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: Previous clinical studies have proposed that risperidone ' s pharmacologic profile may produce improved efficacy for negative psychotic symptoms and decreased propensity for extrapyramidal side effects ; features shared by so - called ' atypical ' neuroleptics .
### Output Text:
Previous clinical studies have proposed that <span class="chemical">risperidone</span> ' s pharmacologic profile may produce improved efficacy for negative psychotic symptoms and decreased propensity for extrapyramidal side effects ; features shared by so - called ' atypical ' neuroleptics . 