3. 2 elements are silvery white metals and the bonding in their compounds is
normally described in terms of the ionic model. Some aspects of the chemical
properties of beryllium are more like those of a metalloid with a degree of
covalence in its bonding. The elements are denser, harder, and less reactive
than the elements of Group 1 but are still more reactive than many typical
metals. The lighter elements beryllium and magnesium form a number
of complexes and organometallic compounds.
4. Discovery of Grp 2
Metals
• The English chemist Sir Humphry Davy first
isolated Mg, Ca, Sr, and Ba in 1808 by means of
electrolysis.
• (Mg was originally called magnium since Davy
had already applied the word "magnesium" to the
element manganese.)
• Be was initially isolated from beryl by the French
chemist Antoine Bussy and independently in
Germany by Friedrich Wöhler in 1828.
• The discovery of Radium did not occur until 1898
when Marie and Pierre Curie purified it from
barium using its radioactivity. They named it from
the Latin word radius (meaning "ray") because
the strength of its radioactivity was more than a
million times that of uranium.
5. Occurrence and Extraction of Alkaline Earth
Metal
Beryllium occurs naturally as the semiprecious mineral beryl,
Be3Al2(SiO3)6.
Magnesium is the eighth most abundant element in the Earth’s
crust and the third most abundant element dissolved in seawater; it
is commercially extracted from seawater and the mineral
dolomite, CaCO3.MgCO3.
Calcium is the fifth most abundant element in the Earth’s crust but
only the seventh most common in seawater due to the low
solubility of CaCO3; it occurs widely in its carbonate as limestone,
marble, and chalk, and it is a major component of biominerals, such
as shells and coral.
Calcium, strontium, and barium are all extracted by electrolysis of
their molten chlorides.
Radium can be extracted from uranium-bearing minerals although
all its isotopes are radioactive.
6. Properties of Group 2
Metals
• They have ns2 valence-shell electron
configurations and can therefore lose two
electrons to form doubly positive ions: M2+
. Because their first ionization energy is
larger than that of alkali metals, the group
2A metals are somewhat less reactive
than alkali metals. The general reactivity
trend is: Ba > Sr > Ca
> Mg > Be. Found in nature only in salts,
not in the elemental state.
8. Physical
Properties
Harder than Group 1 metals but are still
relatively soft, silvery metals. Higher
melting points, densities and ionisation
energies than alkali metals. Beryllium has
different physical properties from other
Group 2 elements. E.g., it has a higher
melting point and is much harder than the
others.
12. Application
s
• Beryllium is used mostly for military applications, but
there are other uses of beryllium, as well. In electronics,
beryllium is used as a p-type dopantin some
semiconductors,and beryllium oxide is used as a high-
strength electrical insulator and heat conductor. Due to
its light weight and other properties, beryllium is also
used in mechanics when stiffness, light weight, and
dimensional stability are required at wide temperature
ranges.
• Magnesium has many different uses. One of its most
common uses was in industry, where it has many
structural advantages over other materials such as
aluminium, although this usage has fallen out of favor
recently due to magnesium's flammability. Magnesium is
also often alloyed with aluminium or zinc to form
materials with more desirable properties than any pure
metal. Magnesium has many other uses in industrial
applications, such as having a role in the production of
iron and steel, and the production of titanium.
13. Applications
continued
• Calcium also has many uses. One of its uses is as a reducing agent in the
separation of other metals from ore, such as uranium. It is also used in
the production of the alloys of many metals, such as aluminium and
copper alloys, and is also used to deoxidize alloys as well. Calcium also
has a role in the making of cheese, mortars, and cement.
• Strontium and barium do not have as many applications as the lighter
alkaline earth metals, but still have uses. Strontium carbonate is often
used in the manufacturing of red fireworks, and pure strontium is used in
the study of neurotransmitter release in neurons. Barium has some use in
vacuum tubes to remove gases,and barium sulfate has many uses in the
petroleum industry, as well as other industries.
