Magnesium metal. Image by Maral10.
Data Zone
| Classification: | Magnesium is an alkali earth metal |
| Color: | silvery-white |
| Atomic weight: | 24.305 |
| State: | solid |
| Melting point: | 650 oC, 923 K |
| Boiling point: | 1090 oC, 1363 K |
| Electrons: | 12 |
| Protons: | 12 |
| Neutrons in most abundant isotope: | 12 |
| Electron shells: | 2,8,2 |
| Electron configuration: | 1s2 2s2 2p6 3s2 |
| Density @ 20oC: | 1.738 g/cm3 |
| Atomic volume: | 13.97 cm3/mol |
| Structure: | hcp: hexagonal close packed |
| Hardness: | 2.5 mohs |
| Specific heat capacity | 1.02 J g-1 K-1 |
| Heat of fusion | 8.48 kJ mol-1 |
| Heat of atomization | 146 kJ mol-1 |
| Heat of vaporization | 127.4 kJ mol-1 |
| 1st ionization energy | 737.7 kJ mol-1 |
| 2nd ionization energy | 1450.6 kJ mol-1 |
| 3rd ionization energy | 7732.6 kJ mol-1 |
| Electron affinity | 78 kJ mol-1 |
| Minimum oxidation number | 0 |
| Min. common oxidation no. | 0 |
| Maximum oxidation number | 2 |
| Max. common oxidation no. | 2 |
| Electronegativity (Pauling Scale) | 1.31 |
| Polarizability volume | 10.6 Å3 |
| Reaction with air | vigorous, w/ht ⇒ MgO, Mg3N2 |
| Reaction with 15 M HNO3 | vigorous ⇒ NOx, Mg(NO3)2 |
| Reaction with 6 M HCl | mild ⇒ H2, MgCl2 |
| Reaction with 6 M NaOH | none |
| Oxide(s) | MgO |
| Hydride(s) | MgH2 |
| Chloride(s) | MgCl2 |
| Atomic radius | 150 pm |
| Ionic radius (1+ ion) | – |
| Ionic radius (2+ ion) | 86 pm |
| Ionic radius (3+ ion) | – |
| Ionic radius (1- ion) | – |
| Ionic radius (2- ion) | – |
| Ionic radius (3- ion) | – |
| Thermal conductivity | 156 W m-1 K-1 |
| Electrical conductivity | 22.4 x 106 S m-1 |
| Freezing/Melting point: | 650 oC, 923 K |
Joseph Black was investigating magnesia alba (magnesium carbonate) as a cure for indigestion when he made his chemical discoveries. Milk of magnesia, made with magnesium hydroxide, is now used to relieve indigestion. The hydroxide has an advantage over Black’s carbonate: its reaction with stomach acid (HCl) doesn’t release carbon dioxide, so it doesn’t cause belching. It does, however, form magnesium chloride, which is a laxative.
Magnesium gives intense, white light in fireworks.
Should I use carbon dioxide to extinguish a magnesium fire?
Is it a good idea to extinguish burning magnesium with water?
Discovery of Magnesium
Magnesium and calcium were once thought to be the same substance. In 1755 Scottish chemist Joseph Black showed by experiment that the two were different. Black wrote:
“We have already shewn by experiment, that magnesia alba [magnesium carbonate] is a compound of a peculiar earth and fixed air.” (1)
Magnesium was first isolated by Sir Humphrey Davy in 1808, in London, England. Davy had built a large battery and used it to pass electricity through salts. In doing so, he discovered or isolated for the first time several alkali and alkali earth metals.
In magnesium’s case, Davy’s method was similar to the one he used for barium, calcium and strontium.
Davy made a paste of moist magnesium oxide and red mercury oxide. (2)
He made a depression in the paste and placed about 3.5 grams of mercury metal there to act as the negative electrode. He used platinum as the positive electrode. Davy did the experiment under naphtha (a liquid hydrocarbon under which he had found he could safely store potassium and sodium).
When electricity was passed through the paste, a magnesium-mercury amalgam formed at the mercury electrode. (In later experiments Davy used moist magnesium sulfate instead of the oxide and obtained the amalgam much faster.) (2a)
The mercury was then removed from the amalgam by heating to leave magnesium metal. (2)
In a lecture to the Royal Society in June 1808, Davy described how the magnesium he obtained was not pure because of difficulties in removing the mercury entirely from the magnesium. He was, however, able to observe that in air the metal turned into a white powder, gaining weight as it reacted with oxygen and returned to its oxide form. (2b)
Davy thought the logical name for the new metal was ‘magnesium’ but instead called it ‘magnium.’
He thought the name ‘magnium’ was, “objectionable, but magnesium has been already applied to metallic manganese…”
By 1812, Davy had changed his mind, following the “candid criticisms of some philosophical friends,” and the new metal became known as magnesium, while metallic manganese became known as… manganese. (3)
Magnesium’s name is derived from magnesia, which Davy used in his experiment. Magnesia is the district of Thessaly in Greece where magnesia alba [magnesium carbonate] was found.
In France, in 1830, Antoine Bussy published his work showing how pure magnesium metal could be obtained. Bussy had read Friedrich Wöhler’s 1828 publication of how he had produced pure aluminum by reacting aluminum chloride with potassium. By analogy, Bussy thought he could do something similar to produce pure magnesium from magnesium chloride; he was correct.
