So acidity increases across a period because the electronegativity of the conjugate base increases as move from left to right. This means it can better stabilize the negative charge. Something else that contributes to this trend is the fact that as move from left to right across a period, the bond between H and the other atom becomes more polar, allowing the bond to be broken easier (ex. HF is more polar than NH3). Is that correct? However, isn't HF a weaker acid than HI because HF is in fact a stronger bond. Doesn't this contradict the fact that HF is more polar and the bond is easier to break. Which one of the statements is right? I'm aware that the fact that I- is bigger allows the electrons to be delocalized better in the periphery and this is probably the major contributing factor to the acidity down a group but can someone please explain the electronegativity bit? Thanks.