Why did the early versions of the periodic table not follow a consistent pattern?

• A. The periodic table was originally organized by alphabetical order.
• B. Elements were arranged by increasing atomic mass, which sometimes led to inconsistencies in chemical properties.
• C. Elements were grouped based solely on their physical appearance.
• D. Early scientists did not know about the existence of isotopes.

Answer: (B)

Verified step by step guidance

1. Understand that the early periodic table was primarily organized by increasing atomic mass rather than atomic number.
2. Recognize that arranging elements by atomic mass sometimes placed elements with different chemical properties next to each other, causing inconsistencies.
3. Note that the concept of atomic number (number of protons) was not known at the time, which later provided a more consistent basis for element arrangement.
4. Consider that isotopes (atoms of the same element with different masses) were unknown, which contributed to confusion when using atomic mass as the organizing principle.
5. Conclude that these factors led to early versions of the periodic table lacking a consistent pattern in chemical properties.