Oxygen the Ubiquitous Element - Coursework Example

Oxygen the Ubiquitous Element Introduction Oxygen is the most important element for living beings because this is essential for life. This gas literally supports the life. This gas was discovered by Carl Scheele, Joseph Pristely and Antoine Lavoisier [1]. Carl Scheele had independently discovered oxygen in 1973 and named it “fire gas” [2]. However, his work was published in 1977 and by then Joseph Pristely and Antoine Lavoisier working in collaborative mode had already discovered this gas. Pristely and Lavoisier had made this gas first by heating mercury oxide (HgO) and subsequently by heating many other oxides. In fact Antoine Lavoisier used these reactions to establish conservation of matter during chemical reactions. Oxygen is the second most abundant element in atmosphere after nitrogen. It is approximately 21% by volume. It is a colorless and odorless gas at room temperature. Some of its important physical properties are listed below [3] in Table 1. Table 1: Some Important Physical Properties of Oxygen [3] Atomic Number 8 Ionization Enthalpy (kJ/mol) 1314 Atomic Mass (g/mol) 16 Electronegativity 3.5 Electronic Configuration 1s22s22p4 Density 298 K (g/cm-3) 1.32 Covalent Radius (pm) 66 Melting Point (K) 55 Ionic radius E2 (pm) 140 Boiling Point (K) 90 Electron Gain Enthalpy (kJ/mol) -141 Oxidation States -2, -1, 0, 1, 2 Its symbol is O and as pure element it occurs in nature as diatomic molecule O2 and triatomic molecule O3 or ozone (in upper crust of the atmosphere). Its atomic number is 8. It has three stable isotopes namely 16O, 17O and 18O. Besides, it has ten radioactive isotopes – 12O, 13O, 14O, 15O, 19O, 20O, 21O, 22O, 23O and 24O [4]. It has 8 protons in its nucleus and therefore 8 electrons in different orbits around its nucleus. Therefore its electronic configuration is 1s22s22p4. In box notation the electronic configuration will be the following. 1s 2s 3px 3py 3pz It can be seen that oxygen needs two electrons to complete its octate and hence to attain stable electronic configuration. This is the reason why it is highly electronegative. It is the second most electronegative element only next to fluorine and hence always remains in negative oxidation states except in its pure forms O2 and O3 (oxidation number is zero), in OF2 (oxidation number is +2) and in O2F2 (oxidation number is +1). It is bivalent because it needs two electrons to complete its octate. It is highly reactive and forms readily oxides with most of the elements barring noble metals like Au (gold), Pt (Platinum) etc. and inert gases. The reaction with oxygen is an exothermic process and therefore self sustaining; however, to initiate the reaction some initial heating is required to dissociate the double bond in O2. Compounds of Oxygen Oxygen forms numerous compounds due to its high reactivity. This section presents briefly describes synthesis, structure and properties of ten important compounds of oxygen. (1) Water: Its formula is H2O and its structure is the following. Its shape is angular due to presence of two lone pair of electrons on the central atom (Oxygen). This compound is liquid at room temperature. Its freezing point is 0 oC and boiling point is 100 oC. This is found in abundance on the planet Earth, mostly in the form of liquid. However, all the three forms – solid, liquid and vapor of this compound is found on this planet. It can be synthesized by crating a spark in a mixture of oxygen and hydrogen. (2) Hydrogen Peroxide: Its formula is H2O2. It is a non-planar molecule. Its structure in gas phase is shown below. It is prepared by reaction of Barium oxide with H2SO4. The excess water in this reaction is removed by evaporation at reduced pressure. It is a pale blue (almost colorless) liquid at room temperature. Its freezing point is 272.4 K and boiling point is 423 K. It is miscible in water in all proportions. (3) Carbon Dioxide: Its formula is CO2. It is a linear molecule. Its structure is shown below. It is prepared by complete combustion of fossil fuels in excess oxygen. It is also prepared by thermal decomposition of lime stone. It is a colorless gas at room temperature. (4) Dinitrogen Oxide: Its formula is N2O. Its structure is given below. It is a linear molecule due to absence of lone pair of electrons on the central atom (N). This is a colorless and neutral gas. This is prepared by heating ammonium nitrate. (5) Nitrogen Monoxide: its formula is NO. It is a linear molecule. Its