daltons atomic theory

the billiard ball model

Because Dalton thought atoms were the smallest particles of matter, he envisioned them as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model them. Three of his model atoms are pictured in the Figure and used to model compounds. Q: When scientists discovered smaller particles inside the atom, they realized that Daltons atomic models were too simple. How do modern atomic models differ from Daltons models? A: Modern atomic models, like the one pictured at the top of this article, usually represent subatomic particles, including electrons, protons, and neutrons.

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reintroducing the atom

Around 1800, the English chemist John Dalton brought back Democritus ancient idea of the atom. You can see a picture of Dalton 1.1. Dalton grew up in a working-class family. As an adult, he made a living by teaching and just did research in his spare time. Nonetheless, from his research he developed one of the most important theories in all of science. Based on his research results, he was able to demonstrate that atoms actually do exist, something that Democritus had only guessed.

daltons experiments

Dalton did many experiments that provided evidence for the existence of atoms. For example: He investigated pressure and other properties of gases, from which he inferred that gases must consist of tiny, individual particles that are in constant, random motion. He researched the properties of compounds, which are substances that consist of more than one element. He showed that a given compound is always comprised of the same elements in the same whole-number ratio and that different compounds consist of different elements or ratios. This can happen, Dalton reasoned, only if elements are made of separate, discrete particles that cannot be subdivided.

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atomic theory

From his research, Dalton developed a theory about atoms. Daltons atomic theory consists of three basic ideas: All substances are made of atoms. Atoms are the smallest particles of matter. They cannot be divided into smaller particles, created, or destroyed. All atoms of the same element are alike and have the same mass. Atoms of different elements are different and have different masses. Atoms join together to form compounds, and a given compound always consists of the same kinds of atoms in the same proportions. Daltons atomic theory was accepted by many scientists almost immediately. Most of it is still accepted today. However, scientists now know that atoms are not the smallest particles of matter. Atoms consist of several types of smaller particles, including protons, neutrons, and electrons.

instructional diagrams

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questions

scientists now reject most of daltons atomic theory.

a. true

-->  b. false

dalton based his ideas about atoms on his own scientific research.

-->  a. true

b. false

dalton investigated

a) pressure of gases.

b) ratios of elements in compounds.

c) protons and other subatomic particles.

-->  d) two of the above

according to daltons atomic theory

a) only compounds are made of atoms.

b) no two atoms are exactly alike.

-->  c) atoms cannot be created or destroyed.

d) all of the above

dalton thought that atoms consist of smaller particles of matter.

a. true

-->  b. false

daltons atomic theory was quickly accepted by most other scientists.

-->  a. true

b. false

dalton thought that a given compound always consists of the same kinds of atoms in the same proportions.

-->  a. true

b. false

diagram questions

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