system
Given the following post, respond as if you're commenting on Reddit:
human
Asked to meet with Dept. chair about advisor's mentoring issues

Background: I am a graduate student in a R1 university in the US. I have been having issues with my advisor, like inconsistent communication about funding, field research opportunities, and my timeline for finishing my thesis. These are admittedly serious issues, but they have all been things that I think I've been able to confront with him, though the issues haven't been resolved. From conversations with other students, I know my advisor has had other serious issues with students, such as bullying behavior like yelling at others in public and criticizing specific students in research group meetings. 

I recently received a message from my department's chair saying that she wants to meet to discuss my advisor's behavior and mentoring issues so that she can personally address it with him. I don't think her investigation started because of me, so I think another or multiple students have complained. She asked to meet with all students both individually (if they want) and as a group. I appreciate her investigation and I think that it's really important to address bullying, but I wonder whether she's the best person to make these enquiries. If she's going to personally address my advisor's mentoring issues, I worry that she might share identifying information, which is easy to do since the group is quite small. I am also worried that a group meeting might develop factions within my research group, since it seems like all students have had really unique experiences. 

So my questions are, how do I ensure that my one-on-one meeting with her is most productive? Are my personal issues with my advisor something that I should address with her? How much experience should I share regarding his treatment of my peers? How do I ensure that sharing this information is not going to impact my progress in my degree or relationship with my advisor?
gpt
OK, by your account, your adviser is giving you inconsistent information about the very things you need to successfully complete your program - your funding, your field research, and your thesis timeline. You say you've been able to confront him but also say none of the issues have been resolved, which is an indication that your confrontation has been unsuccessful thus far. You also KNOW that he's bullying other students.

You *need* the department chair to address this! Absent any information to the contrary, some is the best person, because she's the chair, and it's kind of her job. There are many doctoral student who WISH their departments would take their complaints seriously and you're in one that does. 

It seems like the chair is simply collecting information to determine how to fix this, so when you meet with her, share your concerns like you shared them here. You can tell her you're nervous about the impact this'll have on your ability to finish and successfully work with your adviser. But be honest with her about the struggles you're having, too - those are directly related to the mentoring issues she's trying to solve. If she asks or if  you think it's relevant or egregious, share what you've personally seen and witnessed your colleagues go through, but you don't have to talk about secondhand or third hand accounts.