One isotope of beryllium has an atomic number of 4 and a mass number
of 9. Draw a model of a beryllium atom,
labeling the protons, neutrons, and electrons.
Also label the charge on each particle.

hloride, what is the mass of calcium in

explanation:

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.