A patient in a dentist's office is given 1.67 x 1023 molecules of dinitrogen monoxide (laughing gas), N2O (g), during a procedure. What amount in moles of
dinitrogen monoxide is the patient given?

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.