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: Six ( 12 % ) and 4 ( 8 % ) patients experienced grade 2 hand - foot syndrome and stomatitis , respectively ( no episodes of grade 3 ) .
### Output Text:
Six ( 12 % ) and 4 ( 8 % ) patients experienced grade 2 hand - foot syndrome and stomatitis , respectively ( no episodes of grade 3 ) . 