Why are elements on the periodic table not arranged strictly by atomic mass?

• A. Because atomic mass increases in a completely regular pattern across the table.
• B. Because arranging by atomic number better reflects the periodic recurrence of chemical properties.
• C. Because atomic number does not affect the chemical properties of elements.
• D. Because atomic mass is always identical for all isotopes of an element.

Answer: (B)

Verified step by step guidance

1. Understand that the periodic table is arranged to reflect the periodic recurrence of chemical properties among elements.
2. Recognize that atomic mass does not increase in a perfectly regular pattern due to the presence of isotopes and varying neutron numbers in elements.
3. Know that atomic number, which is the number of protons in an atom's nucleus, uniquely identifies an element and directly influences its chemical behavior.
4. Realize that arranging elements by atomic number rather than atomic mass aligns elements with similar chemical properties into the same groups or columns.
5. Conclude that the periodic table is arranged by atomic number because it better represents the periodic trends and chemical properties of elements.