Not all molecules i m sorry contain hydrogen are capable of donating protons. For example, methane (CH4) and also other hydrocarbons show no acidic properties at all. Carbon is not highly electronegative, and also so electron density is relatively evenly common in a C―H bond, and also the hydrogen atom is unlikely to depart without at the very least one electron. Also when it is external inspection to highly electronegative atoms prefer oxygen or fluorine, a hydrogen atom is not constantly strongly acidic.

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Example \(\PageIndex1\) : Proton Transfer

Acetic acid has the forecast formula

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There space a huge number of weak acids, but fortunately they loss into a few well-defined categories:

Carboxylic acids

These compounds have the basic formula RCOOH. Every react through water in the same way as acetic acid . The stamin of carboxylic mountain is dependent on the electronegative stamin of the atoms in the "R" group. Consider the compound F3COOH and H3COOH. Fluorine is the most electronegative element, when hydrogen is similar to carbon in electronegativity. Thus, the fluorines pull electron thickness away indigenous the carboxyl group. This clears electron density from the acidic oxygen-hydrogen bond, i m sorry weakens it. This weaker bond method that the hydrogen can be removed much more easily, which create a stronger acid. This ide can be used to any kind of R group. The more electronegative the R group, the more powerful the carboxylic acid will certainly be.

Weak oxyacids

These have actually the same basic formula HnXOm as strong oxyacids, yet the number of hydrogens is equal to or one much less than the number of oxygens. Because that a weak oxyacid, in various other words, m ≤ n + 1. Some examples are:


Some the the weak oxyacids, H2CO3 for example, are an extremely unstable and also cannot be separated in pure form from aqueous solution.

See more: Difference Between 1S And 2S Orbital ? Difference Between 1S And 2S Orbital

Other molecules containing acidic hydrogen atoms

Hydrogen fluoride (HF) has a very strong bond and does no donate the proton as easily as other hydrogen halides. Various other molecules in this classification are hydrogen sulfide (H2S) and hydrogen cyanide (HCN). In the last case, also though H is external inspection to C, the electronegative N atom pulls some electron density away, and the HCN molecule is a an extremely weak proton donor.

Hydrated cations

Cations, specifically those of charge +3 or much more or the the transition metals, room surrounded carefully by four to 6 water molecules in aqueous solution. An instance is Cr(H2O)63+, displayed in figure \(\PageIndex1\). The positive charge of the metal ion pulls electron thickness away native the surrounding water molecules, weakening the host of the oxygen atoms because that the hydrogen atoms. The latter deserve to consequently be much more easily donated as protons: