Alkali, Alkaline Earth, Aluminum, Halogen, Oxygen, and Sulfur Properties
Element Representation
Alkali and Alkaline Earth Metals
Alkali and alkaline earth metals have low ionization potential (IP) and electron affinity (EA), meaning they easily lose electrons. They have increasing atomic radius (Z) down a column, higher density, and lower melting points.
Physical Properties: Good conductors of heat and electricity, low melting points, and are soft.
Chemical Properties: They are strong reducing agents, readily forming ionic compounds. They react with oxygen to form oxides (e.g., 4Li + O2 = 2Li2O). Group IIA oxides are MO. They react with hydrogen gas to form ionic hydrides (e.g., 2Li + H2 = 2LiH). Hydrides react with water, releasing hydrogen gas (e.g., 2H- + 2H2O = 2OH- + 2H2). They react with acids to form salts (e.g., 2K + 2HCl = 2KCl + H2). They react with water (e.g., 2Na(s) + 2H2O(l) = 2Na+ + 2OH- + H2).
Obtaining: They have high oxidation states, forming ionic salts. Pure metals are difficult to obtain by chemical methods, requiring electrolysis of molten salts.
Uses: Magnesium is used in lightweight alloys, often with aluminum, for light objects.
Aluminum (IIIA)
Aluminum is the third element in Group IIIA and is a metal. It is found in ores, the most important being bauxite (Al2O3·2H2O). It is obtained by electrolysis of bauxite.
Properties: It has a +3 oxidation state. Most of its salts are soluble in water. It dissolves in acids and bases. When Al3+ salts are treated with OH-, NH4OH, CO32-, etc., a gelatinous precipitate forms, typically represented as Al2O3·H2O, but more accurately as Al(OH)3. It is amphoteric.
- Al3+(aq) + 3OH-(aq) = Al(OH)3(s)
- Al(OH)3(s) + OH- = [Al(OH)4]-(aq)
- [Al(OH)4]- + H+ = Al(OH)3(s) + H2O
- Al(OH)3(s) + H+ = Al3+ + 3H2O
Halogens (VIIA)
Halogens have an ns2np5 electron configuration, high ionization potential, high electron affinity, and high electronegativity. They form strong networks.
Physical Properties: F2 (gas), Cl2 (gas), Br2 (liquid), I2 (solid).
Obtaining: They are obtained by electrolysis of their molten salts. F2 and Cl2 are obtained this way. Br2 is obtained from seawater by oxidizing Br-(aq) with Cl2(g) (e.g., Cl2(g) + 2Br-(aq) = Br2(l) + 2Cl-(aq)). I2 is obtained as a byproduct of natural nitrate production.
Chemical Properties: They have great variety, forming ionic compounds with metals and covalent compounds with nonmetals.
Family (VIA) Oxygen
Oxygen has high electronegativity, similar to chlorine. It forms ionic compounds with metals and covalent compounds with nonmetals. Its electron configuration is ns2 2s2 2p4, with two unpaired electrons in the 2p orbitals, making it paramagnetic. Its molecular structure is described by molecular orbitals.
Ozone (O3)
Ozone is a resonant structure. It forms in the air:
- O2(g) + hf = O(g) + O(g)
- O2(g) + O(g) = O3(g)
Ozone decomposes with UV light:
- O3(g) + hf = O2(g) + O(g)
- O3(g) + O(g) = 2O2(g)
Ozone is a powerful oxidizing agent:
- O3(g) + 2H+(aq) + 2e- = O2(g) + H2O
Hydrogen Peroxide (H2O2)
H2O2 is an important oxygen compound. It is both an oxidizing and reducing agent:
- Oxidation: H2O2 + 2I- + 2H+ = 2H2O + I2
- Reduction: Cl2 + H2O2 = O2 + 2H+ + 2Cl-
It is obtained by electrolysis.
Uses: Antiseptic, whitening cellulose. It decomposes easily: H2O2 = H2O + O2.
Most elements form compounds, except for noble gases. Oxides are the most common. They are difficult to classify: ionic (normal, peroxides, superoxides), acidic, amphoteric. Oxoacids are generated when dissolved in water (e.g., SO3 + H2O = H2SO4). Basic oxides react with water or certain bases (e.g., Na2O + H2O = 2NaOH). Amphoteric oxides react with both acids and bases (e.g., Al2O3 + 6HCl = AlCl3 + 3H2O; Al2O3 + 2NaOH + 3H2O = 2Na[Al(OH)4]).
Sulfur
Sulfur has several molecular forms (allotropy). It has properties similar to oxygen, forming ionic compounds with metals (e.g., CuS, Na2S) and covalent compounds with nonmetals (e.g., SO2, SC2).
Oxides: S2O, S2O3, S2O7, SO2, SO3, SO4.
Roasting of copper sulfide mineral:
- CuS + 3O2 = 2CuO + 2SO2
- S(s) + O2 = SO2(g)
SO3 is produced by oxidation of SO2.
Oxyacids of Sulfur: H2SO3 (sulfurous acid), H2SO4 (sulfuric acid). Thiocompounds are formed when an oxygen is replaced by a sulfur (e.g., SO4(2-) => S2O3(1-)).
Solubility of Sulfides: Soluble in H2O (K2S, Na2S, CaS), in HCl (MnS, FeS, CoS, ZnS), in HNO3 (CdS, PbS, CuS), in KOH (SnS, As2S3, Sb2S3), and insoluble in pure water (HgS).