Chapter 11: The Group 1 Elements
• Alkali Metals: lithium, sodium, potassium, rubidium, caesium and francium;
they are all metals and form simple ionic compounds which are soluble in
• The trends in the properties of the Group 1 metals and their compounds can
be explained in terms of variations in their atomic radii and ionization
o Their melting points decrease down the group.
o Ionic and metallic radius increases down the group.
o Ionization energy decreases down the group.
o All the elements adopt a body-centered cubic structure, not close-
o The increase in atomic radius from Li to Cs leads to a decrease in the
first ionization energy down the group because the valence shell is
increasingly distant from the nucleus; this makes reactivity more
reactive as it goes down a group.
o 2 M(s) + 2 H2O(l) 2 MOH(aq) + H2(g)
o Rb Cs react explosively with water because they are denser and sink
below the surface, causing a sudden ignition of the hydrogen that
scatters the water violently.
o The enthalpies of sublimation and ionization both decrease down the
group (making oxidation more favorable).
• The binary compounds of the alkali metals contain the cations of the elements
and exhibit predominantly ionic bonding.
o Most halides have the (6,6)-coordinate rock-salt structure, but CsCl,
CsBr and CsI have the (8,8)-coordinate caesium-chloride structure.
o Li reacts with oxygen to give Li2O.
o Sodium reacts with oxygen to give Na2O2.
o Other Group 1 elements form the superoxides which contain the
paramagnetic ion O2^2-.
o Metals react with sulfur to form compounds with formula M2Sx, where
x lies in the range 1 to 6.
o Only lithium readily forms a nitride Li3N when heated in nitrogen.
o Only lithium reacts with carbon to form Li2C2.
o Group 1 element ions are hard Lewis acids, but their hardness
decreases down the group with increasing ionic radius.
• The chemical properties of Li are anomalous due to its small ionic radius and
tendency to exhibit covalent bonding.
o Lithium can exhibit a high degree of covalent character in its bonding;
this covalent character is due to the high polarizing power of the Li+
ion associated with high charge density.
o Lithium forms the normal oxide when burnt in oxygen whereas other
Group 1 elements form peroxides or superoxides.
o Lithium is the only alkali metal to form a nitride Li3N when heated in
nitrogen and a carbide Li2C2 when heated with graphite.
o Some lithium salts have very low solubilities in water; other lithium
salts crystallize as hydrates or are hygroscopic.
o Lithium forms many stable organometallic compounds.
o Lithium nitrate decomposes directly to the oxide whereas the other
alkali metals initially form nitrites, MNO2.
o Lithium hydride is stable to heating to 900C whereas the other hydrides decompose above 400C.
• The Group 1 elements can be extracted by electrolysis because abundance is
low and should be taken from nature.
• Common uses of lithium are related to its low density and are used when
weight is of a premium concern; the most widely used compounds of Group 1
are NaCl and NaOH.
• The hydrides of Group 1 elements are ionic and contain the H- ion.