Question

How are atomic numbers and mass numbers represented in an atom?

Answer 1

Atomic numbers and mass numbers are fundamental properties used to represent atoms.

1. Atomic Number (Z): The atomic number of an atom represents the number of protons found in the nucleus of that atom. It determines the element's identity and its position in the periodic table. In a neutral atom, the atomic number also represents the number of electrons surrounding the nucleus. For example, hydrogen has an atomic number of 1, meaning it has one proton in its nucleus.

2. Mass Number (A): The mass number of an atom represents the sum of protons and neutrons in the nucleus. It gives an approximate measure of the atom's mass. Neutrons are electrically neutral particles found in the nucleus of an atom. The number of neutrons can vary among atoms of the same element, resulting in different isotopes. Isotopes have the same atomic number but different mass numbers due to the varying number of neutrons. For example, carbon-12 has a mass number of 12, indicating it has six protons and six neutrons.

To represent an atom, you typically write the chemical symbol of the element, followed by the atomic number as a subscript, and the mass number as a superscript. For instance, the representation of a carbon-12 atom would be:

${}_6^{12}\text{C}$

Here, 6 represents the atomic number (number of protons), and 12 represents the mass number (sum of protons and neutrons). The element symbol is "C" for carbon.