Which one in this pair has the larger radius? Explain
a. Calcium atom or calcium ion
b. Aluminum ion or Magnesium ion
Calcium ion has the two outside electrons removed; therefore, it should be smaller than the atom.
Aluminum ion has a +3 charge on it while Mg ion has just +2; therefore, the protons in the nucleus of Al exert a greater pull on its electrons than Mg and the Al ion should be smaller.
a. Calcium atom or calcium ion:
The calcium atom, Ca, has a larger radius compared to the calcium ion, Ca2+.
When an atom loses one or more electrons to become an ion, it undergoes a process called ionization. In the case of calcium, it loses two electrons to form the Ca2+ ion.
The loss of electrons reduces the electron cloud surrounding the nucleus, resulting in the calcium ion having a smaller radius compared to the calcium atom. As the positive charge of the nucleus remains the same while the number of electrons decreases, the attraction between the nucleus and remaining electrons becomes stronger, causing the electron cloud to contract.
b. Aluminum ion or Magnesium ion:
The aluminum ion, Al3+, has a smaller radius compared to the magnesium ion, Mg2+.
Aluminum loses three electrons to form the Al3+ ion, while magnesium loses two electrons to form the Mg2+ ion.
Similar to the explanation above, the loss of electrons in both cases leads to a reduction in the electron cloud's size. However, since aluminum loses three electrons compared to magnesium's loss of two electrons, the net positive charge in the aluminum ion is greater. This increased positive charge in the nucleus attracts the remaining electrons more strongly, resulting in a smaller radius for the aluminum ion.
To determine which one in each pair has the larger radius, we need to understand the concept of atomic and ionic radii.
a. Calcium atom or calcium ion:
In a calcium atom, the number of protons in the nucleus is equal to the number of electrons orbiting around it. Since the atom is electrically neutral, the number of electrons equals the number of protons. However, when calcium loses two electrons, it forms a calcium ion with a +2 charge.
When an atom loses or gains electrons to form an ion, the electron configuration changes, affecting the size of the electron cloud. In the case of the calcium ion, it loses two electrons, resulting in a smaller electron cloud compared to the calcium atom. Therefore, the calcium ion has a smaller radius than the calcium atom.
b. Aluminum ion or Magnesium ion:
Similarly, let's compare the aluminum ion and the magnesium ion. An aluminum atom has three electrons in its outermost energy level, while a magnesium atom has two electrons in its outermost energy level. These atoms can achieve a more stable electron configuration by losing these outermost electrons, forming aluminum ion with a +3 charge and magnesium ion with a +2 charge.
Since the aluminum ion has lost more electrons compared to the magnesium ion, it has a smaller electron cloud and, consequently, a smaller radius. Therefore, the aluminum ion has a smaller radius than the magnesium ion.
In summary:
a. The calcium ion has a smaller radius than the calcium atom.
b. The aluminum ion has a smaller radius than the magnesium ion.