Keybinding on F8 & F4?


I’m a beginner in using atom. I face a problem on keybinding.
I found that I can map “F4” into some function, but “F8” is not functional.

Here is the code:
‘F8’: ‘pane:show-previous-item’
‘F4’: ‘application:new-file’

F4, F5, F12 works fine, but F8, F9 are not functional.
And I solve the problem by change upper case F into lowercase f. F8 & F9 works fine.
Therefore, the code becomes:
‘f8’: ‘pane:show-previous-item’
‘f4’: ‘application:new-file’

I think it is very strange about different behavior on F4, F5, F12 keys & F8, F9 keys.
Is there any reason to regard them as different key group?

my operating system: Manjaro, gnome.