Question

rank the following atoms in order of increasing size (i.e., smallest to largest): li, mg, be, ba, o. answer: a li < mg < be < ba < o b ba < mg < li < be < o c li < be < o < mg < ba d o < be < li < mg < ba e o < li < be < ba < mg

Explanation:

Atomic size trends:

• Across a period (left to right): decreases due to increased nuclear charge attracting electrons closer.
• Down a group: increases as electron shells are added.
• Oxygen (\(O\)) is in period 2. Beryllium (\(Be\)) and lithium (\(Li\)) are also in period 2. But \(O\) has a smaller size than \(Be\) and \(Li\) as it is further to the right. \(Li\) is to the left of \(Be\) in period 2, so \(Li>Be\) (size).
• Magnesium (\(Mg\)) is in period 3 (below \(Be\) in group 2). So \(Mg > Be\).
• Barium (\(Ba\)) is in period 6 (below \(Mg\) in group 2). So \(Ba>Mg\).

Answer:

D. \(O < Be < Li < Mg < Ba\)