Calculate the enthalpies of formation, ΔHf∘, of the group 1 fluoride compounds from their elements using the Born–Haber cycle. Process H∘, /
sublimation of K(s) 90
sublimation of Cs(s) 78
dissociation of F2(g) 158
ionization energy of K(g) 419
ionization energy of Cs(g) 376
electron affinity of F(g) −322
lattice enthalpy of KF(s) 821
lattice enthalpy of CsF(s) 750

Enthalpy of formation of KF = -555 kJ/mol

Enthalpy of formation of CsF = -539kJ/mol

Explanation:

Explanations are provided in the attachment below

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.