What does atomic number represent?

What does atomic number represent?

• A. The number of protons
• B. The number of electrons
• C. The mass number
• D. The number of neutrons

Answer: (A)

The atomic number is the number of protons in the nucleus. This count uniquely identifies the element and is what the periodic table uses to arrange elements in order. In a neutral atom, the number of electrons equals the atomic number, but the atomic number itself specifically counts protons, not neutrons or overall mass. The mass number, on the other hand, is protons plus neutrons. So neutrons can vary (creating isotopes) without changing the atomic number. For example, carbon has 6 protons, giving it atomic number 6; isotopes like carbon-12 and carbon-14 differ in neutrons but still have 6 protons and thus the same atomic number.

The atomic number is the number of protons in the nucleus. This count uniquely identifies the element and is what the periodic table uses to arrange elements in order. In a neutral atom, the number of electrons equals the atomic number, but the atomic number itself specifically counts protons, not neutrons or overall mass. The mass number, on the other hand, is protons plus neutrons. So neutrons can vary (creating isotopes) without changing the atomic number. For example, carbon has 6 protons, giving it atomic number 6; isotopes like carbon-12 and carbon-14 differ in neutrons but still have 6 protons and thus the same atomic number.