Your main problem is that there was not enough light in the scene. The settings were the same for both images but one is darker than the other. I suspect there was more lighting in the first shot because of the bright highlights visible in the eyes.
f/5.0 was wide open at 35mm or 37mm focal length so you could not open up the aperture. Your choice of 1/500 for a shutter speed means you had to use ISO 12,800 which causes the "noisy" images you see.
You could have slowed the shutter speed 2 stops to 1/125 and that would allow you to decrease the ISO 2 stops to ISO 3200. ISO 3200 would produce a much "cleaner" image but it is still not ideal.
The next step is to add more more ambient lighting or use a flash.
