Which statement about magnesium is TRUE?

Question

BlackTom AI · Accepted Answer

Question restatement: Which statement about magnesium is TRUE?
Options:
1) The size of Mg2+ is smaller than the size of Na+.
2) Mg has one valence electron.
3) Mg is a alkali metal.
4) Mg bonds with halogens to form polar covalent compounds.
5) Mg has a lower ionization energy than Al.

Option 1 analysis:
- This compares ionic radii: Mg2+ has 2 fewer electrons than Mg, and after losing two electrons its electron configuration resembles Ne. The remaining 10 electrons experience a higher effective nuclear charge, pulling the remaining electron cloud closer and resulting in a smaller ionic radius. In comparison, Na+ has a larger radius because it has more electrons to shield the nucleus. Consequently, Mg2+ is indeed smaller than Na+. This statement is consistent with periodic trends for ionic radii across isoelectronic species.

Option 2 analysis:
- Magnesium is in Group 2 of the periodic table, so its neutral atom has two valence electrons (not one). This misstates the valence electron count and overlooks the typical chemistry of alkaline earth metals, which lose two electrons to form Mg2+. Therefore, this statement is false.

Option 3 analysis:
- Magnesium is not an alkali metal. Alkali metals are in Group 1, such as Li, Na, and K. Magnesium is classified as an alkaline earth metal (Group 2). This incorrect categorization makes the statement false.

Option 4 analysis:
- While magnesium can form bonds with halogens to give magnesium halides, these compounds are predominantly ionic in character (Mg2+ paired with halide anions). Describing the bonding as polar covalent oversimplifies and misrepresents the primary ionic nature of Mg–X bonds in most contexts. Therefore, this statement is not accurate as a general characterization of Mg–halogen bonds.

Option 5 analysis:
- The first ionization energy of magnesium is higher than that of aluminum due to the electronic configuration differences (Mg: [Ne] 3s2; Al: [Ne] 3s2 3p1). Aluminum’s electron is removed from a higher energy 3p orbital with relatively less effective shielding, resulting in a lower ionization energy for Al compared with Mg. Thus, Mg does not have a lower ionization energy than Al; this statement is false.

Summary assessment:
- Option 1 correctly aligns with established ionic radii trends for Mg2+ versus Na+. Options 2, 3, 4, and 5 contain factual inaccuracies or overgeneralizations about magnesium’s valence, metal classification, bonding character, or ionization energy relative to aluminum. The provided response should reflect that option 1 is the true statement, while the rest are incorrect based on fundamental chemical principles.

Which statement about magnesium is TRUE?

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