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

  • 2
    $\begingroup$ No.$\mathstrut$ $\endgroup$ Jan 5, 2020 at 7:30
  • 7
    $\begingroup$ Guys, seriously? I came up with this in five minutes in the middle of the night on Jan 1st and I already had to explain myself in chat on Chemistry.SE and then in chat on English.SE. It's illiterate and makes no chemical sense and was only made for the sake of creating a non-standard congratulation keeping a LaTeX compiler busy at the new year's eve:) $\endgroup$
    – andselisk
    Jan 5, 2020 at 7:51
  • 2
    $\begingroup$ I'm voting to close this question as off-topic because it is not chemistry, it is about a joke in chemistry which is about arranging symbols to make a word or slogan $\endgroup$ Jan 5, 2020 at 15:38
  • 1
    $\begingroup$ Some years ago in the UK the number plate on a car had the following format, Letter, a number (1,2 or 3 digits) and then a three letter code. There was a debate in chemistry world's letters pages about the number of formulas or molecules you could see on number plates. HCN was one which came up. You could also have nitrosyl flouride (ONF). You can also have calcium oxide (CaO), KCN, Carbonyl sulfide COS or SCO or OCS. You can have the organometallic ligand COD (cyclooctadiene). The Solvents DMF and THF can appear also. $\endgroup$ Jan 5, 2020 at 16:51
  • 1
    $\begingroup$ More numberplate chemcials include cyanogen halides (NCI and NCF), radium oxide RaO, Barium oxide (BaO), Plutonium nitride (PuN), lithium flouride (LiF), Aluminium nitride (AlN), With the pre 1980s numberplate formate which was three letter code, number then single letter (year letter). You could have SiO2 (silica), PuO2 (plutonium dioxide). With a 1980s car you could have C60 at the start of the number plate $\endgroup$ Jan 5, 2020 at 17:01

2 Answers 2


As a creator of this memetic illustration, I feel obliged to post a brief answer.

Potassium is known for forming several metal alloys, such as a widely used Sodium-potassium alloy NaK. However, CaK doesn't exist [1]:

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.

Cited Reference
*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; #)


  1. Pelton, A. D. The Ca−K (Calcium-Potassium) System. Bulletin of Alloy Phase Diagrams 1985, 6 (1), 34–34. DOI: 10.1007/BF02871178.
  • 3
    $\begingroup$ As the creator you deserve the "accepted answer," thank you. $\endgroup$
    – user 85795
    Jan 5, 2020 at 9:05

No for a couple of reasons:

  1. Ionic bonds are between a metal and a non-metal - Ca and K are both metals.

  2. 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.

  3. Both atoms, Ca and K, aim to lose their electrons to form a full valence(thus forming cations) and have negative oxidation numbers.

  • 4
    $\begingroup$ Caesium and gold are both metals, but they easily react to form form an ionic compound, caesium auride. $\endgroup$ Jan 5, 2020 at 12:38

Not the answer you're looking for? Browse other questions tagged or ask your own question.