Which of these compounds is more acidic:
HOCl and HOBr
According to electronegativity, it should be HOCl. But according to size, it should be HOBr...
I know the right answer is HOCl from an answer key, but I don't understand why. When do you consult atom size and when do you consult electronegativity when determining acidity?
Determining acidity involves considering multiple factors, including electronegativity and atomic size. However, when comparing the acidity between two compounds, electronegativity is generally a more important factor.
When consulting electronegativity, you are looking at the tendency of an atom to attract electrons towards itself in a chemical bond. Chlorine (Cl) has a higher electronegativity than bromine (Br), which means it has a greater ability to pull electron density towards itself. In the context of acids, a higher electronegativity typically indicates a greater ability to stabilize negative charge, making the compound more acidic. Therefore, based on electronegativity, HOCl is more acidic than HOBr.
On the other hand, atomic size can also influence acidity to some extent. As you correctly mentioned, bromine is larger than chlorine. In general, larger atoms have a more diffuse electron cloud, which makes it more difficult to stabilize negative charge. As a result, larger atoms tend to exhibit lower acidity compared to their smaller counterparts. However, the difference in atomic size between chlorine and bromine is relatively small, so in this case, electronegativity plays a more significant role in determining acidity.
To summarize, when comparing acidity between two compounds, electronegativity is usually the more important factor to consider. However, atomic size can have some influence when the difference in size is significant.