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Chapter 2: Problem 9

Dalton assumed that all atoms of the same element were identical in all their properties. Explain why this assumption is not valid.

Short Answer

Expert verified
Dalton's assumption that all atoms of the same element are identical in all their properties is not valid due to the existence of isotopes. Isotopes have the same number of protons but different numbers of neutrons, leading to differences in atomic mass and some physical properties like boiling and melting points. Additionally, some chemical reactions may exhibit slight differences called "isotope effect."

Step by step solution

01

Identify the assumption

Dalton assumed that all atoms of a specific element are identical in all their properties. This assumption was made in an early stage of atomic theory development, but it has been proven to not be entirely correct.
02

Introduce isotopes

It is essential to understand isotopes to explain why Dalton's assumption is not valid. Isotopes are atoms of the same element (i.e. the same number of protons) but with a different number of neutrons. This difference in neutrons results in a varying atomic mass for the isotopes of the same element.
03

Examples of elements with isotopes

Common examples of elements with isotopes are hydrogen, carbon, and oxygen. Hydrogen has three isotopes: protium (one proton, zero neutrons), deuterium (one proton, one neutron), and tritium (one proton, two neutrons). These hydrogen isotopes have different atomic masses due to the different number of neutrons.
04

Differences in physical properties of isotopes

The varying amount of neutrons in isotopes also leads to differences in some physical properties such as mass, boiling point, and melting point. For example, the deuterium isotope of hydrogen has a higher boiling and melting point compared to protium.
05

Differences in chemical properties of isotopes

Although the chemical properties of isotopes are generally similar because they have the same number of protons and electrons, some chemical reactions may exhibit small differences called "isotope effect." This can happen when the rate of a reaction depends on the mass of the reacting isotopes.
06

Conclusion

Dalton's assumption that all atoms of the same element are identical in all their properties is not valid because of the existence of isotopes. Isotopes of the same element have different numbers of neutrons, leading to differences in mass, as well as variation in some physical properties and, in some cases, chemical properties.

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Most popular questions from this chapter

Name the compounds in parts a-d and write the formulas for the compounds in parts e-h. a. NaBr b. \(\mathrm{Rb}_{2} \mathrm{O}\) c. \(\mathrm{CaS}\) d. AII \(_{3}\) e. strontium fluoride f. aluminum selenide g. potassium nitride h. magnesium phosphide

a. List the noble gas elements. Which of the noble gases has only radioactive isotopes? (This situation is indicated on most periodic tables by parentheses around the mass of the element. See inside front cover.) b. Which lanthanide element has only radioactive isotopes?

Section \(2.3\) describes the postulates of Dalton's atomic theory. With some modifications, these postulates hold up very well regarding how we view elements, compounds, and chemical reactions today. Answer the following questions concerning Dalton's atomic theory and the modifications made today. a. The atom can be broken down into smaller parts. What are the smaller parts? b. How are atoms of hydrogen identical to each other, and how can they be different from each other? c. How are atoms of hydrogen different from atoms of helium? How can \(\mathrm{H}\) atoms be similar to He atoms? d. How is water different from hydrogen peroxide \(\left(\mathrm{H}_{2} \mathrm{O}_{2}\right)\) even though both compounds are composed of only hydrogen and oxygen? e. What happens in a chemical reaction, and why is mass conserved in a chemical reaction?

Would you expect each of the following atoms to gain or lose electrons when forming ions? What ion is the most likely in each case? a. \(\mathrm{Ra}\) b. In c. \(\mathrm{P}\) d. Te e. Bi f. Rb

Which of the following explain how an ion is formed? Explain your answer. a. adding or subtracting protons to/from an atom b. adding or subtracting neutrons to/from an atom c. adding or subtracting electrons to/from an atom
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