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Describe the trend in the PHYSICAL and CHEMICAL properties of the CHLORIDES and OXIDES in period 3 of the periodic table (i.e. Na - Ar). Illustrate your essay with specific examples.


The chlorides and oxides of period 3 elements of the periodic table have been extensively studied and investigated and include many interesting and industrially important compounds. These compounds exhibit distinctive properties which vary widely across period 3, ranging from the use of sodium chloride in the chlor-alkali industry to produce chlorine and caustic soda (described by Cheresource, 2004); the use of inert silicon dioxide as a filler in building materials (see for example, Dorfner, no date (n.d.)), glass and in the electronics industry; phosphorus pentoxide (P4O10) which takes advantage of its strong affinity for water to be an excellent drying agent (Cotton FA, 1999); and the volatile gaseous oxides of sulphur used in the contact process for the production of sulphuric acid (as described by Encarta, 2007). The following sections will outline how these broad ranging physical and chemical properties can be explained in terms of the chemical bonding and structure of the oxides and chlorides, and the way in which the trends manifest themselves from left to right across group 3 of the periodic table.

Trends in the PHYSICAL properties of the OXIDES

The group 3 elements (sodium to chlorine) form a number of oxides of varying oxidation states as illustrated in table 1 below. Note that the noble gas argon does not form stable isolatable oxides due to its electron configuration with a full octet of outer shell electrons.

Finally, silicon tetrachloride and phosphorus pentachloride both react violently with water, generating fumes of hydrogen chloride:


The variation in the physical and chemical properties of the chlorides and oxides of the elements across period three can be explained by general trends in the bonding and structure of the compounds. The elements towards the left hand side of the period form large, stable ionic structures with high melting and boiling points and compounds which exhibit strongly basic chemical characteristics. Moving across the period, the bonding becomes increasingly covalent, with the compounds on the right hand side forming simple molecular structures with low boiling points, and increasing acidic nature. However, there are certain anomalies in these trends in physical and chemical properties, which can be explained by detailed consideration of the individual structures.

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