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

Answer Key - Grade 10 Science Worksheet

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

1. 1.

   A calcium ion has 20 protons and a 2+ charge. How many electrons does it have, Ari?

   18 electrons
2. 2.

   A chloride ion has 17 protons and a 1− charge. How many electrons does it have, Bo?

   18 electrons
3. 3.

   An aluminum ion has 13 protons and a 3+ charge. How many electrons does it have, Esme?

   10 electrons

4. Read this first

   Atom diagram of a fluoride ion

   9 protons and 10 neutrons in the nucleus, and 10 electrons in shells of 2 and 8. Notation: mass number 19 over atomic number 9, then F with a 1− charge.

5. 4.

   In the diagram, why is the fluoride ion's charge 1−, Jun?

   • It has one more electron than protons
   • It has one more neutron than protons
   • It lost a proton
6. 5.

   In the diagram, how many neutrons does the fluoride ion have, Kira?

   • 9
   • 10
   • 19
7. 6.

   In the diagram, why is this still fluorine, Luz?

   • It gained a proton
   • It still has 9 protons
   • It has 10 electrons in it
8. 7.

   An oxygen atom gains two electrons. What is its charge, Noah?

   • No charge
   • 2+
   • 2−
9. 8.

   When an atom becomes an ion, which particles change in number, Pia?

   • Protons
   • Electrons
   • Neutrons
10. 9.

    What do isotopes of one element share, Tala?

    • The same number of neutrons
    • The same mass number
    • The same atomic number
11. 10.

    How many neutrons does chlorine-37 (atomic number 17) have, Zee?

    • 17
    • 20
    • 37