s-block energetics

The three energy steps that turn the alkali and alkaline-earth metals into hydrated ions — atomisation, ionisation and the cycle-derived hydration enthalpy — with the ΔH°, ΔG° of their reactions with water and their standard potentials.


$\ce{Li}$	$\ce{Li+}$	159.3	520.2	−278.49	−519	−222.7	−213.4	−3.040	157
$\ce{Na}$	$\ce{Na+}$	107.5	495.8	−240.12	−404	−184.3	−182.0	−2.710	191
$\ce{K}$	$\ce{K+}$	89.0	418.8	−252.38	−321	−196.5	−203.4	−2.931	235
$\ce{Rb}$	$\ce{Rb+}$	80.9	403.0	−251.17	−296	−195.3	−204.1	−2.980	250
$\ce{Cs}$	$\ce{Cs+}$	76.5	375.7	−258.28	−271	−202.4	−212.1	−3.026	272
$\ce{Be}$	$\ce{Be^2+}$	324.0	2656.6	−382.80	−2485	−271.1	−219.9	−1.847	112
$\ce{Mg}$	$\ce{Mg^2+}$	147.1	2188.4	−466.85	−1924	−355.2	−295.0	−2.372	160
$\ce{Ca}$	$\ce{Ca^2+}$	177.8	1735.3	−542.83	−1578	−431.2	−393.8	−2.868	197
$\ce{Sr}$	$\ce{Sr^2+}$	164.4	1613.7	−545.80	−1446	−434.1	−399.7	−2.899	215
$\ce{Ba}$	$\ce{Ba^2+}$	180.0	1468.1	−537.64	−1308	−426.0	−401.0	−2.912	224

Hydration enthalpies are single-ion values derived from formation enthalpies with the convention ΔhydH°(H⁺) = −1091 kJ/mol. ΔH° and ΔG° with water are per mole of metal and assume the hydroxide stays dissolved (untrue for Be and Mg). The CRC potential of Rb (−2.98 V) is slightly more negative than the −2.943 V implied by the NBS ΔfG°.

Sources

D. D. Wagman et al., “The NBS tables of chemical thermodynamic properties”, J. Phys. Chem. Ref. Data 11, Suppl. 2 (1982) (ΔfH°, ΔfG° of the ions).
J. D. Cox, D. D. Wagman, V. A. Medvedev, CODATA Key Values for Thermodynamics (1989), via the CRC Handbook (atomisation enthalpies).
A. Kramida et al., NIST Atomic Spectra Database, ver. 5.11 (ionisation energies).
P. Vanýsek, “Electrochemical series”, CRC Handbook of Chemistry and Physics, 91st ed. (2010).
A. F. Wells, Structural Inorganic Chemistry, 5th ed. (1984) (metallic radii, 12-coordination).

Used in these lessons

Hydrogen and the s-block