Читать книгу Foundations of Chemistry - Philippa B. Cranwell - Страница 109

Sulfur, the central atom, is in Group 6 (Group 16), so it has six valence electrons and needs to gain two more to complete the octet. This is achieved by bonding to hydrogen. There are four areas of electron density around sulfur consisting of two single bonds and two lone pairs of electrons. The four areas of electron density arrange themselves as far apart as possible and form a tetrahedral shape. However, because two of these areas of electron density are lone pairs, the actual shape of the molecule appears to be bent (i.e. we can't ‘see’ the lone pairs!). As discussed previously, lone pairs of electrons occupy more space than bonding pairs of electrons, and push the hydrogen atoms more closely together. The H—S—H bond angle is therefore slightly less than 109.5°. So although the arrangement of electron centres is based on a tetrahedron, it is slightly distorted, and hydrogen sulfide is therefore bent (also called v‐shaped or angular).