Install chemical-mime-data by entering the following commands in the terminal:
sudo apt update sudo apt install chemical-mime-data
chemical MIME and file type support for desktops
The chemical media type and various subtypes have been proposed by Henry Rzepa, Peter-Murray Rust and Benjamin Whitaker in 1996 as an addition to the existing MIME types. The proposal didn't succeed but various applications make use of these MIME/file types. This package adds support to Linux desktops to detect and recognize files of the chemical/* media type. . See also for http://www.ch.ic.ac.uk/chemime/.