Rank the given compounds based on their relative Brønsted acidities. H-I, H-F, H-SH, H-NH2, H-CH3.
I thought it correlated with whichever element was more electronegative was also more acidic. An explanation would be much appreciated.
It correlates from left to right on the periodic table with electronegative (i.e., HF is a stronger acid than HNH2). It correlates up and down in the periodic table with size (i.e., HI is a stronger acid than HF). So CH4 should be the weakest acid and HI should be the strongest.
To rank the given compounds based on their relative Brønsted acidities, we need to consider the stability of the conjugate base formed when each compound loses a proton (H+). The stability of the conjugate base determines the acidity of the compound.
In general, factors that stabilize a conjugate base include:
1. Electronegativity: More electronegative elements stabilize negative charge better, making the conjugate base more stable.
2. Atom size: Larger atoms can accommodate negative charge better, leading to a more stable conjugate base.
3. Resonance: Compounds with resonance stabilize the negative charge over a larger area, making the conjugate base more stable.
4. Inductive effect: Electronegative atoms or groups nearby can withdraw electron density, destabilizing the conjugate base.
Based on these factors, we can rank the compounds as follows, from most acidic to least acidic:
1. H-F: Fluorine is the most electronegative element in this list, and therefore, H-F is the most acidic compound.
2. H-Cl: Chlorine is less electronegative than fluorine, but still more electronegative than the other elements in this list.
3. H-SH: Sulfur is not as electronegative as fluorine or chlorine, but it is larger in size than nitrogen and carbon, and therefore, more stable.
4. H-NH2: Nitrogen is less electronegative than sulfur and carbon, but it can still stabilize the negative charge through resonance by donating its lone pair of electrons.
5. H-CH3: Carbon is the least electronegative element in this list, so H-CH3 is the least acidic compound.
In summary, the relative Brønsted acidities of the given compounds, from most acidic to least acidic, are: H-F > H-Cl > H-SH > H-NH2 > H-CH3.
To rank the given compounds based on their relative Brønsted acidities, we need to consider the stability of the conjugate bases. A stronger acid will have a more stable conjugate base.
Your initial concept that acidity correlates with electronegativity is partially correct. Acidity does indeed increase as the electronegativity of the atom, to which the hydrogen is attached, increases. However, that is not the only factor to consider. There are other factors that affect relative acidity as well.
Let's analyze the given compounds:
1. H-I (hydrogen iodide): In this compound, hydrogen is bonded to iodine, which has high electronegativity. Therefore, it is relatively acidic.
2. H-F (hydrogen fluoride): Fluorine is the most electronegative element, so hydrogen fluoride is a stronger acid than H-I.
3. H-SH (hydrogen sulfide): Sulfur is less electronegative than fluorine and iodine, so H-SH is weaker than H-F and H-I.
4. H-NH2 (ammonia): Nitrogen is less electronegative than sulfur, so H-NH2 is weaker than H-SH but stronger than H-CH3.
5. H-CH3 (methane): Carbon is the least electronegative among these elements, making H-CH3 the weakest acid in the given compounds.
Therefore, we can rank the compounds in decreasing order of acid strength as follows:
H-F > H-I > H-SH > H-NH2 > H-CH3