When people are chatting with other people online, there is a very real sense of anonymity. Screen names, false email addresses and even fake profile pictures can make a person feel like they can do and say things they'd never do or say if they were using their real information.
However, generally speaking, people aren't truly anonymous. Federal and state law enforcement agencies have sophisticated resources to identify and track down people who do illegal things online. So while you may be able to conceal your identity from someone with whom you are chatting, you may not be able to hide from the police. With this in mind, you should understand the actions that could be considered illegal if you are chatting with a minor online.