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Moseley established the concept of atomic number by studying X-rays emitted by the elements. The X-rays emitted by some of the elements have the following wavelengths: $$ \begin{array}{ll} \hline \text { Element } & \text { Wavelength }(\AA) \\\ \hline \mathrm{Ne} & 14.610 \\ \mathrm{Ca} & 3.358 \\ \mathrm{Zn} & 1.435 \\\ \mathrm{Zr} & 0.786 \\ \mathrm{Sn} & 0.491 \\ \hline \end{array} $$

Short Answer

Expert verified
The relationship between the X-ray wavelengths and atomic numbers for the given elements can be represented by the equation: \( A = \frac{k}{Z^2} \), where A is the X-ray wavelength, Z is the atomic number, and k is an approximately constant value.

Step by step solution

01

Write down the given information with the elements' atomic numbers

We have the following information about the elements and their emitted X-ray wavelengths: Element | Atomic Number (Z) | Wavelength (A) (in Ã…) --- | --- | --- Ne | 10 | 14.610 Ca | 20 | 3.358 Zn | 30 | 1.435 Zr | 40 | 0.786 Sn | 50 | 0.491
02

Study the relationship between the atomic number (Z) and the X-ray wavelengths

To find a pattern between the atomic numbers and the X-ray wavelengths, we can try plotting the wavelength (A) versus atomic number (Z) in a graph and look for a mathematical relationship between them. Remember that we are trying to find a relationship that Moseley established while studying these X-rays.
03

Find a mathematical relationship between the atomic number (Z) and the X-ray wavelengths

If we plot the values, it seems that the X-ray wavelength is inversely proportional to the square of the atomic number (Z) for these elements. We can now try to fit the data to some formula and see if we get an equation that relates these quantities. Let's denote the relationship as: \( A = \frac{k}{Z^2} \) Where: - A is the X-ray wavelength - Z is the atomic number - k is a constant
04

Calculate and verify the constant 'k' for each element

Now, we can calculate the constant 'k' for each element using the formula above and see if its value is consistent for all the elements. Element | Atomic Number (Z) | Wavelength (A) | k (Z^2 * A) --- | --- | --- | --- Ne | 10 | 14.610 | 1461 Ca | 20 | 3.358 | 1343 Zn | 30 | 1.435 | 1289 Zr | 40 | 0.786 | 1256 Sn | 50 | 0.491 | 1227 The values of the constant 'k' are very close to each other, suggesting that Moseley was able to establish the concept of atomic number by studying the X-ray wavelengths and finding a connection between them and the atomic numbers. This relationship can be represented as: \( A = \frac{k}{Z^2} \)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Atomic Number
The concept of atomic number, often denoted as 'Z', is fundamental in understanding the properties of elements and their place in the periodic table. It represents the number of protons in an atom's nucleus, which is unique for each element. It directly determines the element's identity and influences its chemical behavior. For example, Neon (Ne) has an atomic number of 10, indicating it has 10 protons in its nucleus.

From the exercise, when examining the atomic numbers of different elements like Calcium (Ca), Zinc (Zn), Zirconium (Zr), and Tin (Sn), we see that these numbers increase stepwise. Moseley used the atomic number as a pivotal part of his law to establish a firm connection between this numerical identifier of elements and the characteristics of the X-rays they emit.
X-ray Wavelengths
The term X-ray wavelengths describes the distance between successive peaks of an X-ray wave. X-rays themselves are a type of electromagnetic radiation, much like visible light, but with a much shorter wavelength. This characteristic enables them to penetrate substances that light cannot. In the provided exercise, we are given the wavelengths of X-rays emitted by various elements, such as Neon (Ne) at 14.610 Angstroms (Ã…) and Tin (Sn) at 0.491 Ã….

Understanding these wavelengths is critical as they are indicative of the energy levels of electrons within atoms and can be used to identify elements, as per the work of Moseley. The analysis of how X-ray wavelengths vary with atomic numbers leads to insights into the atomic structure and the behavior of electrons within the atom.
Atomic Number and X-ray Relationship
Delving into the relationship between atomic number and X-ray wavelengths, Moseley discovered that there was a predictable pattern to the X-rays emitted by atoms when their inner-shell electrons are excited. This relationship turned out to be key to the development of modern atomic theory. As seen in the exercise, when the atomic numbers scale upwards, the corresponding X-ray wavelengths become shorter. This suggests a specific mathematical relationship between these two variables, which Moseley defined and which we often refer to as Moseley's law.

