In a large dutch oven place the ham bone and cover with the chicken broth, it will probably not be totally immersed. Stir in the chopped onion and undrained can of tomatoes. Cover, bring to a boil and reduce heat to simmer for one hour. Remove the bone and remove all of the meat from the bone. Return the meat to the broth. Add the potatoes, celery and carrots. Simmer for 45 - 60 minutes over a very low flame. Bring to a boil, add the barley and green beans and cook for an additional 15 - 20 minutes, or until the barley is tender. Remove from heat and let sit for 10 minutes. Serve.