We all know that it's better to send a query letter for an article, than the finished article itself, because editors like to have input into how an article is written. So don't be expecting a check by return mail, expect the editor to read your query, like your idea, then call and make you an offer instead.
When an editor calls, be professional on the phone. Don't forget to ask the pay rate, if expenses are covered, and whether there will be a "kill" fee. Sometimes editors will ask untried or unknown writers to do articles "on spec."
That means you do the work and if they like it they'll pay you. It's a good way to break in the articles market, and it's a good way for an editor to assign something to an unknown writer without losing either money or face.
In the beginning you may okay this, but when you have considerable publishing credits, the proper thing to do when an editor says "on spec," is to say, "I'd really like to work with you, but I do have other commitments and I can't devote that much time without some insurance. What about a kill fee?" The kill fee is what you're paid for your time, if they hate the article and decide not to use it after you've done all the work on speculation.