How can I write code/event code for ToolBar Button individually?

Nothing is wrong, you are doing it right. All the toolbar know is that you are clicking one of the buttons on it. It doesn't know which one. So on the toolBar1_ButtonClick event, it should say something like- private void toolBar1_ButtonClick(object sender, toolBarClickEventArgs e) -
What you are interested in is that 'e' there. In your code inside the event, type e and then a '.' and if you are using VS it should give you some options with intellisense.One of those options should be something along the lines of e.Button or something.
Play with it and see what you can come up with. Reply if you still can't figure it out.