Chemistry

Daltons Atomic Theory of Matter



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Modern chemistry recognizes many compounds and mixtures that result from the bonding of atoms. This basic idea is the heart around which all chemistry is structured. However, it wasn’t until the late 1700’s that these important building blocks of chemistry were discovered.

Antoine Lavoisier was the French chemist who was the first to establish an experimentally useful definition of an element. Although he had no concept of atoms, he determined that elements are substances that cannot be decomposed by any chemical reaction into simpler substances. He then realized that compounds contain definite proportions of the elements it contains. Lavoisier’s discoveries led to many other important findings that shaped the chemistry that we study today.

Lavoisier laid the experimental foundation of modern chemistry, but it wasn’t until John Dalton came around that scientists began to identify the small particles we know as atoms.

John Dalton, born in 1766, presented the results of his studies as postulates or basic statements that would define chemistry in a new way. Dalton proposed in his postulates that one: Elements are made up of tiny particles called atoms; two: All elements of a given element are identical; three: The atoms of a given element are different from those of any other element; the atoms of different elements can be distinguished from one another by their respective relative weights; four: Atoms of one element can combine with atoms of other elements to form chemical compounds; and five: Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process.

At the Time, Dalton’s postulates seemed to have uncovered more about chemistry and have a large impact on chemistry. Today, his theory still has the large impact; however, modern scientists have disproved 2 of his postulates. First of all, we know that the atoms of an element are not always identical. Atoms can exist as isotopes, which are atoms with the same number of protons and electrons, but a varying number of neutrons. Second, scientists have shown that with a tremendous amount of energy, atoms can be changed from their original state (this disproves the fifth and final postulate).

Although Dalton’s theory may not be 100% correct, his findings were quite impressive, especially when very little of the scientific resources that are available today had not yet been invented at the time. John Dalton’s original observation that evaporated water existed as an independent gas. He began to question how air and water can occupy the same space at the same time and reasoned that evaporation might be viewed as water particles mixing with water particles. After experimenting with the mixing of gases, Dalton proposed that the sizes of particles that make up different gases must be different. This hypothesis lead to further experimenting and Dalton discovered that atoms have different weights that are vitally connected to the weight relations in chemical reactions.

Over the years, decades and centuries, Dalton’s atomic theory has been tested many times and supported by recent evidence. Modern chemistry would not be what it is today if it were not for the vital discoveries made by John Dalton.

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