Which of the following pairs of elements are likely to form an ionic compund?

helium and oxygen
magnesium and chlorine
potassium and sulfur
sodium and potassium

can you please tell me why too?

Answer:
The best way to predict whether a substance is ionic or covalent is by subracting their electronegativity values. If the result is more than 1.7, then that is ionic but below 1.7 is covalent.

You can also approximate easily by the folowing:

Metal + non-metal = ionic bonding

Nonmetal + nonmetal = covalent bonding

Metal + metal = metallic bonding


In your case: Helium + Oxygen = covalent
Magnesium + Chlorine = Ionic
Potassium + Sulfur = ionic
Sodium + Potassium = metallic
I would take magnesium and chlorine because Mg has a charge of +2 where as chlorine has a charge of -1 forming MgCl2 . A ionic compund is a compound formed between a positive charged and negative charged element due to exchange of electrons opposed to a covalent compund where it shares the electrons such as helium + oxygen
Helium is a noble gas and these don't react very easily so helium and oxygen won't form an ionic compound. Furthermore these are two non-metals.

Magnesium and chlorine will form an ionic compound. Ionic compounds are formed betweena metal and a non-metal.

Potassium and sulfur won't form an ionic compound.
These are two metals and ionic compounds are formed between a metal and a non-metal

Sodium and potassium won't form an ionic compound. Same reason as above.

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