Atomic number is the number of protons.

Study for the IMAT Chemistry Exam. Access flashcards and multiple choice questions; hints and explanations included for each question. Prepare effectively for your exam.

Multiple Choice

Atomic number is the number of protons.

Explanation:
The atomic number is the number of protons in the nucleus. This count uniquely identifies the element, since each element has a fixed number of protons. In a neutral atom, the number of electrons equals the number of protons, but the defining property is the proton count, not the electrons. The total number of nucleons (protons plus neutrons) is the mass number and varies among isotopes, so it isn’t the atomic number. The number of neutrons alone also doesn’t determine the element.

The atomic number is the number of protons in the nucleus. This count uniquely identifies the element, since each element has a fixed number of protons. In a neutral atom, the number of electrons equals the number of protons, but the defining property is the proton count, not the electrons. The total number of nucleons (protons plus neutrons) is the mass number and varies among isotopes, so it isn’t the atomic number. The number of neutrons alone also doesn’t determine the element.

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