For each of the following pairs of compounds, predict which...

For each of the following pairs of compounds, predict which would exhibit hydrogen bonding. Justify your prediction. It may help to write a Lewis formula for each. (a) ammonia, $\mathrm{NH}_{3}$, or phosphine, $\mathrm{PH}_{3} ;$ (b) ethylene, $\mathrm{C}_{2} \mathrm{H}_{4},$ or hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4} ;$ (c) hydrogen fluoride, $\mathrm{HF}$, or hydrogen chloride, HCl.

Key Concepts

Intermolecular Forces

Intermolecular forces refer to the forces that mediate interaction between molecules, including hydrogen bonds, dipole-dipole interactions, and London dispersion forces. The presence and strength of these forces are crucial for understanding the behavior, such as boiling points and solubility, of different compounds.

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms as well as the lone pairs of electrons in a molecule. These diagrams assist in identifying the presence of lone pairs and determining molecular geometries, both of which are critical for assessing whether hydrogen bonding is possible.

Hydrogen Bonding

Hydrogen bonding is a strong type of intermolecular force that occurs when a hydrogen atom covalently bonded to a highly electronegative atom (typically nitrogen, oxygen, or fluorine) is attracted to a lone pair on a neighboring electronegative atom. This interaction significantly influences the physical and chemical properties of substances.

Electronegativity

Electronegativity is the measure of an atom's ability to attract electrons in a chemical bond. Atoms with high electronegativity, such as nitrogen, oxygen, and fluorine, when bonded to hydrogen, create polarized bonds that facilitate hydrogen bonding because of the substantial partial positive charge on hydrogen.

Transcript

00:01 This question is asking about hydrogen bonding for us to determine which molecules or substances have hydrogen bonding.

00:09 So remember, before we answer this question, we have to appreciate that for hydrogen bonding, hydrogen bonding, two conditions must be met.

00:22 Number one, there should be a hydrogen atom that is bonded or attracted to a highly electro -negative, atom in another molecule.

00:42 So for us to justify or to conclude that there is hydrogen bonding, there should be a hydrogen atom that is bonded to an electron negative atom.

00:54 And when we are talking about highly electron negative atoms, are talking about oxygen, fluorine, and nitrogen.

00:59 So if a substance has hydrogen and any of these atoms or elements then we can conclude to say there is hydrogen bonding or hydrogen bonding exists in that substance so looking at the first set we've got nh3 and ph 3 if we are to draw these we've got nh3 and h3 and h3 and p and n these are all in group 5 so when they bond with 3 there's got a long there is a loan pair of electrons that is left the same applies for ph 3 h and h but here we'll say hydrogen bonding only exists in nh3 because we have got a hydrogen atom that is bonded to a highly electronegative atom phosphorus is not highly electronegative so we can't talk about hydrogen bonding in here so applying the same principle to the next set we have c2h4 and hydrazine n2h4 if we are to draw this this is our c2h4 then for hydrazin we have n then we have h h but we also have low pairs of electrons here.

02:55 If we notice here we've got hydrogen in both but the hydrogen atoms in ethylene are not bonded to a highly electronegative atom or element...

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