It is only slightly soluble in water and so the solution is only slightly alkaline (pH = 9). It dissolves in water to give an alkaline solution (pH = 14). They can thus behave as either acids or bases and are thus AMPHOTERIC. Intermediate oxides can react in either of the above ways, depending on the conditions. This attracts the lone pair on water molecules, releasing H ions: This is a strongly basic ion which reacts with water to produce hydroxide ions:Ĭovalent oxides do not contain ions, but have a strongly positive dipole on the atom which is not oxygen. P 4O 10 is a much bigger molecule than SO 3 and so has a much higher melting point, as the van der Waal’s forces are stronger.Īcid-base character of oxides P 4O 10 and SO 3 are molecular covalent and so only intermolecular forces (Van Der Waals) exist between the molecules. There are strong covalent bonds between all the atoms and thus lots of energy is required to break them. SiO 2 has a giant covalent structure and hence a high melting point. MgO and Al 2O 3 have a higher melting point than Na 2O since the charges are higher and the atomic radii smaller, resulting in a stronger electrostatic attraction (forces) between the ions. Na 2O, Al 2O 3 and MgO are ionic oxides and hence have a high melting point. The physical properties of these oxides depend on the type of bonding. Sulphur melts easily and burns with a blue flame forming sulphur(IV) oxide (sulphur dioxide), a colourless gas with a choking odour.Īnother oxide, SO 3 is formed in a reversible process when SO 2 and O 2 are heated with a V 2O 5 catalyst (the Contact Process). This is a vigorous reaction forming masses of white fumes of phosphorus(V) oxide. The oxidation number of P in this oxide is +5. This reaction is vigorous with a brilliant white flame forming a white ash of magnesium oxide.Īl 2O 3 is mostly ionic, but there is significant covalent character. Na can also react with O2 to form Na2O2(sodium peroxide). This reaction is very vigorous as sodium burns with a yellow flame The Oxides Of Period 3 Elements Formation of oxides Īll the elements in Period 3 except chlorine and argon combine directly with oxygen to form oxides. The resulting solutions become increasingly acidic. The reactivity of the elements of period 3 towards water thus decreases from Na to Si, and then increases from P to Cl. The resulting solution contains HCl(aq) and is thus acidic (pH = 2). Phosphorus and sulphur do not react with water but chlorine will disproportionate to give an acidic solution: P, S and Cl 2 do not reduce water to hydrogen gas. The resulting solution is weakly alkaline, since the oxide is slightly basic (pH = 9).Īl and Si also react with steam under certain conditions. Mg reacts with cold water very slowly, but can react quickly with steam to give the oxide and hydrogen: The resulting solution is strongly alkaline, and will have a pH of 14. Na reacts vigorously with water to give the hydroxide and hydrogen: Na, Mg, Al and Si are more electropositive than H and can reduce the water to hydrogen gas: The Reaction Of Period 3 Elements With Water
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