Experiment 1 -Period 3

Introduction Across the element of period 3, it contains sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine and argon. For sodium and magnesium, they are the members of the s-block of the periodic table while the rest are the members of the p-block. There are the oxides of metal and non-metals. Structurally they are covalent and ionic compounds. The elements in period 3 except chlorine and argon combine directly with oxygen to form oxides. Na2O is an ionic oxide. The reaction with oxygen is very vigorous as sodium burns with a yellow flame. 4Na(s) + O2(g) → 2Na2O(s). MgO is also an ionic oxide. The reaction is vigorous with a brilliant white flame forming a white ash of magnesium oxide. 2Mg(s) + O2(g) → 2MgO(s). Al2O3 is mostly ionic but there is significant covalent character. The reaction is initially vigorous. 4Al(s) + 3O2(g) → 2Al2O3(s). SiO2 is a giant covalent oxide that the reaction is slow. Si(s) + O2(g) → SiO2(s). For the formation of phosphorus oxide,it is a vigorous reaction forming masses of white fumes of phosphorus (V) oxide P4O10 which is a molecular covalent oxide. The oxidation number of P in this oxide is +5. P4(s) + 5O2(g) → P4O10(s). SO2 is a molecular covalent oxide. Sulphur melts easily and burns with a blue flame forming sulphur (IV) oxide, a colourless gas with a choking odour. S(s) + O2(g) → SO2(g). Chlorine cannot combine directly with oxygen to form oxide. To prepare Cl2O, react chlorine gas with hydrated sodium carbonate at 20 – 30 °C. 2 Cl2 + 2 Na2CO3 + H2O → Cl2O + 2 NaHCO3 + 2 NaCl. While argon is noble gas, it is not reactive so it cannot form oxide. Across period 3 oxides, the melting point and the boiling point will change base on the structure and the bonding of the oxides. The trend of structure and bonding of the oxides is from giant struxture of ions on the left of the period then the giant covalent oxide in the middle to the simple molecular oxide on the right. The acidbase nature of the oxides are basically from strongly basic and will have gradually decrease in Ph when going across period from left to right via an amphoteric axid in the middle and end with a strongly acidic property.In this experiment, we did some simple observations and tests to find out the differences between different types of oxides. We studied the reaction of period 3 oxide react with water , the observation on the solubility of period 3 oxide and the acid-base nature of period 3 oxide was made. Not only that, through this experiment we can further understands more about period 3 oxides for example like the melting and boiling point, the structure and bonding and other properties of period 3 oxides.

Discussion: During the experiment, we added the period 3 oxides to water and the reaction was observed. For sodium peroxide, it dissolve readily and colourless alkaline solution is formed while for magnesium oxide, it only slightly soluble in water and white precipitate can be seen in the alkaline solution. In this two reaction, hydrated ions are formed when ionic compounds dissolve in water. When sodium oxide and magnesium oxide dissolve in water, the small highly charged oxide ions strongly attract to the water molecules so after hydration there is hydrolysis to produce hydroxide ions : Na2O2 (aq) + H2O(l) → 2NaOH(aq), MgO + H2OMg(OH)2. For silicon dioxide, it does not dissolve in water. the structure of silicon dioxide is an extended network of SiO4 units. Each central silicon atom is bonded covalently to four oxygen atoms, but it only has a half share in four atoms. Silicon dioxide does not react with water due to the thermodynamic difficulty of breaking to its network covalent structure. For non-metallic oxides reaction with water like phosphorus,it is a very exothermic reaction on adding to water to produce an acidic solution. It reacts vigorously with water and can be used as a powerful dehydrating agent. Various acids depending upon the amount of water used but in excess of water,tetraoxophosphoric (V) acid is formed : P4O10(s) + 6H2O(l) → 4H3PO4(aq). For sulphur, the sulphur gas dissolves readily in water to produce a colourless acidic solution. SO2(g) + H2O(l) → H2SO3(aq) Anyway,there is two oxides of period 3 react with water that is not carried out during the experiment which is dichlorine oxide and aluminium oxide.Dichlorine oxide, Cl2O, reacts with water to produce chloric(I) acid: Cl2O(g) + H2O(l) → 2HClO(aq). Aluminium oxide has a special properties which are the intermediate between those of a metallic oxide and those of nonmetallic oxide.When it react with water, it can act as acid or base. Al2O3(s) + 6H+ (aq) + 3H2O(l) → 2[Al(H2O)6] 3+ (aq) (base) Al2O3(s) + 2OH– (aq) + 3H2O(l) → 2[Al(OH)4] – (aq) (acid) Going across period 3, Sodim peroxide,magnesium oxide and aluminium oxide will have a giant ionic structure containing metal ions and oxide ions. They consist of ionic bond as the metal have low ionization energy will loses their electron and becoming positively charged where non-metal have high electron affinity where it gains electron becoming negatively charged to form a strong electrostatic attraction between each other. So, both of the charged ions will

