This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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D. Na_2O < MgO < Al_2O_3 Step 1: Identify the type of bonding and factors affecting melting point. The oxides of sodium (Na_2O), magnesium (MgO), and aluminum (Al_2O_3) are all ionic compounds. The melting point of ionic compounds is primarily determined by the strength of the ionic bonds, which is quantified by lattice energy. Lattice energy is directly proportional to the product of the charges of the ions and inversely proportional to the distance between their centers (ionic radii). Step 2: Determine the charges of the ions in each oxide. • In Na_2O, the ions are Na^+ and O^2-. The product of absolute charges is |(+1) × (-2)| = 2. • In MgO, the ions are Mg^2+ and O^2-. The product of absolute charges is |(+2) × (-2)| = 4. • In Al_2O_3, the ions are Al^3+ and O^2-. The product of absolute charges is |(+3) × (-2)| = 6. Step 3: Compare the ionic radii of the cations. Sodium (Na), magnesium (Mg), and aluminum (Al) are all in the same period (Period 3) of the periodic table. For cations in the same period, the ionic radius decreases as the nuclear charge increases (from left to right). Therefore, the order of increasing ionic radius is Al^3+ < Mg^2+ < Na^+. Step 4: Determine the order of increasing melting points. A higher product of charges and smaller ionic radii lead to stronger electrostatic attraction between ions, resulting in higher lattice energy and thus higher melting points. • Na_2O has the lowest charge product (2) and the largest cation (Na^+), leading to the weakest ionic bonds and lowest melting point. • MgO has a higher charge product (4) and a smaller cation (Mg^2+) than Na_2O, resulting in stronger bonds and a higher melting point. • Al_2O_3 has the highest charge product (6) and the smallest cation (Al^3+), leading to the strongest ionic bonds and highest melting point. Therefore, the order of increasing melting point is Na_2O < MgO < Al_2O_3. The final answer is D. That's 2 down. 3 left today — send the next one.