Isotope
Chemistry
Level
1
How many protons, electrons, and neutrons(respectively) does the following isotope contain?
22,19,17
18,21,18
18,17,21
18,18,22
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1 solution
Argon has an atomic number of 18, so any isotope of argon contains 18 protons. Each proton contributes a 1+ charge to the charge of the atom, and each electron contributes a 1- charge. Since the isotope has no charge, we know it has the same number of electrons and protons. Therefore, the isotope has 18 electrons. The mass number is the sum of protons and neutrons in an atom or ion. Since the mass number is 40 and there are 18 protons, the ion must have 22 neutrons. The isotope contains: 18 protons 18 electrons 22 neutrons