Two solutions:
1. Add the `/snap/bin` directory to you `$PATH`. This would give you direct access to _any_ command in that directory.
PATH=$PATH:/snap/bin
(this would go in your `~/.bashrc` file, for example).
2. Create an alias called `atom` that calls `/snap/bin/atom`. This would replace `atom` with `/snap/bin/atom` if you used the word as a command on the command line.
alias atom=/snap/bin/atom
(this could also be added to your `~/.bashrc` file).
Instead of an alias, you could have a simple shell function that does the same thing:
atom () { /snap/bin/atom "$@"; }
Changes to `~/.bashrc` would be activated when you start a new shell.