Finding the filepath to Atom (code editor) on Ubuntu Bionic Linux for C# files

I'd like to be able to double click on C# script files in the Project pane and have them automatically open in Atom, which is a script editor for Linux. I'm using Ubuntu 18.04 (Bionic). I know how to change preferences to a text editor but I was wondering if anyone knew the filepath to externally installed packages on Ubuntu? I checked /usr/bin and it's not there. Obviously it's not in /bin (that's for system binaries only).

Thanks! n.n