important for many different functions of the human body. For example, it helps cells to transmit nerve signals and regulate water levels in tissues and blood.
Natural abundance
Sodium is the sixth most common element on Earth, and makes up 2.6% of the Earth’s crust. The most common compound is sodium chloride. This very soluble salt has been leached into the oceans over the lifetime of the planet, but many salt beds or ‘lakes’ are found where ancient seas have evaporated. It is also found in many minerals including cryolite, zeolite and sodalite.

Because sodium is so reactive it is never found as the metal in nature. Sodium metal is produced by electrolysis of dry molten sodium chloride.
 
Glossary

Atomic radius, non-bonded
Half of the distance between two unbonded atoms of the same element when the electrostatic forces are balanced. These values were determined using several different methods.


Covalent radius
Half of the distance between two atoms within a single covalent bond. Values are given for typical oxidation number and coordination.


Electron affinity
The energy released when an electron is added to the neutral atom and a negative ion is formed.


Electronegativity (Pauling scale)
The tendency of an atom to attract electrons towards itself, expressed on a relative scale.


First ionisation energy
The minimum energy required to remove an electron from a neutral atom in its ground state.

Atomic data

 
Atomic radius, non-bonded (Å) 2.27 Covalent radius (Å) 1.60
Electron affinity (kJ mol−1) 52.867 Electronegativity
(Pauling scale)
0.93
Ionisation energies
(kJ mol−1)
 
1st
495.845
2nd
4562.444
3rd
6910.28
4th
9543.36
5th
13353.6
6th
16612.85
7th
20117.2
8th
25496.25
 

Glossary

Data for this section been provided by the British Geological Survey.


Relative supply risk

An integrated supply risk index from 1 (very low risk) to 10 (very high risk). This is calculated by combining the scores for crustal abundance, reserve distribution, production concentration, substitutability, recycling rate and political stability scores.


Crustal abundance (ppm)

The number of atoms of the element per 1 million atoms of the Earth’s crust.


Recycling rate

The percentage of a commodity which is recycled. A higher recycling rate may reduce risk to supply.


Substitutability

The availability of suitable substitutes for a given commodity.
High = substitution not possible or very difficult.
Medium = substitution is possible but there may be an economic and/or performance impact
Low = substitution is possible with little or no economic and/or performance impact


Production concentration

The percentage of an element produced in the top producing country. The higher the value, the larger risk there is to supply.


Reserve distribution

The percentage of the world reserves located in the country with the largest reserves. The higher the value, the larger risk there is to supply.


Political stability of top producer

A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators.


Political stability of top reserve holder

A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators.


Supply risk

 
Relative supply risk 4
Crustal abundance (ppm) 23600
Recycling rate (%) Unknown
Substitutability Unknown
Production concentration (%) 24.3
Reserve distribution (%) Unknown
Top 3 producers
  • 1) China
  • 2) India
  • 3) USA
Top 3 reserve holders
  • Unknown
Political stability of top producer 24.1
Political stability of top reserve holder Unknown
 

Glossary


Common oxidation states

The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Uncombined elements have an oxidation state of 0. The sum of the oxidation states within a compound or ion must equal the overall charge.


Isotopes

Atoms of the same element with different numbers of neutrons.


Key for isotopes


Half life
  y years
  d days
  h hours
  m minutes
  s seconds
Mode of decay
  α alpha particle emission
  β negative beta (electron) emission
  β+ positron emission
  EC orbital electron capture
  sf spontaneous fission
  ββ double beta emission
  ECEC double orbital electron capture

Oxidation states and isotopes

 
Common oxidation states 1
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  23Na 22.990 100
 

Glossary


Specific heat capacity (J kg−1 K−1)

Specific heat capacity is the amount of energy needed to change the temperature of a kilogram of a substance by 1 K.


Young's modulus

A measure of the stiffness of a substance. It provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.