structure is shown below. It is a colorless and neutral gas. It is prepared by reaction between sodium nitrite with ferrous sulfate in sulfuric acid. (6) Dinitrogen Trioxide: Its formula is N2O3. It is an angular molecule. Its structure is given below. It is a blue colored solid and is acidic in nature. It is prepared by reaction between nitrogen monoxide and dinitrogen tetroxide. (7) Nitrogen Dioxide: Its formula is NO2. It is an planar molecule. Its structure is shown below. It is a brown acidic gas and is prepared by heating of lead nitrate at 400 oC. (8) Dinitrogen Tetroxide: Its formula is N2O4. It is a planar molecule. Its structure is shown below. It is essentially a dimer of nitrogen dioxide and is prepared by dimerization of nitrogen dioxide in appropriate temperature and pressure condition. It is a colorless solid / liquid and is acidic in nature. (9) Dinitrogen Pentoxide: Its formula is N2O5. It is a planar molecule. Its structure is shown below. It is a colorless solid and acidic in nature. It is prepared by chemical reaction between Nitric Acid and Tetra Phosphorous Decoxide. (10) Sulphur Dioxide: Its formula is SO2. It is an angular molecule. Its structure is shown below. It is a colorless gas with pungent smell. It is soluble in water and is highly acidic in nature. It is prepared by roasting of sulfide ores like pyrites or burning of S in air. Uses of Oxygen The first and foremost use of oxygen in our everyday life every moment of life is breathing. Without breathing in this gas we cannot afford to survive beyond a couple of minutes. Oxygen cylinders are used for evacuation purpose in case of fire and other accidents. It is used by deep sea divers and astronauts for the same purpose. This is used in combustion of acetylene for oxy-acetylene welding. It is use for combustion of fuels like hydrazine for rocket propulsion. It is used for making of steel from hot metal from blast furnace by removing carbon from the same. Uses of Five Compounds of Oxygen (1) Water: Whatever is written about use of water will remain too short. It acted as a cradle for birth of life on this planet and continues to act as savior of the same. It is used for drinking as it is the medium in which all the metabolic reactions take place. It is used for cooking food, for taking bath, washing clothes, dissolving different reagents for making the medium of different chemical reactions. (2) Hydrogen Peroxide: It is used as an antiseptic. Besides, it is used as hair beach and also as bleaching agent in textile, paper and pulp and leather industries. It is used for making certain food products and certain pharmaceutical products. It is also used for treatment of domestic and industrial effluents. (3) Heavy Water: It is used as moderator and / or coolant in nuclear reactors. As a moderator, heavy water slows down or thermalizes the fast neutrons produced in fission of heavy nuclides like 235U and 239Pu. As coolant, it collects the heat produced in the core of a nuclear reactor and brings it to the steam generator, where its heat is extracted by another loop. (4) Carbon Dioxide: It is used in soft drinks. It is used as fire extinguisher. It is used by plants for photosynthesis; which is the most important mechanism for capturing the solar energy for consumption by all the living beings. Dry ice or solid carbon dioxide is used as refrigerant. It is also used as active gas in arc welding of steels and in manufacturing of urea. (5) Sulfur Dioxide: It is used for purification of sugar and petroleum. It is used as disinfectant and preservative. It is also used as bleaching agent for wool and silk.It is used for making sulfuric acid which is an important chemical reagent. It is also used as solvent for many chemical reagents. Conclusions: It can be concluded that oxygen is very useful element and it forms many useful compounds by combining with different elements. References [1] Kuhn T. S.” Historical Structure of Scientific Discovery” Retrieved on March 22, 2010 from http://www.sciencemag.org/cgi/reprint/sci%3B136/3518/760.pdf [2] “A Brief History of the Study of Gas Chemistry” Retrieved on March 22, 2010 from http://mattson.creighton.edu/GasWebDocuments/History_Gas_Chemistry.pdf [3] “The p-Block Elements”, Chapter 7, Class XII, Chemistry Part – I, page 182. Retrieved from http://www.ncert.nic.in/textbooks/testing/Index.htm on March 22, 2010 [4] “Isotopes of Oxygen (Z=8)”, Retrieved from http://ie.lbl.gov/education/parent/O_iso.htm on March 22, 2010 Read More