The investigation into this relationship showcased Moseley's ingenuity in linking a physical property (X-ray wavelength) to a fundamental atomic characteristic (atomic number), thereby allowing for the atomic number to be more precisely determined.
Inversely Proportional Relationship
In an inversely proportional relationship, as one variable increases, the other decreases at a rate that keeps their product constant. Moseley's law hinges on this kind of relationship between the atomic number and the X-ray wavelengths. Our exercise illustrates this through the equation
\[ A = \frac{k}{Z^2} \]
which implies that the wavelength 'A' is inversely proportional to the square of the atomic number 'Z'. The process of plotting the provided values and calculating a consistent 'k' across several elements, as presented in the exercise, reinforces this inverse proportionality. As an educational concept, understanding inverse relationships is crucial in physics and other scientific disciplines, as it describes how quantities counterbalance each other. This concept in X-ray spectroscopy also demonstrates how advancing our understanding of elements' properties often requires a deep dive into the mathematical relationships governing their behavior.

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Most popular questions from this chapter

For each of the following pairs, indicate which element has the smaller first ionization energy: (a) \(\mathrm{Ti}, \mathrm{Ba} ;(\mathrm{b}) \mathrm{Ag}, \mathrm{Cu} ;(\mathrm{c}) \mathrm{Ge}\) \(\mathrm{Cl} ;\) (d) \(\mathrm{Pb},\) Sb. (In each case use electron configuration and effective nuclear charge to explain your answer.)

The interior of the planets Jupiter and Saturn are believed to contain metallic hydrogen: hydrogen that is put under such tremendous pressure that it no longer exists as \(\mathrm{H}_{2}\), molecules, but instead exists as an extended metallic solid. Predict what properties metallic hydrogen might have compared to "normal" hydrogen in terms of first ionization energy, atomic size, and reactivity.

When magnesium metal is burned in air (Figure 3.6 ), two products are produced. One is magnesium oxide, \(\mathrm{MgO}\). The other is the product of the reaction of \(\mathrm{Mg}\) with molecular nitrogen, magnesium nitride. When water is added to magnesium nitride, it reacts to form magnesium oxide and ammonia gas. (a) Based on the charge of the nitride ion (Table 2.5 ), predict the formula of magnesium nitride. (b) Write a balanced equation for the reaction of magnesium nitride with water. What is the driving force for this reaction? (c) In an experiment a piece of magnesium ribbon is burned in air in a crucible. The mass of the mixture of \(\mathrm{MgO}\) and magnesium nitride after burning is \(0.470 \mathrm{~g}\). Water is added to the crucible, further reaction occurs, and the crucible is heated to dryness until the final product is \(0.486 \mathrm{~g}\) of \(\mathrm{MgO}\). What was the mass percentage of magnesium nitride in the mixture obtained after the initial burning? (d) Magnesium nitride can also be formed by reaction of the metal with ammonia at high temperature. Write a balanced equation for this reaction. If a 6.3 -g Mg ribbon reacts with \(2.57 \mathrm{~g} \mathrm{NH}_{3}(g)\) and the reaction goes to completion, which component is the limiting reactant? What mass of \(\mathrm{H}_{2}(g)\) is formed in the reaction? (e) The standard enthalpy of formation of solid magnesium nitride is \(-461.08 \mathrm{~kJ} / \mathrm{mol} .\) Calculate the standard enthalpy change for the reaction between magnesium metal and ammonia gas.

Write a balanced equation for the reaction that occurs in each of the following cases: (a) Potassium metal burns in an atmosphere of chlorine gas. (b) Strontium oxide is added to water. (c) A fresh surface of lithium metal is exposed to oxygen gas. (d) Sodium metal is reacted with molten sulfur.

One way to measure ionization energies is ultraviolet photoelectron spectroscopy (UPS, or just PES), a technique based on the photoelectric effect. coo (Section 6.2 ) In PES, monochromatic light is directed onto a sample, causing electrons to be emitted. The kinetic energy of the emitted electrons is measured. The difference between the energy of the photons and the kinetic energy of the electrons corresponds to the energy needed to remove the electrons (that is, the ionization energy). Suppose that a PES experiment is performed in which mercury vapor is irradiated with ultraviolet light of wavelength \(58.4 \mathrm{nm}\). (a) What is the energy of a photon of this light in eV? (b) Write an equation that shows the process corresponding to the first ionization energy of \(\mathrm{Hg}\). (c) The kinetic energy of the emitted electrons is measured to be \(10.75 \mathrm{eV}\). What is the first ionization energy of Hg in kJ/mol? (d) Using Figure 7.9 , determine which of the halogen elements has a first ionization energy closest to that of mercury.

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