Shear modulus

A measure of how difficult it is to deform a material. It is given by the ratio of the shear stress to the shear strain.


Bulk modulus

A measure of how difficult it is to compress a substance. It is given by the ratio of the pressure on a body to the fractional decrease in volume.


Vapour pressure

A measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure and temperature data – advanced

 
Specific heat capacity
(J kg−1 K−1)
1228 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) 6.3
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
0.000185 5.6 - - - - - - - - -
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History

Salt (sodium chloride, NaCl) and soda (sodium carbonate, Na2CO3) had been known since prehistoric times, the former used as a flavouring and preservative, and the latter for glass manufacture. Salt came from seawater, while soda came from the Natron Valley in Egypt or from the ash of certain plants. Their composition was debated by early chemists and the solution finally came from the Royal Institution in London in October 1807 where Humphry Davy exposed caustic soda (sodium hydroxide, NaOH) to an electric current and obtained globules of sodium metal, just as he had previously done for potassium, although he needed to use a stronger current.

The following year, Louis-Josef Gay-Lussac and Louis-Jacques Thénard obtained sodium by heating to red heat a mixture of caustic soda and iron filings.
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Podcasts

Listen to Sodium Podcast
Transcript :

Chemistry in its element: sodium


(Promo)

You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry.

(End promo)

Meera Senthilingam

This week an essential element with a split personality. Here's David Read.

David Read

Sodium, like most elements in the periodic table could be said to have a dual personality. On one side it is an essential nutrient for most living things, and yet, due to its reactive nature is also capable of wreaking havoc if you happen to combine it with something you shouldn't.

As such sodium is found naturally only in compounds and never as the free element. Even so it is highly abundant, accounting for around 2.6 per cent of the earths crust by weight. Its most common compounds include dissolved sodium chloride (or table salt), its solid form, halite and as a charge balancing cation in zeolites.

Aside from being an essential nutrient, the story of man and sodium is said to begin all the way back in the time of the Pharaohs in Ancient Egypt, with the first recorded mention of a sodium compound in the form of hieroglyphics. It is difficult to describe a pictogram through speech but imagine a squiggly line over the top of a hollow eye-shape, over the top of a semicircle, with a left-facing vulture image next to them all. This pictogram meant divine or pure and its name is the root of the word natron, which was used to refer to washing soda, or sodium carbonate decahydrate, as we would know it today. Sodium carbonate was used in soap, and also, in the process of mummification thanks to its water absorbing and bacteria killing pH control properties.

In medieval Europe, however, sodium carbonate was also used as a cure for headaches, and so took the name sodanum, from the Arabic suda, meaning headache. It was this terminology that inspired Sir Humphrey Davy to call the element sodium when he first isolated it by passing an electric current through caustic soda, or sodium hydroxide, in 1807. This process is known as electrolysis and using it Davy went on to isolate elemental potassium, calcium, magnesium and barium by a very similar method.

Chemistry teachers often confuse children when they tell them about chemical symbols. Whilst ones like H, N, C and O all seem perfectly logical, abbreviating sodium to Na seems counterintuitive at first. However, if we consider the word natron, we can see where the abbreviated form came from.

When isolated in metallic form, silvery white sodium is a violent element, immediately oxidising upon contact with air, and violently producing hydrogen gas which may burst into flame when brought into contact with water. It is one of the highly reactive group one elements that are named the alkali metals.

Like the other alkali metals, it has a very distinctive flame test - a bright orange colour, from the D-line emission. This is something you will have seen in all built up areas in the form of street lamps, which use sodium to produce the unnatural yellow light bathing our streets. This effect was first noted in 1860 by Kirchoff and Bunsen of Bunsen Burner fame.

Almost all young chemists will have done a flame test at some point, and sodium chloride is a popular choice. Unfortunately, the intensity of the colour is such that if any of the compound is spilled into the Bunsen burner, it is cursed to burn with a blue and orange speckled flame seemingly forever. The reaction of sodium with water is a favourite demonstration, and clips of it abound on the internet.

