Lesson 2.8: l'una / le undici

I note that le una di mattina is incorrect but is contracted to l'una di mattina.  On the other hand le undici di mattina isn't contracted.

Is there a reason for this in how the two vowel clashes are viewed?

Hi Peter, 

Thanks for your question and apologies for the delay.
Hopefully this answer will be useful for other members of the community too:

“le undici di mattina” isn't contracted since “undici” is plural.
In the same way, you wouldn't say “L'undici atlete che gareggiano sono italiane" but rather “Le undici atlete che gareggiano sono italiane” (Translation: The eleven athletes who compete are Italian.)

When it comes to “una”, you could either say “è l'una” (singular) or “sono le una” (plural). You wouldn't say ”sono l'una".

Hope this helps :)