By making qualifying offers, Washington retains the negotiating rights to those players and has the right to match any offer sheet they might recieve from another NHL team. If any of those players were to sign an offer sheet with another team the Capitals would receive draft pick compensation.
The deadline for players to accept or decline qualifying offers is July 15, while the deadline for player-elected salary arbitration is July 5. Of those players who received qualifying offers, though, only Brouwer is eligible for arbitration.
Washington opted to not submit qualifying offers for prospects Josh Godfrey, Joe Finley and Trevor Bruess so they will become unrestricted free agents on July 1.