What data led to the need for change in Daltons ideas?

To understand the data that led to the need for change in Dalton's ideas, we need to look at the scientific advancements made in the late 19th and early 20th centuries. Several crucial experiments and discoveries dented Dalton's original atomic theory and paved the way for a more refined understanding of atomic structure. Here are some key data points:

1. Electrolysis: In the early 19th century, Michael Faraday's experiments on electrolysis provided evidence for the existence of electrically charged particles, which he called "ions." Faraday's work demonstrated that compounds dissolved in water conducted electricity and could be decomposed into their constituent elements. This challenged Dalton's hypothesis that atoms of different elements were indivisible.

2. Cathode Ray Tubes: In the 1880s, experiments with cathode ray tubes by scientists like Julius Plücker and Johann Wilhelm Hittorf revealed that when a high voltage was applied to a partially evacuated glass tube, rays moved from the negatively charged electrode (cathode) toward the positive electrode (anode). These rays were later identified as streams of negatively charged particles called electrons.

3. Oil Drop Experiment: In 1909, Robert Millikan performed the oil drop experiment, which accurately measured the charge of an electron. Millikan's work provided concrete evidence for the concept of discrete individual particles with specific charges, contradicting the notion of indivisible atoms proposed by Dalton.

4. Radioactivity and Nuclear Models: The discovery of radioactivity by Henri Becquerel and the subsequent research by Marie Curie, Ernest Rutherford, and Frederick Soddy found that certain elements spontaneously emitted particles and radiation. Rutherford's gold foil experiment in 1911 showed that atoms had a dense, positively charged nucleus at the center, with electrons orbiting around it in vast empty space.

These experimental findings led to the development of new models of atomic structure, such as J.J. Thomson's "plum pudding" model and, later, Rutherford's nuclear model. These models replaced Dalton's idea of indivisible atoms with a more intricate and accurate understanding of atomic composition and behavior.