Count protons, neutrons and electrons in atoms, ions and isotopes

Answer Key - Grade 10 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   A sodium atom has mass number 23 and atomic number 11. How many neutrons are in its nucleus, Ari?

   12 neutrons
2. 2.

   A chlorine atom has mass number 35 and atomic number 17. How many neutrons are in its nucleus, Bo?

   18 neutrons

3. Read this first

   Atom diagram with nuclear notation

   Magnesium-24. The nucleus holds 12 protons and 12 neutrons; 12 electrons sit in shells of 2, 8 and 2. Beside it: mass number 24 written over atomic number 12, then Mg.

4. 3.

   In the diagram, why is the mass number 24, Kira?

   • 12 protons + 12 neutrons
   • 2 + 8 + 2 electrons
   • 12 protons + 12 electrons
5. 4.

   In the diagram, why does magnesium-24 have no overall charge, Luz?

   • Its 12 protons and 12 electrons balance
   • Its shells hold the charge in
   • Its neutrons cancel the protons
6. 5.

   Which particle's count decides what element an atom is, Milo?

   • Electrons
   • Neutrons
   • Protons
7. 6.

   Which particle has no charge, Noah?

   • The proton
   • The neutron
   • The electron
8. 7.

   Where are an atom's electrons, Pia?

   • Inside the protons
   • Inside the nucleus
   • Outside the nucleus
9. 8.

   In nuclear notation, what does the top number show, Ren?

   • The atomic number
   • The charge
   • The mass number
10. 9.

    In nuclear notation, what does the bottom number show, Tala?

    • The number of protons
    • The mass in grams
    • The number of neutrons
11. 10.

    What does the 14 in carbon-14 tell you, Zee?

    • Its atomic number
    • Its mass number
    • Its number of electrons