Although the conjunctions while and whereas have similar uses, there are some differences too. While, for example, can be used to introduce a time-clause. Whereas cannot be used to introduce a time-clause.

While

While is mainly used to introduce a time-clause. We use it when we want to talk about things that happen simultaneously.

• While she was playing, I was studying.

When both clauses have the same subject, it is possible to drop subject + be after while.

• While roaming around the city we saw many interesting sights. (= While we were roaming around the city, we saw many interesting sights.)
• While walking past the post office, I suddenly remembered that I hadn’t posted the letter. (= While I was walking past the post office, I suddenly remembered that I hadn’t posted the letter.)

While can also be used as a subordinating conjunction showing contrast. In this case, it is similar to whereas.

• While I like all kinds of music, my girlfriend only listens to western music.
• While she works three jobs in a day, her husband does nothing except watch TV.
• While I like horror movies, my girlfriend never watches them.
• I like horror movies whereas my girlfriend never watches them.
• While in India the months of July and August are relatively cool, in the US they are the hottest months in the year.
• In India the months of July and August are relatively cool, whereas in the US they are the hottest months of the year.