In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: One patient in the Gamma Knife group ( 3 . 4 % ) developed a homonymous hemianopsia 9 months following treatment and 5 patients ( 27 . 7 % ) in the radiofrequency group became transiently confused postoperatively .
### Output Text:
One patient in the Gamma Knife group ( 3 . 4 % ) developed a homonymous hemianopsia 9 months following treatment and 5 patients ( 27 . 7 % ) in the radiofrequency group became transiently confused postoperatively . 