Why would new teachers' grade distribution consist of more As and Fs than more experienced teachers'? Three students  came to my office hours and told me that they are straight As but for some reason are failing my class. I have 14 students who got A- and A. 11 are in 80s range, 9 got 70-77, and 9 in 50-60% range (three of those didn't turn in assignments). Is this a normal grade distribution or are some failing because I am doing something wrong? I was told that the problem could be my mid-term exam (it wasn't well-designed!!!) or that I am a difficult grader.

I was also told that this grade distribution (lots of Fs!) are common for new teachers. In other words, new teachers have lots of As and lots of Fs. Honestly, I don't understand the logic behind that. How is that possible? Or why?
tl;dr: seems like perfectly acceptable distribution.  Students will try anything to get a better grade, don't mind them too much.

To begin with, with N=43, especially if this is your first time teaching the class, you don't have a lot to go on.  As you teach it a few more times, you'll get a feel for your overall grade distribution.

I personally average somewhere around 20-25% A, 40-50% B, 20-25% C, and 5-15% D/F/W across all my classes.  But I've had some individual sections that were virtually all As and Bs, and I've had one where the D/F/W was a clear majority (!).  No one in the administration complained or questioned my grading/instructional skills in that last one because they were due to extreme absences and not handing in heavily-weighted assignments, and also because I had taught it before with more "normal" (= commonly occurring, not statistically normal) distributions.  

As to new teachers having lots of As and Fs, if it fits an inverted bell curve, it's a sign that your class is probably a bit too easy, the As are people that get it, and the F are those that don't, but without more difficult questions, you have no way of discriminating any other levels.  But frankly, your distribution seems fine and unremarkable to me.

As the user autistic notes in the comments to your question, if you're concerned about too many As/Fs and not enough B/C/Ds, you may need to have questions or assignments that include both more difficult (to pull more Bs out of the As) and easier (to pull more C/Ds out of the Fs).  

Your ultimate recourse (and resource) is if the course is something that has been taught before at your university by someone who is still there, ask them to look over how you're grading.  If it seems fine to them, then you just got a class that happens to have that grade distribution.  If not, then you may want to make some minor adjustments based on their recommendation.

What I wouldn't do is judge your grading with their other instructors.  Besides the fact that they could just be very lazy students in your class alone, each department within a university will have its own culture of expectations, workloads, and grade assigning.  Those students may have As, but in a department that doesn't demand much.  You may also have students that are surprised at getting an A, if they come from one that is far more demanding.