Chapter 12: The Group 2 Elements
• Alkaline Earth Metals: calcium, strontium, barium and radium, but applied to
all of Group 2.
• The most important factors influencing the chemical properties of the Group 2
elements are their ionization energies and ionic radii.
o Group 2 elements have a greater mechanical hardness and higher
melting points because of an increase in the strength of metallic
bonding from Group 1 to 2.
o The ionization energies of the elements decrease down the group as
the radius increases and the elements become more reactive and
more electropositive as it becomes easier to form the +2 ions.
o M(s) + 2 H2O(l) M(OH)2(aq) + H2(g)
o All elements occur as hexagonal close-packed structures with the
exception of Ba and Ra, which adopt the more open body-centered
o The density decreases from Be to Mg to Ca due to strong metallic
• The binary compounds of the Group 2 metals contain the cations of the
elements and exhibit predominantly ionic bonding.
o Except Be, the Group 2 elements form ionic hydrides; the anion
present is the hydride ion, H-.
o Beryllium hydride adopts a 3-D network of linked Beh4 tetrahedra.
o The fluorides of the larger cations (Ca to Ba) adopt the (8,4)-coordinate
fluorite structure but MgF2 crystallizes with a rutile structure.
o Beryllium oxide, BeO, has a wurtzite structure with (4,4)-coordination
and the oxides of the other Group 2 elements all adopt the rock-salt
structure with (6,6)-coordination.
o BaO(s) + H2O(l) Ba2+(aq) + OH-(aq); same as SrO.
o Be(OH)2(s) + 2 OH-(aq) Be(OH)4^2-(aq)
o The elements Mg-Ra react directly with nitrogen when heated to
produce the nitrides M2N3, which react with water to produce
o In general, the salts of the Group 2 elements are generally much less
soluble in water than those of Group 1 on account of the higher lattice
enthalpies of structures containing doubly charged cations.
• The small size of Be2+ and its consequent high charge density and polarizing
power results in the compounds of Be being largely covalent; the ion is a
strong Lewis acid.
• Beryllium typically has a coordination number of 6 or more.
o A significant covalent contribution to the bonding in compounds such
as beryllium halides BeCl2, BeBr2 and BeI2 and the hydride, BeH2.
o A greater tendency to form complexes, with the formation of molecular
compounds such as Be4O(O2CCH3)6.
o Hydrolysis of beryllium salts in aqueous solution, forming species such
as [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.
o The oxide and other chalcogenides of Be adopt structures with the
more directional (4,4)-coordination strucutres.
o Beryllium forms many stable organometallic compounds like
(Be(CH3)2) and ((C5H5)2Be). • Be has a strong diagonal relationship with Al.
o Both Be and Al form covalent hydrides and halides; the analogous
compounds of the other Group 2 elements are predominantly ionic.
o The oxides of Be and Al are amphoteric whereas the oxides of the rest
of the Group 2 elements are basic.
o In the presence of excess OH- ions, Be and Al form [Be(OH)4]^2- and
[Al(OH)4]^2-; no equivalent chemistry is observed for Mg.
o Both elements form structures based on linked tetrahedral: Be forms
structures built from [BeO4]^n- and [BeX4]^n- tetrahedral (X = halide)
and Al forms numerous aluminates and aluminosilicates containing the
o Both elements form carbides that contain the C^4- 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.
o The alkyl compounds of Be and Al are electron-deficient compounds
that contain M-C-M bridges.
• Magnesium is the only Group 2 element extracted on an industrial scale;
magnesium, calcium, strontium and barium can be extracted from molten
o CaO(s) + H2O(l) Ca2+(aq) + 2OH-(aq)
o Mg2+(aq) + 2 OH-(aq) Mg(OH)2(s)
o Mg(OH)2(s) + 2HCl(aq) MgCl2(aq) + 2 H2O(l)
• Magnesium and its compounds have major applications in pyrotechnics, alloys
and common medicines; calcium compounds are widely used in the
construction industry; magnesium and calcium are very important for
o Beryllium is unreactive in air so it is resistant to corrosion; it is also one
of the lightest metals so people use in alloys to make precision
instruments and missiles.
o Magnesium metal burns in air with an intense white flame so it is used
o Calcium oxide is a major component of mortar and cement.
• All the Group 2 elements form saline hydrides with the exception of beryllium,
which forms a polymeric covalent compounds.
o MgH2(s) + 2 H2O(l) Mg(OH)2(s) + 2 H2(g)
o Mg(s) + H2(g) MgH2(s)
• The halides of beryllium are covalent; all the fluorides, except BeF2 are