• Due to its radioactivity, radium no longer has many applications, but it
used to have many. Radium used to be used often in luminous paints,
although this use was stopped after workers got sick. As people used to
think that radioactivity was a good thing, radium used to be added to
drinking water, toothpaste, and many other products, although they are
also not used anymore due to their health effects. Radium is no longer
even used for its radioactive properties, as there are more powerful and
safer emitters than radium.
14. Some Reactions of Alkaline Earth
Metals
Oxides of the alkaline earth metals are basic oxides and have all properties of basic
oxides.
•1. Reactions with water are:
•CaO + H2O → Ca(OH)2;
•BaO + H2O → Ba(OH)2.
•2. Reactions with acids are:
•SrO + 2HCl → SrCl2 + H2O;
•BaO + 2HNO3 → Ba(NO3)2 + H2O.
•3. Reactions with acidic oxides are:
•CaO + CO2 → CaCO3;
•BaO + SO3 → BaSO4.
•Hydroxides of the alkaline earth metals are strong bases. These react with:
•─ acids
•Ca(OH)2 + 2HCl → CaCl2 + H2O;
•─ acidic oxides
•Sr(OH)2 + CO2 → SrCO3↓;
•─ salts
•Ca(OH)2 + CuCl2 → CaCl2 + Cu(OH)2↓.
•Carbonates of the alkaline earth metals are minerals and are the most important
sources of these elements. Unlike the alkali metal carbonates (other than Li2CO3),
they decompose when heated, giving the oxides and CO2:
15. Beryllium the
Exception
The small size of Be2+ (ionic radius 27 pm) and its consequent high charge
density and polarizing power
The coordination number most commonly observed for this small atom is 4
and the local geometry tetrahedral.
Beryllium’s larger congeners typically have coordination numbers of 6 or
more. Some consequences of these properties are:
A significant covalent contribution to the bonding in compounds such as the
beryllium halides BeCl2, BeBr2, and BeI2 and the hydride, BeH2.
A greater tendency to form complexes, with the formation of molecular
compounds such as Be4O(O2CCH3)6.
Hydrolysis (deprotonation) of beryllium salts in aqueous solution, forming
species suchas [Be(OH2)3OH] and acidic solutions.
Hydrated beryllium salts tend to decompose by hydrolysis reactions, where
beryllium oxo- or hydroxo salts are formed, rather than by the simple loss of
water.
16. Beryllium the Exception
The oxide and other chalcogenides of Be adopt structures with the more directional (4,4)-coordination
structures.
Beryllium forms many stable organometallic compounds, including methylberyllium (Be(CH3)2),
ethylberyllium, t-butylberyllium, and beryllocene ((C5H5)2Be).
Another important general feature of Be is its strong diagonal relationship with Al:
Both Be and Al form covalent hydrides and halides; the analogous compounds of the other Group 2
elements are predominantly ionic.
The oxides of Be and Al are amphoteric whereas the oxides of the rest of the Group 2 elements are basic.
In the presence of excess OH– ions, Be and Al form [Be(OH)4]2– and [Al(OH)4]–, respectively; no
equivalent chemistry is observed for Mg.
Both elements form structures based on linked tetrahedra: Be forms structures built from [BeO4]n and
[BeX4]n tetrahedra (X = halide) and Al forms numerous aluminates and aluminosilicates containing the
[AlO4]n unit.
Both elements form carbides that contain the C4– ion and produce methane on reaction with water; the
other Group 2 carbides contain the C2 2– ion and produce ethyne on reaction with water.
The alkyl compounds of Be and Al are electron-deficient compounds that contain MCM bridges.
There are also analogies between the chemical properties of Be and Zn. For example, Zn
also dissolves in strong bases, to produce zincates, and structures containing linked [ZnO4]n
tetrahedral are common.
Hydrated beryllium salts tend to decompose by hyrodlysis reactions where berrylkium oxo or hydroxox salts are fromed rather than a simple lost of water.
The oxide and other chalcogenides of Be adopt structures with the more directional ( 4,4) – coordination structures. Berryllium forms many stable organometallic compounds including mehylberrylliim and ethyulnberryliium and, t- burhtyberyllium,
