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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
As we move across the third period from sodium to argon, the atomic number increases, resulting in a greater number of protons in the nucleus. This leads to an increased positive charge, which pulls the electrons closer to the nucleus, thereby decreasing the atomic radius. Additionally, since electrons are being added to the same principal energy level, there is minimal shielding effect, allowing the nucleus to exert a stronger attractive force on the electron cloud.
Step 2
Step 3
Explain fully why, of these three chlorides, silicon tetrachloride is the most soluble in hexane.
Answer
Silicon tetrachloride (SiCl₄) is non-polar due to its symmetrical tetrahedral shape, causing the dipoles to cancel out. Hexane is also a non-polar solvent. According to the principle 'like dissolves like,' silicon tetrachloride will dissolve well in hexane because they both share similar non-polar characteristics.
Step 4
Explain fully, in terms of structure and bonding, why silicon nitride has a high melting point.
Answer
Silicon nitride (Si₃N₄) exhibits a covalent network structure, where each silicon atom is bonded to nitrogen atoms through strong covalent bonds, forming a rigid three-dimensional lattice. High energy is required to break these strong covalent bonds, resulting in a high melting point of 1900 °C. Additionally, the strong interactions within the lattice contribute significantly to the stability of the structure when molten.
Step 5
Calculate the atom economy for the formation of silicon nitride.
Answer
To calculate the atom economy, use the formula:
ext{Atom Economy} = rac{ ext{Mass of Desired Product}}{ ext{Total Mass of Reactants}} imes 100
Given:
- Mass of ( Si_3N_4 ) = 140.3 g
- Mass of total reactants = (3 × 170) + (16 × 17) = 510 + 272 = 782 g
Thus,
Therefore, the atom economy for the formation of silicon nitride is approximately 17.94%.
Step 6
Complete a labelled diagram to show an apparatus suitable for carrying out this preparation.
Answer
A diagram should include a boiling flask connected to a condenser, with hydrochloric acid and sodium hypochlorite being heated in the flask. Labels should indicate: 'Hydrochloric Acid' on one side, 'Sodium Hypochlorite' on the other, and 'Aluminium Foil' where the gas passes over the heated foil.
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 initially to provide sufficient activation energy for the reaction to proceed. Even though the reaction is exothermic, the activation energy is necessary to initiate the reaction, allowing chlorine gas to react effectively with the heated aluminium, forming aluminium chloride.