inorganic chemistry powerpoint
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Presentation.pptxGroup 2 Elements (Chapter 12)
Mashfiq Ahmed CHE-111
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Introduction
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Figure 1. The Group 2 elements on the Periodic Table.
Calcium, strontium, barium, and radium are known as alkaline earth metals, but the term is often applied to the whole of Group 2.
Silvery white metals, bonding is normally ionic
Denser, harder, and less reactive than Group 1 elements
Reference: [2]
The Elements
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The smaller atomic radii compared to Group 1 leads to higher densities and ionization energies. As the ionization energy decreases, the atomic radii increases and the elements become more reactive and electropositive.
Reference: [2]
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Simple Compounds
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All of the elements occur as M(II) in their simple compounds and apart from Be, the compounds are predominantly ionic.
Group 2 elements form ionic hydrides such as MgH2 while beryllium forms BeH4.
All the elements form halides, MX2, by direct combination of the elements.
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Anomalous Properties of Beryllium
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The small size of Be2+, high charge density, and polarizing power results in Be being largely covalent and its ion is a strong Lewis Acid.
There is a significant covalent contribution to the bonding in compounds such as beryllium halides.
Be has a greater tendency to form complexes with the formation of molecular compounds, such as Be4O(O2CCH3)6.
Be forms many stable organometallic compounds, including methylberyllium and beryllocene ((C5H5)2Be).
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Anomalous Properties of Beryllium
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Be has a strong diagonal relationship with Al.
Both form covalent hydrides and halides
Their oxides are amphoteric while the rest of the Group 2 oxides are basic.
Reference: [2]
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Occurrence and Extraction
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Beryllium occurs naturally as the mineral beryl Be2Al2(SiO3)6 which is the basis of emerald.
Beryllium is extracted by heating beryl with sodium hexafluorosilicate, Na2SiF6, to produce BeF2 which is then reduced to magnesium.
Reference: [3]
Figure 2. Emerald beryl.
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Occurrence and Extraction
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Magnesium is also extracted from dolomite when heated in air.
Calcium, strontium, and barium are extracted by electrolysis of their respective molten chlorides.
Figure 3. Dolomite crystals.
Reference: [4]
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Occurrence and Extraction
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Figure 4. Pitchblende or uraninite.
Reference: [5]
All isotopes of radium are radioactive and undergo decay with half-lives from 42 minutes to 1599 years.
It can be extracted from the uranium-bearing mineral pitchblende.
1 g of Ra for 10 tons of pitchblende
How to extract radium:
It involved many steps in which the ore was ground, dissolved in acids and other liquids, separated or filtered, and tested for radioactivity. Once they had a residue which was more radioactive than the material that they started with, they repeated the process.
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Uses of the Elements and their Compounds
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Reference: [6]
Beryllium is resistant to corrosion and is one of the lightest metals so it’s used in precision instruments, aircrafts, and missiles.
Magnesium is also used in the construction of aircrafts since it can form light alloys, especially with aluminum.
Mg is also used in fireworks and flares because it burns in the air and produces an intense, white flame.
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Uses of the Elements and their Compounds
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Reference: [7]
Calcium oxide is a major component of cement and is used in steelmaking and papermaking.
Calcium sulfate dihydrate, CaSO4 · 2H2O, is used in building materials such as plasterboard and CaSO4 is a common drying agent.
Strontium is used in pyrotechnics and in glasses for color television tubes.
Compounds of calcium are much more useful than the element itself.
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Uses of the Elements and their Compounds
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Reference: [7]
Barium compounds are effective at absorbing X-rays due to the large number of electrons in Ba2+. Barium sulfate, or barium meal, is used to investigate the intestinal tract.
Radium-223 is sometimes used to treat prostate cancer.
Barium carbonate is used for rat poison. Radium is highly radioactive and has very few uses today. It used to be used in luminous paints but that’s considered to be too hazardous.
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Hydrides
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The Group 2 elements form ionic, saline hydrides with the exception of Be.
The ionic hydrides of the heavier elements react violently with water to produce hydrogen.
The reaction is not as violent as the Group 1 elements and can be used as a source of hydrogen in fuel cells.
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Halides
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All the Group 2 fluorides with the exception of BeF2 are insoluble in water and the solubility increases slightly as you move down the group.
All other halides are soluble.
CaF2 is the most important fluoride in Group 2 since its mineral form, fluorite, is the only large-scale source of fluorine.
MgCl2 is the most important chloride for industry as it’s used for the production of magnesium metal.
CaCl2 is used as a laboratory drying agent and to de-ice roads.
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Oxides
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All Group 2 elements form normal oxides with oxygen except Ba, which forms a peroxide.
Beryllium oxide has a high melting point (2570°C), low reactivity, and excellent thermal conductivity, the highest of any oxide. It’s obtained through the ignition of Be in oxygen.
The other Group 2 elements are more commonly obtained by decomposition of the carbonates:
The melting points of these oxides decrease down the group as the lattice enthalpies decrease with increasing cation radius.
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Solubility
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With the exception of fluorides, the salts of singly charged anions are usually soluble in water.
Doubly charged anions (such as oxides) are usually only sparingly soluble due to the high lattice enthalpy arising from the high charge of the anion.
The insolubility is responsible for the deposits of magnesium and calcium minerals like limestone and dolomite.
Going down the group, the ions become less hard and the fluorides and hydroxides (small, hard anions) are insoluble for the harder Be2+ and Mg2+ but more soluble for Ba2+.
Group 2 compounds are much less soluble than Group 1 compounds.
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Organometallic Compounds
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Organometallic compounds of Be are pyrophoric in air and unstable in water.
Methylberyllium can be prepared by transmetallation from methylmercury in a hydrocarbon solvent:
Grignard reagents in ether can also be used in the synthesis of organoberyllium compounds:
Prepared from Mg metal and an organohalide, grignard reagents are widely used in synthetic organic chemistry.
The organometallic compounds of Ca, Sr, and Ba are generally ionic and very unstable.
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References
Martín, Cindy Paola Pinzón. “The Groups of the Periodic Table.” Chemistry, chemistrycppm.blogspot.com/2016/02/the-groups-of-periodic-table.html.
Shriver, Duward. Inorganic Chemistry. 6th ed., W. H. Freeman, 2014.
“Beryl.” Geology, Geology.com, geology.com/minerals/beryl.shtml.
“Dolomite.” Geology, Geology.com, http://geology.com/minerals/dolomite.shtml
“Uraninite Var Pitchblende.” e-Rocks, e-Rocks.com, e-rocks.com/item/mnr122989/uraninite-var-pitchblende.
“Magnesium.” Royal Society of Chemistry, www.rsc.org/periodic-table/element/12/magnesium.
“Strontium.” Google Sites, sites.google.com/site/strontiumkz/applications.
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