Sodium and its compounds have applications so diverse it would be impossible to mention them all here, a couple of examples include the fact that sodium is used to cool nuclear reactors, since it won't boil as water would at the high temperatures that are reached.

Sodium hydroxide can be used to remove sulfur from petrol and diesel, although the toxic soup of by-products that is formed has led to the process being outlawed in most countries. Sodium hydroxide is also used in biodiesel manufacture, and as a key component in products that remove blockages from drains.

Baking soda actually contains sodium (it's in the name!) and its chemical name is sodium bicarbonate, where I'm sure you've come across it in baking or cooking where it undergoes thermal decomposition at above 70°C to release carbon dioxide - which then makes your dough rise.

It is as an ion, however, that sodium really becomes important. An average human being has to take in around two grams of sodium a day - and virtually all of this will be taken in the form of salt in the diet. Sodium ions are used to build up electrical gradients in the firing of neurons in the brain. This involves sodium (and its big brother potassium) diffusing through cell membranes. Sodium diffuses in and is pumped back out, while potassium does the reverse journey. This can take up a huge amount of the body's energy - sometimes as much as 40 per cent.

I'd like to end with a brief story which highlights the dual personality of sodium. One man bought three and a half pounds of sodium metal from the internet and spent the evening reacting it with water in various shapes and sizes whilst he and his friends watched from a safe distance. The party was apparently a success, but he doesn't suggest hosting your own. The following day when the host came outside to check the area where he detonated the sodium was clear, he noticed that it was covered in swarms of yellow butterflies. After doing some research, he found that these butterflies had an interesting habit. The males search for sodium and gradually collect it, presenting it to their mates later as a ritual. So, that sums up the two faces of sodium. Its violent reactive nature contrasted with its use by amorous butterflies.

Meera Senthilingam

That was Southampton university's David Read with the two faced chemistry of sodium. Now next week, the chemical equivalent of train spotting.

Brian Clegg

It's easy to accuse the scientists who produce new, very heavy elements of being chemistry's train spotters. Just as train spotters spend hours watching for a particular locomotive so they can underline it in their book, it may seem that these chemists laboriously produce an atom or two of a superheavy element as an exercise in ticking the box. But element 114 has provided more than one surprise, showing why such elements are well worth investigating.

Meera Senthilingam

And to find out why element 114 is worth the effort join Brian Clegg in next week's Chemistry in its element.

(Promo)

Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld.org/elements.

(End promo)
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Resources

Description :
A series of short, fun videos exploring the chemistry of the alkali metals, taken from a lecture by Dr. Peter Wothers at the University of Cambridge.
Description :
A series of short, fun videos exploring the chemistry of the alkali metals, taken from a lecture by Dr. Peter Wothers at the University of Cambridge.
Description :
Many elements react with oxygen on heating. These reactions and the properties of their products illustrate the periodic nature of the elements.
Description :
An enlightening reaction!
Description :
Using laboratory tests identify sodium sulphate, sodium sulphite, sodium thiosulphate, sodium metabisulphite and sodium persulphate
Description :
A teaching resource on the group 1 flame tests, supported by video clips based around the Royal Institution 2012 Christmas Lectures®
 

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References

 
Visual Elements images and videos
© Murray Robertson 2011.

 

Data

W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
J. S. Coursey, D. J. Schwab, J.J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions(version 3.0), 2010, National Institute of Standards and Technology, Gaithersburg, MD, accessed December 2014.
T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954.

 

Uses and properties

John Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.
Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.
Periodic Table of Videos, accessed December 2014.

 

Supply risk data

Derived in part from material provided by the British Geological Survey © NERC.

 

History text

© John Emsley 2012.

 

Podcasts

Produced by The Naked Scientists.

 

Periodic Table of Videos

Created by video journalist Brady Haran working with chemists at The University of Nottingham.