Kaplan Nursing Entrance Practice Exam

The atomic number of an element is defined as what?

1. The number of neutrons

2. The total number of particles

3. The number of protons

4. The number of electrons

The correct answer is: The number of protons

The atomic number of an element is defined as the number of protons found in the nucleus of an atom of that element. This number is unique to each element and determines its identity. For example, all hydrogen atoms have an atomic number of 1, which means each hydrogen atom has one proton. The atomic number also plays a crucial role in the arrangement of elements on the periodic table, where elements are organized by increasing atomic number. In addition to defining the element, the atomic number also influences the chemical properties and reactivity of the element. Since atoms are electrically neutral, the number of electrons in a neutral atom is equal to the atomic number, but the atomic number specifically refers to protons only. This distinction helps to clarify the fundamental structure of atoms in terms of their building blocks.