Final answer:
Elements in the same column of the periodic table share the same atomic number, which corresponds to the number of protons in the nucleus and defines the element. While the atomic number stays constant for elements within the same group, the atomic mass may vary due to different numbers of neutrons in isotopes of that element.
Step-by-step explanation:
The elements in the same column on the periodic table have the atomic number in common. The atomic number represents the number of protons in the nucleus of an atom, which is a defining characteristic of an element. The atomic number is what makes each element unique and determines the chemical properties of the element, including how it interacts with other elements during chemical reactions. Additionally, in electrically neutral atoms, the atomic number also equals the number of electrons, giving an element its characteristic chemical behavior.
Following the same logic, isotopes of an element differ in the number of neutrons they contain while retaining the same atomic number. This difference in neutron number impacts the atomic mass, or the mass number, which is the sum of protons and neutrons in an atom's nucleus. Hence, while elements in the same column share the same number of protons, they may have various numbers of neutrons, resulting in differing atomic masses for different isotopes.
The periodic table arranges elements by increasing atomic number, and elements within the same group or column share similar chemical and physical properties due to having the same number of valence electrons, which is determined by their atomic number. For any given element, its atomic mass is displayed alongside the atomic number in the periodic table; however, the atomic mass also incorporates the average of all isotopes for that element, accounting for the different numbers of neutrons.