Recently in the Chemistry.SE chatroom a user posted this to celebrate the New Year:
Can Ca and K exist as an ionic compound? If not, why is it impossible?
Ca with atomic number 20, K 19 so 2019 ->Happy New Year->2020
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As a creator of this memetic illustration, I feel obliged to post a brief answer.
The Ca-K system was found by Klemm and Kunze [67Kle] to exhibit virtually complete immiscibility in both solid and liquid states. No compounds were found by X-ray diffraction.
*67Kle: W. Klemm and D. Kunze, "Systems of Alkali and Alkaline Earth Metals," Proc. Int'l. Symp. on Alkali Metals, London Chem. Soc., Special Publ. No. 22, 3-22 (1967). (Equi Diagram; Experimental; #)
No for a couple of reasons:
Ionic bonds are between a metal and a non-metal - Ca and K are both metals.
K and Ca have a difference of .18 in the Pauling Scale - and definitions of ionic bonds are often stated as having above a 1.7 difference.
Both atoms, Ca and K, aim to lose their electrons to form a full valence(thus forming cations) and have negative oxidation numbers.