Under red heat he reacted magnesium chloride with potassium vapor and obtained pure magnesium. He wrote, “The metal is silvery white, very brilliant, very malleable, flattens into flakes under a hammer… dilute acids attack the metal, releasing hydrogen.” (4)
Interesting Facts about Magnesium
- At the center of every chlorophyll molecule, in every green plant, there is a magnesium ion.
- Magnesium is one of the two dozen or so elements that are essential for life. Magnesium is vital in human metabolism, needed for over 300 biochemical reactions.
- Magnesium fires must be treated with caution. Adding water to them produces hydrogen, which makes the fire burn even more fiercely.
- If you try to put out a magnesium fire with carbon dioxide, you’ll also find yourself out of luck: magnesium burns in both pure nitrogen and pure carbon dioxide, and a carbon dioxide fire-extinguisher will feed a magnesium fire.
- Mag wheels were once made of a magnesium alloy: magnesium is both light and strong. Mag wheels no longer include magnesium; the wheels did not last well and potentially were a fire hazard.
Despite the absence of magnesium, the wheels have kept their original name. - Magnesium is formed in stars with a mass of eight or more Earth suns.
Near the end of their lives, these stars enter the carbon burning phase, also making oxygen, sodium and neon. - Magnesium is the second most abundant metal in seawater. (Only sodium is more abundant.)
- Our bodies need the correct amount of magnesium in our diets for us to sleep properly. If it’s too high or too low, we can suffer from sleep disturbance.
- About 13% of our planet’s entire mass comes from magnesium. This means there’s enough magnesium within Earth to make a planet of the same mass as Mars AND have enough magnesium left over to make three more objects of the same mass as our moon.
- There is a significantly higher proportion of magnesium below Earth’s crust than in it.
Magnesium compounds are needed for over 300 biochemical reactions in the human body. Many of us don’t get enough of it. Pumpkin seeds are a great source of magnesium.
A molecular model of the business end of a chlorophyll molecule. Magnesium is colored orange; nitrogen blue; oxygen red; carbon dark gray; and hydrogen light gray. Image by Diplodocus.
Appearance and Characteristics
Harmful effects:
Magnesium powder is an explosive hazard.
The bright white light plus ultraviolet from burning magnesium can cause permanent eye damage.
Characteristics:
Magnesium is a silvery-white, low density, reasonably strong metal that tarnishes in air to form a thin oxide coating. Magnesium and its alloys have very good corrosion resistance and good high temperature mechanical properties.
The metal reacts with water to produce hydrogen gas.
When it burns in air, magnesium produces a brilliant white light.
Uses of Magnesium
The brilliant light it produces when ignited is made use of in photography, flares, pyrotechnics and incendiary bombs.
With a density of only two-thirds that of aluminum, and just over one-fifth that of iron, magnesium alloys are used in aircraft, car engine casings, and missile construction.
The metal is widely used in the manufacturing of mobile phones, laptop computers, cameras, and other electronic components.
Organic magnesium compounds (Grignard reagents) are important in the synthesis of organic molecules.
Magnesium compounds such as the hydroxide (milk of magnesia, Mg(OH2)), sulfate (Epsom salts), chloride and citrate are used for medicinal purposes.
Magnesium is the second most important intracellular cation and is involved in a variety of metabolic processes including glucose metabolism, ion channel translocation, stimulus-contraction coupling, stimulus secretion coupling, peptide hormone receptor signal transduction. (5)
Abundance and Isotopes
Abundance earth’s crust: 2.3 % by weight, 2.0 % by moles
Abundance solar system: 700 parts per million by weight, 30 parts per million by moles
Cost, pure: $3.7 per 100g
Cost, bulk: $0.29 per 100g
Source: Magnesium is the eighth most abundant element in the Earth’s crust and the sixth most abundant metal. Magnesium is obtained commercially by the ‘Pidgeon’ process. This high temperature method uses silicon as a reducing agent to extract magnesium from minerals such as dolomite (MgCa(CO 3)2) or magnesite (MgCO 3) or saltwater.
Isotopes: Magnesium has 15 isotopes whose half-lives are known with mass ranges from 20 to 34. Naturally occurring magnesium is a mixture of its three stable isotopes and they are found in the percentages shown: 24Mg (79.0%), 25Mg (10.0%) and 26Mg (11.0%).
References
1. Joseph Black, Experiments upon Magnesia Alba, Quick-Lime, and some other Alkaline Substances (1756)
2. John Davy (Editor), The Collected Works of Sir Humphry Davy, Vol V, 1840, p111 Smith, Elder and Co. Cornhill.
2a. John Davy (Editor), The Collected Works of Sir Humphry Davy, Vol V, 1840, p110 Smith, Elder and Co. Cornhill.
2b. John Davy (Editor), The Collected Works of Sir Humphry Davy, Vol V, 1840, p115 Smith, Elder and Co. Cornhill.
3. Sir Humphry Davy, Elements of Chemical Philosophy., 1812, Part 1, Vol. 1, p198.
4. Gay-Lussac et al, Annals of Chemistry and Physics, 1831, Vol. XLVI, p434-437.
5. Nancy E. Bernhardt, Artur M. Kasko, Nutrition for the Middle Aged and Elderly., (2008) p333. Nova Science Publishers
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Loved the site very helpful but one thing I suggest is that you should put like the family of [element] that would be extremely helpful
Thanks AJ. Rather than family, we use the word classification (see the Data Zone at the top of this page):
Classification: Magnesium is an alkali earth metal.