Question

7 atoms of elements in the same group of the periodic table share the same a atomic numbers b atomic masses c number of valence electrons d number of energy levels

Explanation:

• Atomic number: Defined by the number of protons in an atom. Different elements (even in the same group) have different atomic numbers. For example, hydrogen (\(H\), atomic number \(1\)) and lithium (\(Li\), atomic number \(3\)) are in different groups, but if we consider a group like alkali metals (Group 1), sodium (\(Na\), atomic number \(11\)) and potassium (\(K\), atomic number \(19\)) have different atomic numbers.
• Atomic mass: Depends on the sum of protons and neutrons. Elements in the same group have different isotopes and thus different atomic masses. For instance, in Group 1, the atomic mass of \(Na\) is approximately \(22.99\space g/mol\) and that of \(K\) is approximately \(39.10\space g/mol\).
• Number of valence electrons: The periodic table groups are based on the number of valence electrons. Group 1 elements (alkali metals) all have \(1\) valence electron, Group 2 (alkaline - earth metals) have \(2\) valence electrons, Group 17 (halogens) have \(7\) valence electrons.
• Number of energy levels: Increases as we move down a group. For example, in Group 1, \(H\) has \(1\) energy level (\(n = 1\)), \(Li\) has \(2\) energy levels (\(n=1,2\)), \(Na\) has \(3\) energy levels (\(n = 1,2,3\)).

Answer:

C. number of valence electrons