History and Production
The word lead is Anglo-Saxon while in Latin it is called plumbum. Long known since prehistoric times. It was used in ancient Egypt for glazing pottery since at least 5000 BC. The Romans used lead for water pipes and plumbing. The metal is obtained by roasting galena (PbS) in air to give PgO which is then reduced with coke in a blast furnace. It is further purified by electrolytic refinement method. This yield lead (at cathode) with purity grade of 99.99%. Zone-refining method can be used to obtain a much purer form of the metal.
The metal is mainly used as alloys such as in storage batteries (91% Pb, 9% Sb). With tin in making organ pipes, solders and bearing metals. It is also used in ammunition and weights. Lead is also used as a radiation shield for X-ray equipment and nuclear reactors. It is also used to make rusting-inhibiting paints such as read lead oxide (Pb3O4) and yellow chromate (PbCrO4). Recently, the use of the lead compound (tetraethyl) as an 'anti-knock'
agent in gasoline is diminishing especially in countries with strict environmental lagislation.
It is a bluish-grey metal of bright luster, soft, ductile and very malleable. It is a poor conductor of electricity but very resistant to corrosion. The metal has a natural abundance of about 13 ppm. It is rarely distributed as native but is usually found in minerals such as galena (left), anglesite (PbSO4) and cerussite (PbCO3) etc.
Interatomic distance: 350.0 pm
Melting point: 327.46°C
Boiling point: 1749°C
Thermal conductivity/Wm-1K-1: 35.3 (27°C)
Density/kgm-3: 11350 (20°C), 10678 (m.p.)
Standard Thermodynamic Data (atomic gas)
Enthalpy of formation: 195.2 kJ/mol
Gibbs free energy of formation: 162.2 kJ/mol
Entropy: 175.4 J/mol K
Heat capacity: 20.8 J/mol K
Electronic configuration: [Xe] 4f14 5d10 6s2 6p2
Term symbol: 3P0
Electron affinity: 35.1207 kJ/mol Electronegativity (Pauline): 1.80
Ionization energy (first, second, third): 715.599, 1450.39, 3081.48 kJ/mol
Lead is slightly attacked in soft water to give lead(II) hydroxide, Pb(OH)2. But in hard water, the presence of small amount of carbonate and sulfate ions causes a reaction with the hydroxide to give a protective layer, which
stops further attack. Lead is not readily attacked by hydrochloric or sulfuric acids. However, hot concentrated sulfuric acid reacts slowly with the formation of lead(II) sulfate, PbSO4. Nitirc acid reacts with lead to give lead(II) nitrate, Pb(NO3)2 and oxides of nitrogen.
Finely divided lead can form oxides when heated in air. With limited supply of air, lead(II) oxide or litharge is formed. With ample amount of air, red lead, Pb3O4, is formed. Finely divided lead will also dissolve in solutions of sodium in liquid ammonia, giving Na4Pb9, which is green in solution.
Test for lead(II) ions:
(1) Hydrochloric acid gives a white precipitate of chloride.
(2) Potassium chromate gives a yellow precipitate of chromate.
(3) Potassium iodide gives a yellow precipiate of lead(II) iodide which dissolves on heating. On cooling, the iodide reappears in the form of characteristic glistening 'spangles'.