My toddler is jealous of 4 month old?

I am a mommy of 2 little boys, my oldest son Troy is 2 and a half and VERY jealous of my 4 month old Weston. Today when I was preparing my younger sons bottle my toddler slapped him on the side of the face, enough to leave a red mark and to make his head hit back. He cried for a minute, but seems okay. Would it be too extreme to bring him to the hospital?? And also what can I do to make my toddler less jealous??!! We try to involve him in everything but he has no interest