Mark Zuckerberg and Priscilla Chan led American philanthropists in charitable giving by a wide berth last year. According to The Chronicle of Philanthropy, Zuckerberg's donation of 18 million Facebook shares in December jumped to a total value of more than $990 million, making it the largest public gift on record for 2013.

The Chronicle lists the top 50 American philanthropists every year, and figures needed to top $37.5 million to reach the list this year. Donations from the top contributors totaled $7.7 billion — another $2.9 billion were counted as pledges — with much of the money going to non-profits in the health and science sectors. The number two spot was taken by George Mitchell of Galveston, TX, who bequeathed a $750 million grant for clean energy, natural gas sustainability, and water after his death. Google's Sergey Brin and 23andMe's Anne Wojcicki, who were ninth on the list, together donated approximately $219 million to a variety of non-profits, including the Michael J. Fox Foundation for Parkinson's Research.

The increased giving overall can be attributed to last year's stock surge, but also to a major intergenerational shift in wealth. According to the magazine, charities can expect even more big giving in 2014 as the economy improves. "It's a sure sign that the economy is getting better and people are getting a lot less cautious," Chronicle editor Stacy Palmer told the Associated Press.