SafekipediaAlkaline earth metal
Adapted from Wikipedia · Adventurer experience
Alkaline earth metals are six chemical elements found in group 2 of the periodic table. These elements are beryllium, magnesium, calcium, strontium, barium, and radium. They all look shiny and silvery-white and can react easily.
These elements have a special way their electrons are arranged. They can lose two electrons to form ions with a charge of +2 and an oxidation state of +2. Although helium is usually with noble gases, it might share some traits with beryllium under some conditions.
All of these elements are found in nature, except radium, which is made when uranium and thorium break down. Scientists have tried but have not been able to make element 120, which could be the next member of this group.
Characteristics
The alkaline earth metals are six elements in group 2 of the periodic table. They are shiny, silvery-white, and somewhat reactive metals. These elements include beryllium, magnesium, calcium, strontium, barium, and radium.
These metals share many similar properties. They are soft and have low densities, melting points, and boiling points. They react with certain elements to form new compounds. For example, they react with halogens to make ionic compounds and with water to produce alkaline solutions, though beryllium does not react with water easily. These metals also have low ionization energies, meaning they can lose electrons easily to form ions.
| Metal | M2+ hydration (-MJ/mol) | "MF2" unit hydration (-MJ/mol) | MF2 lattice (-MJ/mol) | Solubility (mol/kL) |
|---|---|---|---|---|
| Be | 2.455 | 3.371 | 3.526 | soluble |
| Mg | 1.922 | 2.838 | 2.978 | 1.2 |
| Ca | 1.577 | 2.493 | 2.651 | 0.2 |
| Sr | 1.415 | 2.331 | 2.513 | 0.8 |
| Ba | 1.361 | 2.277 | 2.373 | 6 |
| Alkaline earth metal | Standard atomic weight (Da) | Melting point (K) | Melting point (°C) | Boiling point (K) | Boiling point (°C) | Density (g/cm3) | Electronegativity (Pauling) | First ionization energy (kJ·mol−1) | Covalent radius (pm) | Flame test color | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Beryllium | 9.012182(3) | 1560 | 1287 | 2744 | 2471 | 1.845 | 1.57 | 899.5 | 105 | White | |
| Magnesium | 24.3050(6) | 923 | 650 | 1363 | 1090 | 1.737 | 1.31 | 737.7 | 150 | Brilliant-white | |
| Calcium | 40.078(4) | 1115 | 842 | 1757 | 1484 | 1.526 | 1.00 | 589.8 | 180 | Brick-red | |
| Strontium | 87.62(1) | 1050 | 777 | 1655 | 1382 | 2.582 | 0.95 | 549.5 | 200 | Crimson | |
| Barium | 137.327(7) | 1000 | 727 | 2170 | 1897 | 3.594 | 0.89 | 502.9 | 215 | Apple-green | |
| Radium | 969 | 696 | 2010 | 1737 | 5.502 | 0.9 | 509.3 | 221 | Crimson red | ||
History
The alkaline earth metals are named after special compounds called alkaline earths. Early scientists called these compounds "earths" because they did not dissolve in water and could resist heat. Later, a scientist named Antoine Lavoisier realized these "earths" were actually made from metals.
The first person to get these metals in pure form was Humphry Davy in 1808. He used a process called electrolysis to separate the metals from their compounds. This showed that the "earths" were linked to metals.
People have known about some of these metals for a very long time. For example, calcium has been used in building since ancient times. Magnesium was discovered in 1618, strontium in 1790, and the last one, radium, was found in 1898 by Marie and Pierre Curie. They noticed that some materials stayed radioactive after uranium decayed, which led to the discovery of radium.
Occurrence
Beryllium is found in very small amounts in the Earth’s crust and water. It is rare in seawater but a bit more common in freshwater.
Magnesium and calcium are much more common in the Earth’s crust. They are found in minerals such as carnallite, magnesite, dolomite, chalk, limestone, gypsum, and anhydrite. Strontium is also found in minerals like celestite and strontianite, while barium is often in the mineral barite.
Radium is a decay product of uranium and is found in uranium-bearing ores. It changes quickly, so the radium we find today comes from the slower decay of uranium.
Production
The six alkaline earth metals can be made in many ways.
Beryllium is taken from beryllium hydroxide. It can be made by mixing beryl with sodium fluorosilicate and soda at high heat. This makes sodium fluoroberyllate, which can be turned into beryllium hydroxide. Another way is to heat beryl, cool it with water, and treat it with sulfuric acid to get beryllium hydroxide. From there, beryllium can be made.
Strontium is taken from the mineral celestite. This can be done by mixing celestite with sodium carbonate, or by using coal.
