1. The problem statement, all variables and given/known data Which is less polarizable in each of the following groups? 1) H2CCH2 or H3CCH3 2) CH4 or C2H6 3) Na+ or Na 4) Sb3- or S2- 2. Relevant equations Polarizability is affected by the number of electrons, the distance of the electrons from the nuclear charge, and molecular orientation, although we're not considering this factor. So basically the bigger the molecule the more polarizable. 3. The attempt at a solution 1) I think it's H2CCH2 rather than H3CCH3 because the latter has more electrons attached to the carbons, and the C-H bond is non-polar. Having more electrons will only make the molecule bigger and more polarizable. This, however, is wrong according to the key, and this makes no sense, as the line of reasoning I'm using works with all the other molecules. Also the former has a double bond between its central carbons and double bonds are shorter than single bonds and that would make the former more compact than the latter. 2) CH4 is less polarizable. CH4 and the other hydrocarbon are both non-polar, but the latter is bigger, so it's easier to be distorted. Correct according to the key. 3) Cations are smaller than their respective anions and also neutral species. So Na+ is less polarizable. Size matters. Correct again. 4) Sb3- and S2- - there's no comparison. Sb is rows below S in the periodic table. S2- is way smaller than Sb3- so therefore S2- is less polarizable. Again, correct. Size matters. Is the key wrong on the first one? Or am I missing a factor here?