attract each other by a strong electrostatic force forming the ionic bond. The ionic bond is formed by transferring of electrons. Silicon dioxide is a giant covalent structure and it will form covalent bonds. This is because there is insufficient of electronegativity difference between oxygen and silicon to form ionic bond. For oxide like phosphorus pentoxide, sulphur dioxide and chorine(i) oxide, they are simple molecular structure which held together by intermolecular Van der Waals forces. Generally, we can see that from sodium peroxide to Chlroine(i) oxide,the structure change from giant ionic structure to giant covalent structure then to simple molecular strucute while the bonding is change form ionic to covalent bonds.Across period 3 oxides, the metal oxides (sodium peroxide,Na2O2, magnesium oxide,MgO, aluminium oxide Al2O3) and silicon dioxide SiO2 have a higher melting and boiling points. This is because the above elements are giant ionic and giant molecules, they are held strongly by ionic and covalent bonds. A lot of energy is needed to break the ionic and covalent bonds. While oxides of phosphorus, sulphur and chlorine are simple and small molecules. The attractive forces between these molecules are Van der Waals dispersion and dipole-dipole interactions which will vary depending on the size, shape and polarity of the different molecules but Van der Waals and dipole-dipole interactions are much weaker compared to ionic or covalent bonds in a giant structure. That is why, oxides of phosphorus, sulphur and chlorine having a lower melting point compare to the oxides of sodium,magnesium,aluminium and silicon. For the trend of acid-base behavior of period 3 oxides, it begin with strongly basic from the left which is sodium peroxide and magnesium oxide then to aluminium oxide which is amphoteric (can act as acid or base) then end with strongly acidic on the right which is phosphorus pentoxide,sulphur dioxide and chlorine (i) oxide. Sodium oxide is a strong base as it contain oxide ion, O2- and it have a high tendency to combine with hydrogen ioins. Magnesium oxide is a simple basic oxide compared to sodium peroxide because the oxide ions are not so free as the ions in sodium peroxide. Aluminium oxide is emphoteric and it act as base and acid. Silicon dioxide has no basic properties because it have no oxide ions. It is a very weak acidic and it doesn’t react with water because it is hard to break the giant covalent structure. Phosphorus pentoxide react vigorously with water to form a solution containing a mixture of acids. and as the same to sulphur dioxide, it react with water to give a acidic solution of sulphuric (IV) acid.

For chlorine (I) oxide, it react with water to form a strong acidic solution as it has no doubly-bonded oxygen and no way of delocalizing the charge over the negative ion formed by loss of the hydrogen. It simply means that the negative ion is not stable and readily reclaims its hydrogen to revert to the acid. Atoms increase its electronegativity as the atomic number increase across the period from left to right. Na and Mg are electopostive and have a giant ionic structure so it lose electrons and form positive ions. It will make oxygen atoms to form oxide ions which is a strong base and easily combine with hydrogen ions. O2- + H+ ---> OH- So it contribute sodium peroxide and magnesium oxide a base nature. Al is not so electropositive and aluminium oxide consist of some covalent character. Oxide ions are not well formed and a.o is only just able to accept protons from acid or oxide ions combine with hydrogen ions. While Si, P, S and Cl are increasing its electronegativity. They are not able to form oxide ions so the atoms of these elements in the oxides accept paris of electrins form oxygen in water so they behave as acids. For example SO2 +H2O ---> H2SO3. So as the atomic number increase, elctronegavity increase then the acidic level also increase. Precautions steps are taken during the experiment to ensure our safety. First, when handling corrosive chemicals for example like conectrated sulphuric acid, gloves are wore to avoid any contact of bare hand with the corrosive chemicals. Then, when we are preparing the sulphur dioxide gas, a chocking smell was released and we were cautions to not breath in too much og sulphur dioxide gas as it is not so good to our body too. Conclusion: Period 3 oxides