The atomic number of an atom is:
A. The number of electrons
B. The number of neutrons
C. The number of protons
D. The number of protons plus the number of neutrons
The correct answer and explanation is:
The correct answer is C. The number of protons.
The atomic number of an atom is defined as the number of protons found in the nucleus of that atom. Protons are positively charged particles located within the nucleus, and they determine the identity of the element. Each element on the periodic table has a unique atomic number. For example, hydrogen has an atomic number of 1 because it has one proton, while carbon has an atomic number of 6 because it has six protons. The atomic number is fundamental because it defines the chemical properties of the element and its position in the periodic table.
Electrons, which are negatively charged particles, orbit the nucleus in electron shells, and their number is usually equal to the number of protons in a neutral atom to balance the overall electrical charge. However, the atomic number specifically counts only protons, not electrons. Neutrons, which are neutral particles also found in the nucleus, contribute to the atom’s mass but do not affect the atomic number. The sum of protons and neutrons is called the mass number, not the atomic number.
The distinction between atomic number and mass number is important. While the atomic number determines the element itself, the mass number determines the isotope of the element. Isotopes have the same number of protons but different numbers of neutrons. For example, carbon-12 and carbon-14 are isotopes of carbon with 6 protons each but 6 and 8 neutrons, respectively.
In summary, the atomic number is a fundamental property of atoms representing the total number of protons in the nucleus. It uniquely identifies each element and distinguishes it from all others.