- Chemical properties
- Ionic character
- Metal links
- Reactions
- Reaction with water
- Reaction with oxygen
- Reaction with halogens
- Applications
- Beryllium
- Magnesium
- Calcium
- Strontium
- Barium
- Radio
- References
The alkaline earth metals are those that make up group 2 of the periodic table, and are indicated in the purple column in the image below. From top to bottom, they are beryllium, magnesium, calcium, strontium, barium, and radium. An excellent mnemonic method to remember their names is through the pronunciation of Mr. Becamgbara.
Breaking down the letters of Mr. Becamgbara, you have that "Sr" is strontium. «Be» is the chemical symbol for beryllium, «Ca» is the symbol for calcium, «Mg» is that of magnesium, and «Ba» and «Ra» correspond to the metals barium and radium, the latter being an element of nature. radioactive.
The term "alkaline" refers to the fact that they are metals capable of forming very basic oxides; and on the other hand, "terrestrial" refers to land, a name given because of its low solubility in water. These metals in their pure state present similar silvery colorations, covered by grayish or black oxide layers.
The chemistry of alkaline earth metals is very rich: from their structural participation in many inorganic compounds to the so-called organometallic compounds; These are those that are interacting by covalent or coordination bonds with organic molecules.
Chemical properties
Physically, they are harder, dense and resistant to temperatures than alkali metals (those of group 1). This difference resides in their atoms, or what is the same, in their electronic structures.
As they belong to the same group on the periodic table, all their congeners exhibit chemical properties that identify them as such.
Why? Because their valence electron configuration is ns 2, which means that they have two electrons to interact with other chemical species.
Ionic character
Due to their metallic nature, they tend to lose electrons to form divalent cations: Be 2+, Mg 2+, Ca 2+, Sr 2+, Ba 2+, and Ra 2+.
In the same way that the size of its neutral atoms varies as it descends through the group, its cations also get larger, going down from Be 2+ to Ra 2+.
As a result of their electrostatic interactions, these metals form salts with the most electronegative elements. This high tendency to form cations is another chemical quality of alkaline earth metals: they are very electropositive.
Large atoms react more easily than small ones; in other words, Ra is the most reactive metal and Be the least reactive. This is the product of the less attractive force exerted by the nucleus on increasingly distant electrons, now with a greater probability of "escaping" to other atoms.
However, not all compounds are ionic in nature. For example, beryllium is very small and has a high charge density, which polarizes the electron cloud of the neighboring atom to form a covalent bond.
What consequence does that bring? That beryllium compounds are predominantly covalent and non-ionic, unlike the others, even if it is the Be 2+ cation.
Metal links
By having two valence electrons, they can form more charged "electron seas" in their crystals, which integrate and group metal atoms more closely in contrast to alkali metals.
However, these metallic bonds are not strong enough to give them outstanding hardness characteristics, they are actually soft.
Also, these are weak compared to those of transition metals, reflected in their lower melting and boiling points.
Reactions
The alkaline earth metals are very reactive, which is why they do not exist in nature in their pure states, but are linked in various compounds or minerals. The reactions behind these formations can be summarized generically for all members of this group
Reaction with water
They react with water (with the exception of beryllium, due to its "toughness" in offering its pair of electrons) to produce corrosive hydroxides and hydrogen gas.
M (s) + 2H 2 O (l) => M (OH) 2 (aq) + H 2 (g)
The hydroxides of magnesium -Mg (OH) 2 - and of berili -Be (OH) 2 - are poorly soluble in water; furthermore, the second of them is not very basic, since the interactions are covalent in nature.
Reaction with oxygen
They burn in contact with oxygen in the air to form the corresponding oxides or peroxides. Barium, the second largest metal atoms, forms the peroxide (BaO 2), which is more stable because the ionic radii Ba 2+ and O 2 2- are similar, strengthening the crystalline structure.
The reaction is as follows:
2M (s) + O 2 (g) => 2MO (s)
Therefore, the oxides are: BeO, MgO, CaO, SrO, BaO and RaO.
Reaction with halogens
This corresponds to when they react in an acid medium with the halogens to form inorganic halides. This has the general chemical formula MX 2, and among these are: CaF 2, BeCl 2, SrCl 2, BaI 2, RaI 2, CaBr 2, etc.
Applications
Beryllium
Given its inert reactivity, beryllium is a metal with high resistance to corrosion, and added in small proportions to copper or nickel, it forms alloys with mechanical and thermal properties interesting for different industries.
Among these are those that work with volatile solvents, in which the tools must not produce sparks due to mechanical shocks. Likewise, its alloys find use in the manufacture of missiles and materials for aircraft.
Magnesium
Unlike beryllium, magnesium is friendlier to the environment and is an essential part of plants. For this reason it is of high biological importance and in the pharmaceutical industry. For example, milk magnesia is a remedy for heartburn and consists of a solution of Mg (OH) 2.
It also has industrial applications, such as in welding of aluminum and zinc alloys, or in the production of steels and titanium.
Calcium
One of its main uses is due to CaO, which reacts with aluminosilicates and calcium silicates to give cement and concrete their desired properties for construction. Likewise, it is a fundamental material in the production of steel, glass and paper.
On the other hand, CaCO 3 participates in the Solvay process to produce Na 2 CO 3. For its part, CaF 2 finds use in the manufacture of cells for spectrophotometric measurements.
Other calcium compounds are used in the manufacture of food, personal hygiene products, or cosmetics.
Strontium
When burning, strontium flashes an intense red light, which is used in pyrotechnics and to make sparklers.
Barium
Barium compounds absorb X-rays, so BaSO 4 -which is also insoluble and prevents the toxic Ba 2+ from roaming free in the body- is used to analyze and diagnose alterations in digestive processes.
Radio
Radium has been used in the treatment of cancer because of its radioactivity. Some of its salts were used to color watches, and this application was later prohibited because of the risks for those who wore them.
References
- Helmenstine, Anne Marie, Ph.D. (June 7, 2018). Alkaline Earth Metals: Properties of Element Groups. Retrieved on June 7, 2018, from: thoughtco.com
- Mentzer, AP (May 14, 2018). Uses of Alkaline Earth Metals. Sciencing. Retrieved on June 7, 2018, from: sciencing.com
- What are the uses of alkaline earth metal? (October 29, 2009). eNotes. Retrieved on June 7, 2018, from: enotes.com
- Advameg, Inc. (2018). Alkaline earth metals. Retrieved on June 7, 2018, from: scienceclarified.com
- Wikipedia. (2018). Alkaline earth metal. Retrieved on June 7, 2018, from: en.wikipedia.org
- Chemistry LibreTexts. (2018). The Alkaline Earth Metals (Group 2). Retrieved on June 7, 2018, from: chem.libretexts.org
- Chemical Elements. (2009, August 11). Beryllium (Be).. Retrieved on June 7, 2018, from: commons.wikimedia.org
- Shiver & Atkins. (2008). Inorganic chemistry. In The elements of group 2. (Fourth edition.). Mc Graw Hill.