OS X :: Items Properties In Powerpoint And Change The Item's Size Percentage

After migrating to Mac last year, I've also begun my migration to iWork from Office. I now have one problem that I can't seem to resolve. I am trying to paste chemical structures from Chemdraw into my slides, however each item I paste have different size. However, my chemical compounds are a specific size that I need to keep constant.Is there a way for me to alter the size of items i'd like to post by altering the percentages? In the past, I'd alter the item's properties in powerpoint and change the item's size percentage.