Question

storyline 1 exam
a calcium ion is formed from a calcium atom. how do the sizes of the calcium atom and calcium ion compare to one another?
the calcium ion is larger than the calcium atom because the same number of protons now attract a fewer number of electrons
the calcium ion is larger than the calcium atom because the same number of protons now attract a greater number of electrons
the calcium ion is smaller than the calcium atom because the same number of protons now attract a fewer number of electrons
the calcium ion is smaller than the calcium atom because the same number of protons now attract a greater number of electrons

Explanation:

Calcium atom (\(Ca\)) has the electron configuration \([Ar]4s^{2}\). When it forms a calcium ion (\(Ca^{2+}\)), it loses 2 electrons from the \(4s\) orbital. The number of protons in the nucleus remains the same (20 protons for \(Ca\)). With fewer electrons (now 18 electrons for \(Ca^{2+}\) instead of 20 for \(Ca\)), the same number of protons can pull the remaining electrons closer to the nucleus. According to the concept of ionic and atomic radius, when an atom loses electrons to form a cation, the radius decreases because the effective nuclear charge (the net positive charge experienced by an electron) increases (fewer electrons to be attracted by the same number of protons).

Answer:

The calcium ion is smaller than the calcium atom because the same number of protons now attract a fewer number of electrons.