angularjs element manipulation

Question

I am confused about angularjs manipulation.

How come:

   angular.element("#elementID").is(':visible') ;   // works
   angular.element("#elementID").slideUp() ;   // works
   angular.element("#elementID").style.opacity = 1 ; // **doesn't work**

   angular.element("#elementID")[0].style.opacity = 1 ;   // works
   angular.element("#elementID").css('opacity' : 1) ;   // **doesn't work**

I have a Cordova/Ionic app, jquery is installed. I feel the .css(field : value) should be working.

The various methods keep tripping me up. Can someone shed some light on this for me?