Question: Using the periodic table to locate each element, write theelectron configuration of (a) Os (b) Co (c) Ag.

The distribution of electrons in atomic or molecular orbitals of an atom, molecule, or other physical structure is known as electron configuration.

(a) Based on the periodic table, Os has the atomic number of$76$, therefore it has $76$electrons with electron configuration:

$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^{10}4{\mathrm{p}}^{6}5{\mathrm{s}}^{2}4{\mathrm{d}}^{10}5{\mathrm{p}}^{6}6{\mathrm{s}}^{2}4{\mathrm{f}}^{14}5{\mathrm{d}}^7$or$\left[\mathrm{Xe}\right]6{\mathrm{s}}^{2}4{\mathrm{f}}^{14}5{\mathrm{d}}^6$.

(b) Based on the periodic table, Co has the atomic number of $27$, therefore it has $27$electrons with this electron configuration:

$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^7$or$\left[\mathrm{Ar}\right]4{\mathrm{s}}^{2}3{\mathrm{d}}^7$.

(c) Based on the periodic table, Ag has the atomic number of $47$, therefore it has $47$electrons with electron configuration:

$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^{10}4{\mathrm{p}}^{6}5{\mathrm{s}}^{1}4{\mathrm{d}}^{10}$or$\left[\mathrm{Kr}\right]5{\mathrm{s}}^{1}4{\mathrm{d}}^{10}$.

Instead of having a full 5s orbital, the atom is more stable when the d-orbital is fully filled.