How were elements arranged in the early 1800s?

In the early 1800s, elements were arranged primarily by their physical and chemical properties and their relative atomic mass. This method reflected the understanding at the time that certain properties of elements correlate with their atomic mass. Chemists such as John Dalton and, later, Dmitri Mendeleev, contributed to this approach, emphasizing the relationship between an element's atomic mass and its behavior in chemical reactions.

This arrangement allowed scientists to identify patterns and groups of similar elements, which was crucial for the development of the periodic table. The arrangement by atomic mass laid the groundwork for subsequent refinements, such as arranging elements by atomic number, which became prevalent in the 20th century after the discovery of subatomic particles.

Using alphabetical arrangements or purely molecular weight does not provide a systematic way to classify the elements based on their inherent properties and behaviors, which is why they were not used as a primary method during that period.