Question

4
c. aluminum-27 (atomic number = 13)

1. although electrons have mass, they are not considered in determining the mass number or atomic mass of an atom. why?

1. a hydrogen atom has one proton, two neutrons, and no electrons. is this atom neutrally charged? explain your answer.

Explanation:

1. (For question 4) The mass of an electron is approximately $\frac{1}{1836}$ the mass of a proton. This tiny mass is so insignificant that it does not meaningfully affect the total mass number or atomic mass of an atom, so it is ignored in these calculations.
2. (For question 5) A neutral atom has an equal number of positively charged protons and negatively charged electrons. This hydrogen atom has 1 positively charged proton and 0 negatively charged electrons, resulting in a net positive charge of +1, so it is not neutral. Neutrons have no charge and do not affect the overall electrical charge of the atom.

Answer:

1. (For question 4) Electrons are excluded because their mass is negligible compared to protons and neutrons.
2. (For question 5) No, the atom is not neutrally charged; it has a +1 charge.