46 | The History and Use of Our Earth’s Chemical Elements various grades of purity. A relatively low grade of sulfuric acid is used in the manufacture of
46 | The History and Use of Our Earth’s Chemical Elements various grades of purity. A relatively low grade of sulfuric acid is used in the manufacture of
fertilizers. Sulfurous acid (H 2 SO 3 ) can be produced by burning sulfur to form sulfur dioxide (SO 2 ) gas and by then dissolving the gas in water to form sulfurous acid. This is the acid produced by burning coal that has a high sulfur content; the gaseous sulfur dioxide by-product of combus- tion then combines with atmospheric water to form “acid rain.”
Hydrides Hydrides are inorganic compounds in which at least one of the elements is hydrogen;
therefore, there are thousands of carbon-hydrogen hydride compounds. One of the main building blocks of hydrocarbon chemistry is methane (CH 4 ), which is ordinary natural gas, sometimes called “swamp gas” because it is one of the by-products of decaying organic matter. The bonding of hydrides can be either ionic or covalent, and the molecules may be binary or complex. Common metallic forms are hydrides of lithium (LiH), sodium (NaH), potassium
(KH), and aluminum (AlH 3 ). Hydrides react violently in both air and water as well as with some nonmetals, resulting in an explosion of hydrogen gas.
IsotopesofHydrogen There are three isotopes of the element hydrogen; the first and most common isotope has
just one proton in its nucleus ( 1 H). This isotope is also called protium. The second isotope contains one proton and one neutron and is called deuterium ( 2 D). The third has an atomic mass of three and is called tritium ( 3 T) and is very rare. In water, only one tritium atom exists for every 10 18 atoms of normal hydrogen. The oxide of deuterium (D 2 O or DOD) molecule is almost twice as heavy as a regular water molecule and thus is referred to as deuterium oxide or “heavy water.” There is only about one molecule of deuterium (D 2 O) for every 6,500 mol- ecules of regular H 2 O. Deuterium is used as heavy water for a moderator in nuclear accelera- tors. There are several processes used to produce and collect heavy water. One is fractional distillation; another is by electrolysis, during which about 100,000 gallons of regular water is required to produce just one gallon of pure heavy water.
HydrocarbonsandOrganicCompounds We have already discussed the role of carbon in these types of molecules. Hydrogen also
plays a major role in the formation of both organic foods and hydrocarbons. Hazards
Hydrogen gas is very explosive when mixed with oxygen gas and touched off by a spark or flame. On May 6, 1937, the German rigid-frame dirigible or zeppelin, Hindenburg, which was inflated with hydrogen, exploded while landing at Lakehurst, New Jersey. The explosion killed thirty-six people and injured many more when the dirigible attempted to land during
a thunder and lightning storm. Many hydrides of hydrogen are dangerous and can become explosive if not stored and handled correctly. Many organic and hydrocarbon compounds are essential for life to exist, but just as many are poisonous, carcinogenic, or toxic to living organisms.
Guide to the Elements | 47 LITHIUM
SYMBOL:Li PERIOD:2 GROUP:1(IA) ATOMICNO:3 ATOMICMASS:6.941amu VALENCE:1 OXIDATIONSTATE:+1 NATURALSTATE:
Solid ORIGINOFNAME:ThenamelithiumcomesfromtheGreekwordlithos,meaning“stone” becauseitwasfoundinrocksonEarth. ISOTOPES:Therearetwostablelithiumisotopes:Li-6.015,whichmakesup7.5%ofalllith- iumatoms,andLi-7.016,whichmakesup92.5%oflithiumatomsfoundintheEarth’s crust.LessprevalentisotopesoflithiumareLi-4,Li-5,Li-8,Li-9,Li-10,andLi-11.They areunstablewithshorthalf-livesandmakeuponlyaverysmallfractionofLithium’s totalaveragedatomicweight.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
Properties In the metallic state, lithium is a very soft metal with a density of 0.534 g/cm 3 . When a
small piece is placed on water, it will float as it reacts with the water, releasing hydrogen gas. Lithium’s melting point is 179°C, and it has about the same heat capacity as water, with a boiling point of 1,342°C. It is electropositive with an oxidation state of +1, and it is an excel- lent conductor of heat and electricity. Its atom is the smallest of the alkali earth metals and thus is the least reactive because its valence electron is in the K shell, which is held closest to its nuclei.
Characteristics While classified as an alkali metal, lithium also exhibits some properties of the alkali earth
metals found in group 2 (IIA). Lithium is the lightest in weight and softest of all the metals and is the third lightest of all substances listed on the periodic table, with an average atomic weight of about 7. (The other two are hydrogen and helium.) Although it will float on water,
it reacts with water, liberating explosive hydrogen gas and lithium hydroxide (2Li + 2H 2 O→ 2LiOH + H 2 ∆). It will also ignite when exposed to oxygen in moist air (4Li + O 2 → 2Li 2 O). It is electropositive and thus an excellent reducing agent because it readily gives up electrons in chemical reactions. Lithium is the only metal that reacts with nitrogen at room temperature. When a small piece of the metal, which is usually stored in oil or kerosene, is cut, the new surface has a bright, shiny, silvery surface that soon turns gray from oxidation.