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The elements sodium to argon form the third period of the periodic table - Scottish Highers Chemistry - Question 2 - 2018
Question 2
The elements sodium to argon form the third period of the periodic table. (a) Explain the decrease in atom size going across the third period from sodium to argon. ... show full transcript
Worked Solution & Example Answer:The elements sodium to argon form the third period of the periodic table - Scottish Highers Chemistry - Question 2 - 2018
Step 1
Explain the decrease in atom size going across the third period from sodium to argon.
Answer
The decrease in atomic size from sodium to argon across the third period can be attributed to the increasing number of protons in the nucleus. As more protons are added, the nuclear charge increases, pulling the electrons closer to the nucleus. This results in a reduced atomic radius. Additionally, the effective nuclear charge felt by the outermost electrons also increases, leading to a stronger attraction between the nucleus and the electrons, thereby decreasing the atomic size.
Step 2
Step 3
Explain fully why, of these three chlorides, silicon tetrachloride is the most soluble in hexane.
Answer
Silicon tetrachloride (SiCl₄) is the most soluble in hexane because both substances are non-polar. Hexane is a non-polar solvent, which allows the non-polar molecules of silicon tetrachloride to mix readily. In contrast, sulfur chloride (SCl₂) and phosphorus trichloride (PCl₃) have some polar character which makes them less soluble in non-polar solvents like hexane.
Step 4
Explain fully, in terms of structure and bonding, why silicon nitride has a high melting point.
Answer
Silicon nitride (Si₃N₄) has a high melting point due to its covalent network structure. In this structure, silicon and nitrogen atoms are bonded through strong covalent bonds, forming a rigid lattice. Breaking these strong covalent bonds requires a significant amount of energy, resulting in a high melting point. Additionally, there are no free electrons for conduction when molten, which further contributes to its physical stability.
Step 5
Calculate the atom economy for the formation of silicon nitride.
Answer
To calculate the atom economy for the formation of silicon nitride, we first identify the molar masses involved:
- Molar mass of Si₃N₄ = 140.3 g/mol
- Total mass of reactants = 35Cl + 16N₂ + 12NH₃ = 170 g + 16 g + 140 g = 302 g
Atom Economy = (mass of desired product / total mass of reactants) × 100 = (140.3 g / 302 g) × 100 = 46.4%. Hence, the atom economy for the formation of silicon nitride is approximately 46.4%.
Step 6
Complete a labelled diagram to show an apparatus suitable for carrying out this preparation.
Answer
The diagram should include a flask connected to a delivery tube, where chlorine gas is passed over heated aluminium. The flask should also have an outlet for any unreacted chlorine gas to escape, and labels should identify the hydroxyl acid, sodium hypochlorite, heated aluminium, and the exit for chlorine gas.
Step 7
Explain why the aluminium foil needs to be heated at the start of the preparation, despite the reaction being highly exothermic.
Answer
The aluminium foil needs to be heated to provide initial activation energy for the reaction with chlorine gas. Although the reaction is exothermic, it requires sufficient energy to overcome the activation barrier to initiate the reaction. Heating the aluminium ensures that it readily reacts with the chlorine, producing aluminium chloride efficiently.