Lesson 2 Matter
Dalton's Atomic Theory
“It’s the right idea, but not the right time.” –John Dalton
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B2.8 John Dalton
B2.8 John Dalton
An analogy that can be used to help you visualize Dalton’s model of the atom is a solid sphere like a billiard ball.
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B2.9: Dalton’s atom
B2.9: Dalton’s atom
Around 1804, English chemist John Dalton resurrected Democritus’s idea of the atom. While investigating properties of gases and observing how chemicals reacted and recombined, he inferred that matter must contain tiny, individual particles that
are in constant, random motion.
In addition to scientific observation, Dalton also used two known laws to help develop his theory: the law of conservation of mass and the law of constant composition.
His theory became widely accepted because it could be used to explain many previously unexplainable observations.
Even though his theory is over 200 years old and some of his theory has been disproved, many of his points are still valid.
In addition to scientific observation, Dalton also used two known laws to help develop his theory: the law of conservation of mass and the law of constant composition.
The five main points of Dalton’s atomic theory are as follows:
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All matter is made of atoms that are indivisible and indestructible.
- All atoms of a given element are identical in mass and properties.
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Atoms of different elements have different masses and properties.
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Compounds are formed by a combination of two or more different kinds of atoms and always in the same ratio.
- Atoms are not destroyed during a chemical reaction; rather they are rearranged.
His theory became widely accepted because it could be used to explain many previously unexplainable observations.
Even though his theory is over 200 years old and some of his theory has been disproved, many of his points are still valid.
Did You Know?
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B2.10 Dalton’s symbols for different elements
B2.10 Dalton’s symbols for different elements
Dalton was the first to use standard symbols for elements. These symbols are quite different from the element symbols on the modern periodic table!
Read This
Please read page 22 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on John Dalton’s atomic theory. Remember, if
you have any questions or you do not understand something, ask your teacher! Practice Questions
Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses
(where necessary) to study from.
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The contribution John Dalton made to atomic theory was his discovery that
- every atom was positively charged
- every element consisted of one type of atom
- atoms had nuclei
- atoms could be divided into smaller parts
- True or False: Dalton thought that atoms were made up of smaller particles.
False. Dalton thought that atoms were the smallest particles that could not be subdivided farther.
- Write the five points of Dalton’s atomic theory in your own words. This means that you cannot copy the points down; you must use words that make sense to you.