TeXes Science Practice Test

What did Mendeleev discover about element properties in the 1850s?

1. They varied with temperature

2. They occurred in random order

3. They repeated in regular intervals

4. They were unique to each element

The correct answer is: They repeated in regular intervals

In the 1850s, Dmitri Mendeleev made a significant contribution to chemistry with his discovery regarding the properties of elements. He observed that when elements were arranged according to increasing atomic mass, their chemical properties exhibited a periodicity; this means that certain properties of the elements repeated at regular intervals. This pattern allowed him to create the first widely recognized periodic table, leading to the understanding that similar properties recur periodically as one moves through the table. This periodic relationship provided a powerful framework for predicting the properties of unknown elements based on their positions in the table, reinforcing the idea that the behavior of elements is not haphazard but rather systematic. This insight was foundational in the development of modern chemistry, as it illustrated a deeper underlying structure in the relationships between the elements.