disproving+dalton

Two phenomena were being uncovered for the first time in the 1800's that would later show that atoms were not the simplest forms of matter. These were electricity and radioactivity.


 * ​Electricity**

Electricity was being studied extensively in an effort to better understand its behavior and its source. Early electrical generation was done using an [|electrostatic machine], which created an electrical potential using friction.



In 1800, Alessandro Volta made a [|voltaic pile] - alternating layers of zinc and copper - that would produce an electrical potential (a.k.a. battery).





The fact that elements like copper and zinc - which according to Dalton were composed of individual atoms - could produce electricity, meant that these atoms must have electrical 'particles' within them (recall his postulate on conservation of matter and energy as well). This was the first sign that atoms might contain a subatomic particle. Try an interactive voltaic pile here.

Radioactivity
Secondly, the discovery of radioactive elements also led to the demise of Dalton's first postulate.

In the study of a new element called uranium in 1896, [|Henri Becquerel] made an accidental discovery. Somehow, the uranium was causing unexposed photographic plates to become exposed, even in the absence of sunlight. This led to the discovery of radiation, an energy source coming from within atoms of certain elements. because these elements emitted this energy, there must be some form of subatomic structure, once again showing that atoms were not the simplest forms of matter.

[|Wilhelm Röntgen] investigated X-rays, which he generated using a Crooke's tube. He eventually used X-rays to generate images on photographic plates, which are of course used today in the medical field. He took the first medical X-ray, of his wife's hand, in 1895.



In 1899, [|Marie Curie] discovered radium, which is 2 million times more radioactive than uranium. She had also discovered polonium the year before. She would later use her knowledge to help wounded soldiers of World War I by providing mobile radiology labs and X-ray machines to help in surgically removing lead bullets or shrapnel.

The Geiger counter, a device used to detect radiation, was invented in 1911 by Hans Geiger.



In the 1920's, radioactive materials soon became a fad for curing and improving health.


 * The "Cosmos Bag" was a cotton bag containing radioactive ore, to be used as a compress on swollen or arthritic joints. It claimed to relieve pain and swelling.
 * The Revigator was a ceramic pot infused with radium, which was designed to irradiate water or other liquids for home use.


 * Radithor was radium-infused water, pre-mixed and ready to drink!
 * Up until the early 1940's, Fiestaware brand ceramics (those that were brightly colored) contained elevated amounts of radioactive uranium.

Isotopes
It was the study of atomic structure that led to the discovery of isotopes - atoms of the same element but having differing atomic masses. J. J. Thomson would be the first to identify the isotopes of neon, for example. Dalton's second postulate - that all atoms of a given element are identical - was thus shown to be incorrect.



This [|website] shows you all the possible isotopes (called nuclides) for the elements.

Here's a [|Chart of the Nuclides] at the National Nuclear Data Center (Brookhaven National Labs) web site.

Here's an [|interactive periodic table] at the NNDC.