2. The elements sodium to argon form the third period of the periodic table - Scottish Highers Chemistry - Question 2 - 2018

The structure of sulfur chloride (SCl₂) should be circled, as it contains bonds with the lowest polarity due to the similar electronegativities of sulfur and chlorine.

Silicon tetrachloride (SiCl₄) is the most soluble in hexane due to its non-polar covalent nature. Hexane is also non-polar, and according to the principle of "like dissolves like", the similar polarity of these two compounds allows for favorable interactions, making silicon tetrachloride highly soluble in hexane. In contrast, the other chlorides are either more polar or have dipole moments that hinder their solubility in non-polar solvents.

Silicon nitride (Si₃N₄) has a high melting point due to its covalent network structure. In this structure, each silicon atom bonds covalently to nitrogen atoms, creating a three-dimensional lattice that requires substantial energy to break these strong covalent bonds during melting. Additionally, the compact arrangement of atoms in this network contributes to its stability and high melting point.

To calculate the atom economy, you first need to find the molar mass of the desired product, silicon nitride (Si₃N₄), and divide it by the total mass of all reactants. The molar masses are as follows: Si = 28.1 g/mol, N = 14.0 g/mol. Therefore, the molar mass of Si₃N₄ is:

$ext{Molar mass of Si₃N₄} = 3(28.1) + 4(14.0) = 84.3 + 56.0 = 140.3 ext{ g/mol}$

Now adding the reactants:

35Cl + 16N₃ = 35 + 16(14.0) = 35 + 224 = 259 g/mol

Thus, the atom economy is calculated as follows:

$ext{Atom Economy} = \left( \frac{\text{Molar Mass of Si₃N₄}}{\text{Total mass of reactants}} \right) \times 100 = \left( \frac{140.3}{259} \right) \times 100 \approx 54.1\%$

A diagram showing a flask connected to a delivery tube leading from the source of chlorine gas and having an apparatus to collect aluminium chloride and allow unreacted chlorine gas to escape should be drawn. Labels will include the flask, delivery tube, hot aluminium foil, and the collection point.

The aluminium foil needs to be heated initially to provide the necessary activation energy to initiate the reaction with chlorine. Although the reaction is exothermic, starting it requires overcoming the activation energy barrier for the reaction to commence.