Dichlorine, dibromine and diiodine

   Dichlorine is a pale green-yellow gas with a characteristic odour. Inhalation causes irritation of the respiratory system and liquid Cl₂ burns the skin. Reaction 1.1 can be used for small-scale synthesis, but, like F₂, Cl₂ may be purchased in cylinders for laboratory use.

       (1.1)

   Dibromine is a dark orange, volatile liquid (the only liquid non-metal at 298 K) but is often used as the aqueous solution ‘bromine water’. Skin contact with liquid Br₂ results in burns, and Br₂ vapour has an unpleasant smell and causes eye and respiratory irritation. At 298 K, I₂ forms dark purple crystals which sublime readily at 1 bar pressure into a purple vapour.   In the crystalline state, Cl₂, Br₂ or I₂ molecules are arranged in layers as represented in Figure 1.1. The molecules Cl₂ and Br₂ have intramolecular distances which are the same as in the vapour (compare these distances with r_cov, Table 16.1). Intermolecular distances for Cl₂ and Br₂ are also listed in Figure 1.1; the distances within a layer are shorter than 2r_v (Table 16.1), suggesting some degree of interaction between the X₂ molecules. The shortest intermolecular X…..X distance between layers is significantly longer. In solid I₂, the intramolecular I^_I bond distance is longer than in a gaseous molecule, and the lowering of the bond order (i.e. decrease in intramolecular bonding) is offset by a degree of intermolecular bonding within each layer (Figure 1.1).

Fig. 1.1 Part of the solid state structures of Cl₂, Br₂ and I₂ in which molecules are arranged in stacked layers, and relevant intramolecular and intermolecular distance data.

   The molecules Cl₂ and Br₂ have intramolecular distances which are the same as in the vapour (compare these distances with r_cov, Table 16.1). Intermolecular distances for Cl₂ and Br₂ are also listed in Figure 1.1; the distances within a layer are shorter than 2r_v  suggesting some degree of interaction between the X₂ molecules. The shortest intermolecular X…..X distance between layers is significantly longer. In solid I₂, the intramolecular I_I bond distance is longer than in a gaseous molecule, and the lowering of the bond order (i.e. decrease in intramolecular bonding) is offset by a degree of intermolecular bonding within each layer (Figure 1.1). It is significant that solid I₂ possesses a metallic lustre and exhibits appreciable electrical conductivity at higher temperatures; under very high pressure I₂ becomes a metallic conductor. 

     Chemical reactivity decreases steadily fromCl₂ to I₂, notably in reactions of the halogens with H₂, P₄, S₈ and most metals. The values of Eo inTable 16.1 indicate the decrease in oxidizing power along the series Cl₂ > Br₂ > I₂, and this trend is the basis of the methods of extraction of Br₂ and I₂ described in Section 16.2. Notable features of the chemistry of iodine which single it outamong the halogens are that it ismore easily:

• oxidized to high oxidation states;
• converted to stable salts containing I in the 1 oxidation state (e.g. Figure 16.4).

مواضيع ذات صلة

تطبيق ثلاثيات العدد الذري على المجموعة ٣

تطبيق نفس المعيار على عناصر أخرى يصعب تسكينها في أماكن مناسبة

معيار جديد: الحفاظ على الثلاثيات أو ابتكار ثلاثيات جديدة

بعض الحالات الخاصة

أنماط الجدول الدوري

كيميائية العناصر التخليقية

العناصر من ١١٣ إلى ١١٨

العنصر ١٠٧ وما بعده

العناصر من ١٠١ إلى ١٠٦

عناصر ما بعد اليورانيوم الحقيقية

العناصر الناقصة

الخيمياء الحديثة: من عناصر ناقصة إلى عناصر تخليقية