With two questions about radium
1. what is radium position on the periodic table including a list of other elements that have similiar properties
2. five compounds that radium can form (and identify if each compound is naturally occuring, human made, or both)

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.