The alkali metal ions are very important for the proper functioning of
biologic systems, such as nerves and muscles, and \(\mathrm{Na}^{+}\) and
\(\mathrm{K}^{+}\) ions are present in all body cells and fluids. In human blood
plasma, the concentrations are
$$
\left[\mathrm{Na}^{+}\right] \approx 0.15 M \text { and
}\left[\mathrm{K}^{+}\right] \approx 0.005 M
$$
For the fluids inside the cells, the concentrations are reversed:
$$
\left[\mathrm{Na}^{+}\right] \approx 0.005 M \text { and
}\left[\mathrm{K}^{+}\right] \approx 0.16 M
$$
Since the concentrations are so different inside and outside the cells, an
elaborate mechanism is needed to transport \(\mathrm{Na}^{+}\) and
\(\mathrm{K}^{+}\) ions through the cell membranes. What are the ground-state
electron configurations for \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{+}\) ? Which ion
is smaller in size? Counterions also must be present in blood plasma and
inside intracellular fluid. Assume the counterion present to balance the
positive charge of \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{+}\) is
\(\mathrm{Cl}^{-}\). What is the ground-state electron configuration for
\(\mathrm{Cl}^{-}\) ? Rank these three ions in order of increasing size.