According to Mendeleev's periodic law, the elements were arranged in the periodic table in the order of ________.

Question

Prepp Team · Accepted Answer

Mendeleev's periodic law is a fundamental concept in the history of chemistry, explaining how elements can be organized based on their properties. Dmitri Mendeleev, a Russian chemist, made a significant contribution by proposing a periodic table that grouped elements with similar characteristics.

Understanding Mendeleev's Periodic Law

In 1869, Dmitri Mendeleev published his periodic table. His work was based on the periodic law he formulated. This law states that the physical and chemical properties of elements are a periodic function of their atomic masses.

Based on this law, Mendeleev arranged the known elements in order of increasing atomic masses. He noticed that elements with similar properties appeared at regular intervals, leading to the formation of periods (rows) and groups (columns) in his table.

Arrangement Basis in Mendeleev's Periodic Table

Let's look closely at how Mendeleev arranged the elements:

Mendeleev considered the atomic mass of each element as the primary factor for arrangement.
Elements were placed in the periodic table sequentially according to their increasing atomic masses.
He left gaps for undiscovered elements, predicting their properties based on the properties of neighboring elements in the table.
He occasionally had to place an element with a slightly higher atomic mass before an element with a slightly lower atomic mass to ensure that elements with similar properties were grouped together. This highlighted the importance of periodic properties over strict atomic mass order in some cases, but the guiding principle was atomic mass.

Analyzing the Options

Let's examine the given options in the context of Mendeleev's periodic law:

Option	Description	Relevance to Mendeleev's Law
1. Increasing atomic masses	Arranging elements from lower atomic mass to higher atomic mass.	This is exactly the basis Mendeleev used for his periodic table.
2. Decreasing atomic masses	Arranging elements from higher atomic mass to lower atomic mass.	This contradicts Mendeleev's method.
3. Decreasing atomic number	Arranging elements from higher atomic number to lower atomic number.	Atomic number was not known at Mendeleev's time. The modern periodic table uses increasing atomic number.
4. Increasing atomic number	Arranging elements from lower atomic number to higher atomic number.	This is the basis of the modern periodic table, developed much later by Moseley, not Mendeleev.

Based on the historical context and the formulation of Mendeleev's periodic law, the elements were arranged primarily in the order of increasing atomic masses.

Conclusion on Mendeleev's Arrangement

Mendeleev's periodic table was a groundbreaking achievement based on the periodic law which correlated properties with atomic masses. While there were some anomalies due to the limitations of using atomic mass, the fundamental ordering principle he used was increasing atomic mass.

Therefore, according to Mendeleev's periodic law, the elements were arranged in the periodic table in the order of increasing atomic masses.

Revision Table: Periodic Law Basis

Scientist/Table	Basis of Periodic Law/Arrangement
Mendeleev's Periodic Table	Increasing Atomic Mass
Modern Periodic Table	Increasing Atomic Number

Additional Information: Evolution of the Periodic Table

While Mendeleev's table was a major breakthrough, it had certain limitations, such as the position of isotopes and the slight discrepancy in atomic mass order for some elements (e.g., Argon and Potassium). The discovery of the atomic number by Henry Moseley in 1913 led to the modern periodic law, which states that the physical and chemical properties of elements are a periodic function of their atomic numbers. The modern periodic table arranges elements in order of increasing atomic number, which resolved many of the issues faced by Mendeleev's table.