Chemistry

4813 s and p – Block ElementsThe Structure of Carbon DioxideThe dipole moment of carbon dioxide is zero. Therefore it is a linear molecule.The Structure of Silicon DioxideIt is a macromolecular compound, in which silicon and oxygen atoms are linked togethercovalently in tetrahedral basic unit. In crystobalite, these units are joined as in diamond, while inquartz and tridymite they are arranged spirally around an axis. Because of its structure silicondioxide is non-volatile and hard unlike carbon dioxide. Triatomic molecules of silicon dioxideand carbon dioxide, carbon and silicon are similar in having.(i) 4 valence electrons.(ii) 4 covalent bond formation.But they show a lot of difference in their physical properties. It is due to the fact that:(i)Silicon atoms are much larger in size than carbon atoms and thus tend to be surroundedby more oxygen atoms.Fig 13.37: Silicon dioxide(ii)Silicon from only single born with oxygen atomswhile carbon forms double bonds.(iii) Carbon forms a linear molecule of CO2 with twooxygen atoms while silicon atom is bound to fouroxygen atoms in a tetrahedral structure whichresult in the formation of silicon dioxide crystalThe simplest formula for silica is SiO2. Howeverthe whole crystal of silicon can be considered asone molecule.The Acid-Base Behaviour of the Group 4 OxidesThe oxides of the elements at the top of Group 4 are acidic, but acidity of the oxides fallsas you go down the Group. Towards the bottom of the Group, the oxides become more basic -although without ever losing their acidic character completely.An oxide which can show both acidic and basic properties is said to be amphoteric.The trend is therefore from acidic oxides at the top of the Group towards amphoteric onesat the bottom.Carbon and Silicon OxidesCarbon MonoxideCarbon monoxide is usually treated as if it was a neutral oxide, but in fact it is very, veryslightly acidic. It doesn't react with water, but it will react with hot concentrated sodium hydroxidesolution to give a solution of sodium methanoate.The fact that the carbon monoxide reacts with the basic hydroxide ion shows that it mustbe acidic.