Question

Which of the following will most easily form a negative and a positive ion? Please explain.
-Sodium
-Aluminium
-Chlorine
-Helium

Answer 1

take periodic table, find electronegativities for each of those elements and the one with lowest electronegativity will most easily form positive ion and one with largest electronegativity will most easily form negative ion, you can exclude noble gasses right away.
now for as to why... you have octete rule, each of them trives to achieve full octete that means to have 8 electrons in outer shell and they can achieve that in few ways, for one they can release electrons or can take electrons to achieve that 8 electron configuration and be a happy camper
electronegativity tells you how gladly will atom take or give electron, and the higher the value the more he is selfish and wants that electron, and the lower the value the more generous that atom is and he gladly gives electron
so now knowing all that take the periodic table, read out the electronegativities and tell me who are the happy campers

Answer 2

@Kryten because Sodium has the lowest electronegativity and Chlorine has the largest electronegativity of from the 4 elements. Would that mean that Sodium forms the positive ion and Chlorine forms the negative ion?

Answer 3

yes

Answer 4

Thank you @Kryten

Answer 5

no problem

Answer 6

Al will more easily be negative. Al and Na are on the same period on the periodic table but Al(being on group iii) has more electrons in its outer shell thus the nucleus pulls its outer shell more than that of Na. Since, the Al electrons are held back more than those of Na, Na has a higher tendency to form positive ions.
But the truth is that they can't form negative ions. they are metals.