Quick, think of the worst way to start a virtual chat. You might think of 'Hey', or 'Are you free?', or 'Got a sec?', or the perhaps-sinister 'We need to talk.' Not following this opening with context can induce anxiety, especially if it's between a supervisor and employee. Sometimes context is implied, if you were just corresponding with the person in a meeting. If it's out of the blue, add some context like this: "Hey, you have a sec to talk about the contract issues?" The recipient now knows what you want to talk about, and that can help them decide if they're prepared (or have time) to continue the conversation.