<span>The two factors that determine whether or not a molecule is polar are if the individual bonds are even and the </span>shape<span> of the molecule. If the molecule is perfectly symmetric, the molecule will not be polar even if there are polar bonds present.</span>
Elements Y and elements Z would have similar properties due to the fact that they both posses the same number of valence electrons. They both have a single valence electron that determines the corresponding elements bonding properties and the fact that it can either donate 1 valence electron to produce an ion that would be attracted to another atom, that is also an ion. Assuming that these elements are group 1 elements, they do not undergo in covalent bonding.