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Chapter 2: Problem 10

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
In summary, Dalton's assumption that all atoms of the same element are identical in all their properties is not valid due to the discovery of isotopes. Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, resulting in variations in their atomic mass and other properties, such as chemical reactivity and radioactivity. This demonstrates that atoms of the same element can indeed have different properties, disproving Dalton's assumption.

Step by step solution

01

Introduction to Dalton's Atomic Theory

Dalton's atomic theory was proposed in the early 1800s. One of its main postulates was that all atoms of the same element are identical in every aspect, including their mass and properties. However, we now know that this assumption is not entirely accurate, mainly due to the discovery of isotopes. Let's discuss isotopes and how they show that atoms of the same element can have different properties.
02

Understanding Isotopes

Isotopes are atoms of the same element that have the same number of protons (atomic number) but different numbers of neutrons. Since they have the same number of protons, they are considered to be of the same element. However, their differing numbers of neutrons result in variations in their atomic masses and other properties. For example, carbon-12 and carbon-14 are two isotopes of the element carbon. Both have six protons, but carbon-12 has six neutrons, and carbon-14 has eight neutrons.
03

Variations in Mass

Due to the different numbers of neutrons, isotopes of the same element have different atomic masses. In the example of carbon-12 and carbon-14, carbon-12 has an atomic mass of 12 atomic mass units (amu), while carbon-14 has an atomic mass of 14 amu. This variation in mass proves that not all atoms of the same element are identical, as per Dalton's assumption.
04

Variations in Other Properties

In addition to differences in atomic mass, isotopes may also exhibit variations in other properties, such as chemical reactivity and radioactive behavior. For example, carbon-14 is radioactive, while carbon-12 is not. The difference in radioactive behavior is due to the instability caused by having more neutrons in carbon-14 compared to carbon-12.
05

Conclusion

In conclusion, Dalton's assumption that all atoms of the same element are identical in their properties is not valid. The discovery of isotopes has shown that atoms of the same element can have different numbers of neutrons, resulting in variations in atomic mass and other properties. This disproves the idea that all atoms of the same element are identical in every aspect.

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Most popular questions from this chapter

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 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?

Early tables of atomic weights (masses) were generated by measuring the mass of a substance that reacts with 1.00 g of oxygen. Given the following data and taking the atomic mass of hydrogen as 1.00, generate a table of relative atomic masses for oxygen, sodium, and magnesium. How do your values compare with those in the periodic table? How do you account for any differences?

In the periodic table, how many elements are found in each of the following? a. the halogen family b. the alkali family c. the lanthanide series

Which of the following statements is(are) correct? a. The symbols for the elements magnesium, aluminum, and xenon are Mn, Al, and Xe, respectively. b. The elements \(P,\) As, and \(B\) i are in the same family on the periodic table. c. All of the following elements are expected to gain electrons to form ions in ionic compounds: Ga, Se, and Br. d. The elements \(\mathrm{Co},\) Ni, and Hg are all transition elements. e. The correct name for \(\mathrm{TiO}_{2}\) is titanium dioxide.

Write the formula for each of the following compounds: a. chromium(III) hydroxide b. magnesium cyanide c. lead(IV) carbonate d. ammonium acetate
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