How did Dmitri Mendeleev arrange the elements in his original periodic table?

• A. By alphabetical order
• B. By increasing atomic mass
• C. By chemical reactivity
• D. By increasing atomic number

Answer: (B)

Verified step by step guidance

1. Understand the historical context: Dmitri Mendeleev created the first widely recognized periodic table in the 19th century to organize known elements systematically.
2. Recognize that Mendeleev arranged elements based on a property that showed periodic trends, which was the atomic mass (now called atomic weight), not atomic number, which was discovered later.
3. Know that Mendeleev placed elements in order of increasing atomic mass, which allowed him to observe repeating patterns in chemical properties, leading to the concept of periodicity.
4. Note that Mendeleev also left gaps in his table where he predicted undiscovered elements would fit, based on the trends in atomic mass and chemical properties.
5. Conclude that the key organizing principle of Mendeleev's original periodic table was increasing atomic mass, rather than alphabetical order, chemical reactivity, or atomic number.