Question detail
An atom of chlorine has an atomic number of 17 and a mass number of 35. How many protons, neutrons, and electrons does this atom contain?
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At a glance
Question
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Style
Topic
Atomic structure
Question
An atom of chlorine has an atomic number of 17 and a mass number of 35. How many protons, neutrons, and electrons does this atom contain?
Answer
The chlorine atom contains 17 protons, 18 neutrons, and 17 electrons.
Explanation
The atomic number indicates the number of protons, which is 17. The mass number is the sum of protons and neutrons, so the number of neutrons is calculated as mass number minus atomic number: 35 - 17 = 18. Since the atom is neutral, the number of electrons equals the number of protons, which is also 17. This question tests the understanding of atomic structure and the relationship between atomic number and mass number.
Common mistake
Misidentifying Neutrons from Mass Number
Students often subtract the atomic number from the mass number to find the number of neutrons, but then forget to adjust for the ion’s charge when calculating electrons.
Remember that the number of neutrons is always mass number minus atomic number, independent of charge. The electron count is atomic number minus the ion’s charge (negative charge means +1 electron, positive charge means –1 electron).
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