Domanda del libro di testo
(b) Using the mass of the proton from Table 2.1 and assuming its diameter is 1.0 * 10-15 m, calculate the density of a proton in g>cm3.
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Ch.2 - Atoms, Molecules, and Ions
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232
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TOC.tableOfContents
- Ch.1 - Introduction: Matter, Energy, and Measurement177
- Ch.2 - Atoms, Molecules, and Ions231
- Ch.3 - Chemical Reactions and Reaction Stoichiometry216
- Ch.4 - Reactions in Aqueous Solution189
- Ch.5 - Thermochemistry175
- Ch.6 - Electronic Structure of Atoms168
- Ch.7 - Periodic Properties of the Elements150
- Ch.8 - Basic Concepts of Chemical Bonding177
- Ch.9 - Molecular Geometry and Bonding Theories200
- Ch.10 - Gases179
- Ch.11 - Liquids and Intermolecular Forces113
- Ch.12 - Solids and Modern Materials154
- Ch.13 - Properties of Solutions157
- Ch.14 - Chemical Kinetics199
- Ch.15 - Chemical Equilibrium128
- Ch.16 - Acid-Base Equilibria164
- Ch.17 - Additional Aspects of Aqueous Equilibria163
- Ch.18 - Chemistry of the Environment105
- Ch.19 - Chemical Thermodynamics164
- Ch.20 - Electrochemistry171
- Ch.21 - Nuclear Chemistry122
- Ch.22 - Chemistry of the Nonmetals82
- Ch.23 - Transition Metals and Coordination Chemistry79
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry16
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Non è quello che usi tu?Cambia libro di testo
Capitolo 2, Problema 91
Very small semiconductor crystals, composed of approximately 1000 to 10,000 atoms, are called quantum dots. Quantum dots made of the semiconductor CdSe are now being used in electronic reader and tablet displays because they emit light efficiently and in multiple colors, depending on dot size. The density of CdSe is 5.82 g/cm3. (b) CdSe quantum dots that are 2.5 nm in diameter emit blue light upon stimulation. Assuming that the dot is a perfect sphere and that the empty space in the dot can be neglected, calculate how many Cd atoms are in one quantum dot of this size.
Guida verificata passo dopo passo1
Calculate the volume of the quantum dot using the formula for the volume of a sphere: \(V = \frac{4}{3} \pi r^3\), where \(r\) is the radius of the sphere. Convert the diameter from nanometers to centimeters first.
Convert the volume from cubic centimeters to cubic meters if necessary, to match the units of density.
Use the density of CdSe (5.82 g/cm³) to find the mass of the quantum dot by multiplying the volume by the density.
Determine the molar mass of CdSe by adding the atomic masses of Cd and Se from the periodic table.
Calculate the number of moles of CdSe in the quantum dot by dividing the mass of the quantum dot by the molar mass of CdSe, and then use Avogadro's number to find the number of Cd atoms in the quantum dot.
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Quantum Dots
Quantum dots are nanoscale semiconductor particles that have unique optical and electronic properties due to quantum mechanics. Their size, typically ranging from 1 to 10 nanometers, allows them to emit light in specific colors when excited, which is a result of quantum confinement effects. The emission wavelength depends on the size of the dot, making them useful in applications like displays and biological imaging.
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03:22
Quantum Numbers
Volume and Density Calculations
To determine the number of atoms in a quantum dot, one must calculate its volume using the formula for the volume of a sphere (V = 4/3 π r³) and then use the density of the material to find its mass (mass = density × volume). This mass can then be converted to moles using the molar mass of the substance, allowing for the calculation of the number of atoms present in the quantum dot.
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01:56Density Concepts
Atomic Composition and Molar Mass
The atomic composition of a compound, such as CdSe, is crucial for determining the number of atoms in a given mass. Each element has a specific molar mass, which is the mass of one mole of that element. For CdSe, the molar mass can be calculated by adding the molar masses of cadmium (Cd) and selenium (Se), enabling the conversion from moles to the actual number of atoms using Avogadro's number.
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02:19Atomic Mass
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Identify the element represented by each of the following symbols and give the number of protons and neutrons in each: (a) 7433X
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Domanda del libro di testo
"The diameter of a rubidium atom is 495 pm We will consider two different ways of placing the atoms on a surface. In arrangement A, all the atoms are lined up with one another to form a square grid. Arrangement B is called a close-packed arrangement because the atoms sit in the 'depressions' formed by the previous row of atoms:
(c) If extended to three dimensions, which arrangement would lead to a greater density for Rb metal?"
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Domanda del libro di testo
"The diameter of a rubidium atom is 495 pm We will consider two different ways of placing the atoms on a surface. In arrangement A, all the atoms are lined up with one another to form a square grid. Arrangement B is called a close-packed arrangement because the atoms sit in the 'depressions' formed by the previous row of atoms:
(c) By what factor has the number of atoms on the surface increased in going to arrangement B from arrangement A?
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Domanda del libro di testo
(a) Assuming the dimensions of the nucleus and atom shown in Figure 2.10, what fraction of the volume of the atom is taken up by the nucleus?
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Domanda del libro di testo
(b) How many molecules of C13H18O2 are in this tablet?
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