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: RESULTS : We report seven cases where substitution of lithium , either fully or partially , with divalproex sodium was extremely helpful in reducing the cognitive , motivational , or creative deficits attributed to lithium in our bipolar patients .
### Output Text:
RESULTS : We report seven cases where substitution of <span class="chemical">lithium</span> , either fully or partially , with <span class="chemical">divalproex sodium</span> was extremely helpful in reducing the cognitive , motivational , or creative deficits attributed to <span class="chemical">lithium</span> in our bipolar patients . 