Chlorides, of Period 3 elements

Lesson 1 - Chlorides of Period 3 elements. -Students were required to construct relevant concept maps during the lesson using the pre-struclured formats given in Figs. 14 and L5. 

Fig. 14 Pre-structured format used by students to construct concept maps in Cycle 3 on the chlorides of Period 3 elements...

Table 10.12 The structure and bonding of the chlorides of Period 3 elements and the effect of water on these chlorides.

Across a period, the chlorides of Period 3 elements change from ionic compounds that dissolve in water to covalent compounds that are hydrolysed by water, releasing fumes of hydrogen chloride and leaving an acidic solution. 

The fact that the elements become less metallic, from left to right across a period, is shown by the characters of their chlorides and oxides. The chlorides of metals on the left-hand side of a period are ionic and dissolve in water to form neutral solutions whereas the chlorides of non-metals on the right-hand side of the table are covalent and react with water. There is a gradual change between these two extremes across the period. Consider the chlorides of period 3 ... 

As with the oxides of Period 3 elements, the chlorides also show characteristic behaviour when we add them to water. Once again, this is linked to their structure and bonding (Table 10.12). 

In this section we discuss the bonding of the fluorides, chlorides, and hydrides of the elements of periods 3 and beyond with LLP coordination numbers up to four with particular emphasis on the elements of period 3. As might be expected these molecules show many similarities to the corresponding period 2 molecules, and the differences can be mainly attributed to the larger size and lower electronegativity of the atoms of a period 3 element compared to the corresponding period 2 element. 

Figure 9.23 Properties of the Period 3 chlorides. Samples of the compounds formed from each of the Period 3 elements with chlorine are shown in periodic table sequence in the photo. Note the trend in properties displayed in the bar graphs as AEN decreases, both melting point and electrical conductivity (at the melting point) decrease. These trends are consistent with a change in bond type from ionic through polar covalent to nonpolar covalent.

We will now look at the chemistry of some of the elements of Period 3 and their compounds, focusing on the oxides and chlorides. 

Oxidation numbers of the Period 3 elements in their chlorides... 

Table 10.11 shows the formulae of the common chlorides of the Period 3 elements. 

Table 10.11 Oxidation numbers of the Period 3 elements in their chlorides. Phosphorus also has a chloride with the formula PCI3, in which its oxidation number is +3. Sulfur also has a chloride SjClj, in which its oxidation number is +1.

Trithioles and 1,3,2-dioxathiolanes. 1,2,3-Trithiolanes are prepared by reaction of alkenes with elemental sulfur . The synthesis of 1,3,2-dioxathiolane -oxides (cyclic sulfites) and 1,3,2-dioxathiolane S, -dioxides (cyclic sulfates) is discussed in comprehensive reviews <1997AHC(68)89, 2000T7051>. The most widely used method for the preparation of 1,3,2-dioxathiolane A-oxides 557 is the reaction of the corresponding 1,2-diols 556 with thionyl chloride in the presence of pyridine or triethylamine (Scheme 251). More reactive 1,3,2-dioxathiolane S,A-dioxides 558 are usually obtained by oxidation of sulfites 557 with sodium periodate, which is mediated by ruthenium tetroxide generated in situ from a catalytic amount of ruthenium trichloride <1997AHC89, 2000T7051, CHEC-III(6.05.10.3)183>. 

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