determine the mass number and the atomic number of a chlorine atom that has 17 protons and 18 neutrons.

35.453 atomic mass units

You can use Phet (Atomic masses, Elements and more)  for Chemistry

answer by yourhope:

how do models compare to real-world objects?

d. most models represent a real-world object in a simpler way.

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a polar bond is formed when electrons are shared unevenly between atoms