Question

the atomic number of beryllium (be) is 4, and the atomic number of barium (ba) is 56. which comparison is best supported by this information?

• they are in the same group because they have similar atomic masses, but they are in different periods because they have different chemical properties.
• they are in the same group because they have similar chemical properties, but they are in different periods because they have very different atomic numbers.
• they are in the same group because their atomic numbers are each multiples of four, but they are in different periods because they have different chemical properties.
• they are in the same group because they have similar atomic masses, but they are in different periods because they have very different atomic numbers.

Explanation:

To solve this, we recall periodic table concepts: Elements in the same group (vertical column) have similar chemical properties (due to same valence electron configuration), and periods are horizontal rows where atomic number increases. Beryllium (Be, atomic number 4) and Barium (Ba, atomic number 56) are both alkaline earth metals (Group 2), so they have similar chemical properties. Atomic number determines period (higher atomic number means higher period), so different atomic numbers mean different periods. Let's analyze each option:

• Option 1: Wrong. Same group is due to similar chemical properties, not atomic masses. Also, same - group elements have similar chemical properties.
• Option 2: Correct. Same group (Group 2) because of similar chemical properties (alkaline earth metals), different periods because atomic numbers (4 vs 56) differ (Be is in period 2, Ba in period 6).
• Option 3: Wrong. Same group is not because atomic numbers are multiples of 4 (this is an incorrect reasoning). And same - group elements have similar chemical properties.
• Option 4: Wrong. Same group is due to similar chemical properties, not atomic masses.

Answer:

B. They are in the same group because they have similar chemical properties, but they are in different periods because they have very different atomic numbers.