<https://es.coursera.org/learn/basic-chemistry#mooc>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://schema.org/Course>
<https://es.coursera.org/lecture/basic-chemistry/simple-structure-formal-charge-and-resonance-part-i-bPSdP?authMode=signup>