Which one pair has the larger radius?Explain?
a. Calcium atom or calcium ion
b. Aluminum ion or Magnesium ion
Ca atom is 1s2 2s2 2p6 3s2 3p6 4s2
Ca^+2 = 1s2 2s2 2p6 3s2 3p6
The Ca ion is missing the last two electrons; wouldn't you expect the radius to be smaller?
Look at the electron configuration of Mg ion versus Al ion, then compare the nuclear charge of Al ion vs Mg ion on the pull of their outside electrons.
To determine which pair has the larger radius, we need to understand the concept of atomic radius and how it changes when an atom gains or loses electrons.
Atomic radius refers to the size of an atom, specifically the distance from its nucleus to the outermost electron shell. As we move across a period (horizontal row) in the periodic table, the atomic radius generally decreases, while moving down a group (vertical column) leads to an increase in atomic radius.
Now let's analyze each pair:
a. Calcium atom or calcium ion:
A calcium atom has 20 protons, 20 electrons, and 20 neutrons. When calcium loses two electrons, it forms a calcium ion, Ca2+. By losing two negatively charged electrons, the overall charge of the calcium ion increases, but the number of protons remains the same at 20. Since the number of protons determines the attraction between the electrons and the nucleus, the electron cloud of the calcium ion is more strongly pulled towards the nucleus compared to the calcium atom. As a result, the radius of the calcium ion is smaller than that of the calcium atom.
b. Aluminum ion or magnesium ion:
An aluminum atom has 13 protons, 13 electrons, and 14 neutrons. When aluminum loses three electrons, it forms an aluminum ion, Al3+. Similarly, a magnesium atom has 12 protons, 12 electrons, and 12 neutrons. When magnesium loses two electrons, it forms a magnesium ion, Mg2+. In both cases, the loss of electrons results in an increase in the overall charge, but the number of protons remains the same. Consequently, the radius of the aluminum ion is smaller than that of the aluminum atom, and the radius of the magnesium ion is smaller than that of the magnesium atom.
To summarize, in both pairs, the ions have a smaller radius compared to the atoms from which they are derived. These smaller radii are due to the increased effective nuclear charge resulting from the loss of electrons.