Arrangement of Elements by Mendeleev and Meyer:

Introduction:
Dmitri Mendeleev and Lothar Meyer were two prominent chemists who independently proposed the arrangement of elements in the periodic table. Their work laid the foundation for the modern periodic table we use today. Both Mendeleev and Meyer recognized the need for a systematic organization of elements to better understand their properties and relationships.

Proposal:
Mendeleev and Meyer both proposed arranging the elements in increasing order of their atomic weights. This means that the elements with the lowest atomic weights would be placed first, followed by those with higher atomic weights. This arrangement allowed for similarities and trends in properties to be observed.

Reasoning:
1. Increasing Order of Atomic Weights: The main reason for arranging elements in increasing order of atomic weights is that it reflects the periodicity of elemental properties. Mendeleev and Meyer noticed that properties of elements repeated at regular intervals when they were arranged in this manner.

2. Similarities in Properties: When elements are arranged in increasing order of atomic weights, elements with similar properties tend to fall into the same vertical columns or groups. This observation led to the identification of various periodic trends, such as the gradual change in atomic size, reactivity, and chemical behavior.

3. Prediction of Missing Elements: One of the significant achievements of Mendeleev's periodic table was the prediction of the existence and properties of yet-to-be-discovered elements. By leaving gaps in the table for missing elements, Mendeleev accurately predicted the properties of these elements based on the trends observed in other elements within the same group.

4. Revised by Atomic Numbers: While Mendeleev and Meyer initially arranged elements by atomic weights, this order was later revised with the discovery of atomic numbers. It was found that arranging elements by increasing order of atomic numbers provided a more accurate representation of the periodic trends and similarities in properties.

Conclusion:
In conclusion, Mendeleev and Meyer proposed the arrangement of elements in increasing order of their atomic weights. This arrangement allowed for the observation of periodic trends and similarities in properties. Although the periodic table is now arranged based on atomic numbers, the initial proposal by Mendeleev and Meyer laid the groundwork for our understanding of the periodic table and its significance in chemistry.