7zip archive multiple files with their respective names

I have lots of files that I want to archive/compress using 7zip utility. They all reside in the same folder. Each archive must have the same name as the file that is to be archived. For example, if the files are 1.txt, 2.txt, 3.txt then the archives should be 1.7z, 2.7z and so on. I have found some batch scripts, but I need a bash script. I can list all the files using

for i in *.txt; do echo $i; done

but cannot make it work with 7zip command, i.e. 7z a 'archive.7z' 'file.txt'