"He talks while I read."
Translation:Il parle alors que je lis.
"alors que" is "whereas"; you can use "while" for this too, but "whereas" is unambiguous.
Alors que Sophie aime le jazz, Marie déteste ça.
Whereas Sophie loves jazz, Mary hates it.
"pendant que" is "while" in the sense where it is used for simultaneous actions.
Marc étudie la chimie pendant qu’il écoute la radio.
Marc studies chemistry while he is listening to the radio.
The thing is, in English, we can use "while" for either meaning, which confuses matters. Pendant que is the kind of "while" that refers to simultaneous events - Nero fiddled while Rome burned. Alors que is the kind of "while" that means "whereas" - Frank is a businessman, while John is an artist.
When can be used when you mean at the start of something, whereas while can be used in the process of doing something.
In these contexts they are not interchangeable:
I will be a teenager when I turn thirteen.
I will hold on to the handlebars while I am cycling.
When the exact time is unknown they can be interchangeable
(I think in French 'quand' or 'Lorsque?' could be used for the first example, 'Pendant que' would be used in the second. Could someone confirm?)
These words all have overlapping meanings.
"Lorsque" can often be used exactly as "quand" - Laura Lawless uses the example: "Je marchais lorsque tu m'as téléphoné/ Je marchais quand tu m'as téléphoné." I was walking when you called me. However, both words also have other uses, and "lorsque" can overlap with "alors que".
"Pendant que" refers to duration of time - something happening at the same time as something else. "Alors que" more often translates as "whereas" - "Frank is a businessman whereas John is an artist."
Here is some more information: http://www.frenchtoday.com/blog/linking-words-6
As I say, there is a lot of overlap, but I think you won't go far wrong if you stick to those when constructing sentences. It's just that from time to time you will see them all used in ways that don't quite conform to those definitions.
I am quite sure that someday it will all be clear to me. Yes I am.
I get that pendant que refers to the "while" of simultaneous events and not the "while" synonymous with "whereas." . But surely "while" in this sentence could mean both? He talks at the same time as I am reading. He talks whereas I read. Given that the English sentence has two meanings, DuoLingo should accept either pendant que or alors que. Stuff like this is really frustrating, especially when a perfectly acceptable translation loses you health.