How do I know if covalent compounds are polar bond by only seeing their chemical formula?

if the compound is made of just two elements, if one is a metal (ie belongs to any of groups 1, 2 or 3) and the other element a non metal, (ie belongs to group 5, 6 or 7) then the compound is most likely to be an ionic compound. For example NaCl, MgOIf the compound is made of identical non metalic elements as in O2, Cl2 then the compound is covalentIf the compoud is made of just two elements that are both non metals such as in SO2, CO, NO, CCl4, the compound is covalentIf the compound is made up of more than two elements, such as in HNO3, Na2CO3, CuSO4.5H2O, you may need to break the compound into dissociating parts. You will see that, the compounds are ionic.Hydrocarbons, compounds containing only hydrogen and carbon of varying molecular size are all covalent. Examples are C2H6, C2H4, C2H2

Note that there could be some little exceptions to the examples given. Mostly with first members of every group because of their small size which make them show substantial deviations from group behavior. For example HCl is covalent not ionic.

the catch is that the top numbers are atomic masses the bottom numbers are the numbers of protons and electrons in an uncharged atom. they are the number of that atoms as you would find them on the periodic table. further, the numbers on the left are used to determine the missing numbers on the right

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer

The answer to this problem is. 67