Strength and Stability of Acids and bases

[Javier Perez M 1H]

Hi, how do I know when an acid is strong or weak? Similarly, how do I know the stability such as leaning more to the right or left, etc?

[Sami Siddiqui 1J]

Strong acids are able to completely deprotonate, which means that all of the acid molecules can release a proton when making contact with a base in solution. Weak acids do not completely deprotonate, which means only a fraction of the molecules will actually give off protons to bases in solution. Strong bases are capable of complete protonation, meaning that all its given molecules will accept protons from an acid in solution. Following this pattern, I'm sure you can tell that weak bases do not completely protonate in a neutralization reaction. We can mostly tell if an acid or base is strong or weak by patterns listed in the lecture, but there's also a great deal of memorization involved as well. I would suggest going through the reading for Acids and Bases to get the full picture.

[Jayasree Peri 2J]

There are a few things that could make an acid stronger:
1) Atomic Radius: This only applies to a molecule with just two atoms usually. The longer the atomic radius, the stronger the acid because the interactions between the two atoms are farther apart, meaning they aren't held together as strongly. This makes it easier to take away the proton. For example, HI would be a stronger acid than HCl because the atomic radius is bigger.
2) Electronegativity: The higher the electronegativity of a certain atom, the more it pulls electrons towards it. This would make the other atoms dissociate easier because there is less pull on them. For example, HOCl is a stronger acid than HOBr because the higher electronegativity of Cl makes it easier for the H to dissociate since the charge of the O will be pulled towards the Cl.
3) Number of Os in the molecule: I'm not exactly sure what the logic behind this is (I think it's related to electronegativity), but the more Os you have in the acid, the stronger it is. For example, HClO₃ would be a stronger acid than HClO₂.
There might be more I'm forgetting, but this is a few!

[Kyle Walsh 2J]

So for weak/strong acids, there is actually a list of defined strong acids, HCl04, HBr, HI, HCl, HNO3, H2SO4, and all the rest are considered weak acids. As for stability, the stronger an acid is, the more stable it will be. Determining the relative stability of individual weak acids can be done by considering resonance, which makes an acid stronger (Ex. SO4(2-)), and the relative electronegativities of the outer atoms to the central atom (Ex. CCl3COOH is much stronger than CH3COOH because Cl has a much higher electronegativity than H), because the higher the electronegativity, the more they will pull away from the central atom, weakening the bond and strengthening the acid. Hope this helped!