Why exactly does increasing branching always raise the density?

[userman]

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I understand that a greater amount of mass is concentrated into a smaller space----> greater mass (perfect sense)

However, doesn't this also cause a large decrease in intermolecular interactions? Hence the reason why the boiling point decreases...



does the compacting of the molecule just create a stronger effect?

 

[Chemdude]

The change in mass due to branching is significant, while the change in volume due to weaker intermolecular interactions is very small comparatively.

 

[Hemichordate]

Umm in my Princeton Review book it definitely says that increased branching DECREASES density, as well as boiling and melting points. 😕

 

[Chemdude]

Umm in my Princeton Review book it definitely says that increased branching DECREASES density, as well as boiling and melting points. 😕

If the two compound are isomers, branching decreases density. If you have a compound and you add a hydrocarbyl group onto it, this will result in increased denisty.

 

[coyfish]

Umm in my Princeton Review book it definitely says that increased branching DECREASES density, as well as boiling and melting points. 😕

Depends on the context and the molecule. BP and MP are USUALLY but not always correlated. Just from memory some symmetrical molecules with branching actually increases MP. Because it allows them to form better crystals. Perhaps that is why it could increase density? Anyway that is what I recall from my Kaplan review books.