Question

Use the periodic table to compare the sizes of ionic radii with the corresponding atomic radii or other ionic radii. Choose from smaller and larger in the blanks below:

A sodium cation is
than a sodium atom.
A phosphorus anion is
than a phosphorus atom.
A magnesium ion is
than a sodium ion.
A chlorine ion is
than a phosphorus ion.
A potassium ion is
than a sodium ion.

Answer 1

A sodium cation is smaller than a sodium atom. (Loss of an electron reduces electron-electron repulsion and the remaining electrons are held more tightly.)

A phosphorus anion is larger than a phosphorus atom. (Gain of electrons increases electron-electron repulsion and expands the electron cloud.)

A magnesium ion is smaller than a sodium ion. (Mg2+ and Na+ are isoelectronic, but Mg2+ has a higher nuclear charge pulling electrons in more tightly.)

A chlorine ion is smaller than a phosphorus ion. (Cl− and P3− are isoelectronic, but Cl− has a higher nuclear charge so its radius is smaller.)

A potassium ion is larger than a sodium ion. (Both are +1 cations, but size increases down the group, so K+ > Na+.)