Barium is made from barite, which is impure barium sulfate. It is turned into barium sulfide using coke. This can be used to make pure barium sulfate or other compounds like barium nitrate. These are heated to make barium oxide, which can be turned into pure barium. China makes more than half of the world's barium.
Magnesium is often made from magnesite or dolomite. Dolomite is crushed, roasted, and mixed with seawater. This makes magnesium hydroxide, which is turned into magnesium chloride. Electrolysis of this produces magnesium.
Calcium is found in the Earth's crust as calcium carbonate. China and Russia make most of the world's calcium, using a method with electrolysis of calcium chloride. The U.S. and Canada also make calcium by reducing lime with aluminium at high heat.
Radium was first made by Marie Skłodowska-Curie from materials left after uranium was taken out. Today, radium is taken from used reactor materials. Pure radium metal can be made by heating it with aluminium in a vacuum.
Main article: Beryllium § Extraction
Main article: Strontium § Production
Main article: Barium § Occurrence and production
Main article: Magnesium § Production
Main article: Calcium § Occurrence and production
Main article: Radium § Production
Applications
Beryllium is used in military and electronic devices. It helps make materials strong and able to carry heat. It is also used in special tools.
Magnesium is used to build strong parts. It is mixed with other metals to make it stronger. It also helps make iron and steel, and is used in making titanium.
Calcium helps separate metals from rocks. It is used in making cheese, mortar, and cement.
Strontium and barium have fewer uses. Strontium makes red fireworks. Barium helps keep vacuum tubes clean and is used in oil industries.
Radium used to be used in glow-in-the-dark paints but is no longer used because it can make people sick.
Representative reactions of alkaline earth metals
Alkaline earth metals can react in many ways with other substances. For example, when calcium meets chlorine gas, it forms calcium chloride. This calcium chloride can absorb water from the air and dissolve in it.
These metals react with oxygen to make oxides. Calcium and magnesium both make oxides when they meet oxygen. They can also react with sulfur and carbon to form other compounds. Some, like beryllium and magnesium, can react directly with nitrogen.
When these metals meet water, they can make a hydroxide and hydrogen gas. However, beryllium and magnesium might not react easily because of a layer on their surface. In some conditions, magnesium can still react with water vapor.
Alkaline earth metals can react with acids to form salts and hydrogen gas. Beryllium, for example, reacts with hydrochloric acid to make beryllium chloride and hydrogen gas. Some of these metals can dissolve in strong bases, showing special chemical properties.
Identification of alkaline earth cations
The flame test can show the color some alkaline earth metals add to a flame when heated. But beryllium and magnesium do not change the flame color because they are very small.
When testing in a liquid, alkaline earth metals react in special ways:
- Magnesium ions (Mg2+) form a white solid when mixed with disodium phosphate, ammonium salts, and ammonia.
- Calcium ions (Ca2+) create a white solid when mixed with ammonium oxalate.
- Strontium ions (Sr2+) form a white solid when mixed with soluble sulfate salts.
All of these metal ions also make a white solid when mixed with ammonium carbonate, ammonium chloride, and ammonia.
| Metal | Colour |
|---|---|
| Ca | Brick-red |
| Sr | Crimson red |
| Ba | Green/Yellow |
| Ra | Carmine red |
Compounds of alkaline earth metals
Alkaline earth metals can form many kinds of compounds.
One type is called oxides. These oxides are made when some carbonates are heated. For example, heating calcium carbonate makes calcium oxide and carbon dioxide.
These oxides can also be made in labs from hydroxides or nitrates. They show basic properties because they change the color of some testing liquids. When these oxides mix with water, they create hydroxides.
Another kind of compound is hydroxides. These are made when oxides mix with water. Most hydroxides also show basic properties, but beryllium hydroxide is different.
Salts are another type of compound. Calcium and magnesium are found in many natural salts, like in rocks and hard water. Hard water can be softened by using special materials.
Biological role and precautions
Magnesium and calcium are very important for all living things. They help in many processes inside cells and are part of our bones.
Strontium is important for sea life, especially corals, which use it to build their hard shells. Strontium and barium have some uses in medicine, like in special X-ray tests. However, too much strontium-90 can be harmful because it is radioactive and acts like calcium, building up in bones and harming bone marrow.
Beryllium and radium are both harmful. Beryllium does not usually get into living things and can be very toxic if it does. Radium is also toxic because it is radioactive and not easily found in nature.
Extensions
The next alkaline earth metal after radium might be element 120, but this is not certain. Scientists tried to make element 120 in 2007 by mixing different materials, but they could not find it.
Element 120 is expected to behave more like calcium or strontium than barium or radium. This would be different from normal patterns because the energy levels of element 120’s outer electrons might make it less reactive.
It is unclear what the next alkaline earth metal after element 120 could be. Some ideas suggest it might be element 166, but its properties might put it in a different group.
Related articles
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