The deal announced Wednesday also includes a swap of draft picks in 2015.
The 34-year-old Cash started all 34 games last season, averaging 9.3 points, 5.6 rebounds and 2.2 assists while helping Chicago post the top record in the Eastern Conference. Heading into her 13th WNBA season, she has career averages of 12.3 points, 6.0 rebounds and 2.6 assists. She also was part of two U.S. gold medal-winning teams at the Olympics.
Clements averaged 2.2 points in 26 games as a rookie last season.
As part of the deal, Atlanta will receive the Sky's third-round selection in the 2015 draft, with Chicago getting a second-rounder from the Dream.