code: public static  Atom centerOfMass(Atom[] points) {
  		Atom center = new AtomImpl();
  
  		float totalMass = 0.0f;
  		for (Atom a : points) {
  			float mass = a.getElement().getAtomicMass();
  			totalMass += mass;
  			center = scaleAdd(mass, a, center);
  		}
  
  		center = scaleEquals(center, 1.0f/totalMass);
  		return center;
  	}
docs: Returns the center of mass of the set of atoms. Atomic masses of the
  Atoms are used.
  
  @param points
  a set of Atoms
  @return an Atom representing the center of mass