X and Y have atomic numbers 16 and 12 respectively. Write the formula of a compound formed by X and Y.
X-->2,8,2
Y-->2,8,6
X belongs to 3rd period - 2nd group.
So the element is Mg
Y belongs to 3rd period - 6th group.
So the element is Sulphur.
{no. of electrons in the outer most shell determines the group and total no.of shells determine the period.}
They form ionic bonds because they complete their octet by transfring electrons.
therefore they exist in the form of XY by completing their octet (ionic bond).