Determine which is larger member of each pair A) Mg2+ or Al3+ B) N3- or O2-? Explain
A. The higher charge on Al^3+ causes the protons to pull in the outside electrons more than the smaller 2+ charge of Mg^2+; therefore, the Al^3+ will be smaller than Mg^2+.
B. Both N^3- and O^2- have extra electrons in their outer shells but those extra electrons, each carrying a negative charge repel each other; therefore, the N^3- ion should be the large of the two.
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To determine which ion is larger in each pair, you need to compare their atomic sizes and charges. Here's how you can analyze each pair:
A) Mg2+ or Al3+
1. Look at the atomic number of each element. Magnesium (Mg) has an atomic number of 12, while aluminum (Al) has an atomic number of 13.
2. Compare the charges of the ions. Mg2+ has a charge of +2, indicating the loss of two electrons. Al3+ has a charge of +3, indicating the loss of three electrons.
3. Consider the trend in atomic size. Moving across a period in the periodic table, atomic size generally decreases due to increasing nuclear charge. However, going down a group, atomic size tends to increase as new energy levels are added.
4. Analyze both factors. Based on their atomic numbers, aluminum has more protons and electrons than magnesium, suggesting a smaller size for Al3+. However, considering the charge, Al3+ lost three electrons, resulting in less electron-electron repulsion, allowing the ion to contract further.
5. Consider the overall effect. The smaller atomic size of aluminum is offset by the greater positive charge on Al3+, which attracts electrons more strongly, resulting in a smaller ion compared to Mg2+.
Conclusion: Al3+ is generally smaller than Mg2+.
B) N3- or O2-
1. Look at the atomic number of each element. Nitrogen (N) has an atomic number of 7, while oxygen (O) has an atomic number of 8.
2. Compare the charges of the ions. N3- has a charge of -3, indicating the gain of three electrons. O2- has a charge of -2, indicating the gain of two electrons.
3. Consider the trend in atomic size. Similar to the previous pair, moving across a period, atomic size generally decreases, but moving down a group, atomic size tends to increase.
4. Analyze both factors. Nitrogen has fewer protons and electrons compared to oxygen, suggesting a larger size for N3-. However, considering the charge, N3- has gained three electrons, leading to increased electron-electron repulsion and expansion of the ion.
5. Consider the overall effect. Despite having fewer protons and electrons, the larger size caused by electron-electron repulsion makes N3- generally larger than O2-.
Conclusion: N3- is generally larger than O2-.
In summary, when comparing the ion sizes, Al3+ is generally smaller than Mg2+, and N3- is generally larger than O2-.