Ch.2 - Atoms, Molecules, and Ions

Problem 88b

Chapter 2, Problem 88b

The natural abundance of ³He is 0.000137%. (b) Based on the sum of the masses of their subatomic particles, which is expected to be more massive, an atom of ³He or an atom of ³H (which is also called tritium)?

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Identify the subatomic particles in each isotope: ³He has 2 protons, 1 neutron, and 2 electrons, while ³H has 1 proton, 2 neutrons, and 1 electron.

Calculate the mass of the protons in each isotope: Each proton has a mass of approximately 1.0073 amu.

Calculate the mass of the neutrons in each isotope: Each neutron has a mass of approximately 1.0087 amu.

Calculate the mass of the electrons in each isotope: Each electron has a mass of approximately 0.00055 amu.

Sum the masses of the subatomic particles for each isotope to determine which is more massive.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Subatomic Particles

Atoms are composed of subatomic particles: protons, neutrons, and electrons. Protons and neutrons reside in the nucleus and contribute to the atomic mass, while electrons are much lighter and orbit the nucleus. The number of protons defines the element, while the number of neutrons can vary, leading to different isotopes.

Isotopes

Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons. For example, both helium-3 (³He) and tritium (³H) are isotopes of hydrogen, with ³He having two protons and one neutron, while ³H has one proton and two neutrons. This difference in neutron count affects their mass and stability.

Atomic Mass Calculation

The atomic mass of an isotope is calculated based on the sum of the masses of its subatomic particles. For ³He, the mass is derived from 2 protons and 1 neutron, while for ³H, it comes from 1 proton and 2 neutrons. Understanding how to calculate and compare these masses is essential for determining which isotope is more massive.

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Related Practice

Textbook Question

Suppose a scientist repeats the Millikan oil-drop experiment but reports the charges on the drops using an unusual (and imaginary) unit called the warmomb (wa). The scientist obtains the following data for four of the drops: Droplet Calculated Charge (wa) A 3.84⨉10⁻⁸ B 4.80⨉10⁻⁸ C 2.88⨉10⁻⁸ D 8.64⨉10⁻⁸ (c) Based on your answer to part (b), how many electrons are there on each of the droplets?

Textbook Question

Suppose a scientist repeats the Millikan oil-drop experiment but reports the charges on the drops using an unusual (and imaginary) unit called the warmomb (wa). The scientist obtains the following data for four of the drops: Droplet Calculated Charge (wa) A 3.84⨉10⁻⁸ B 4.80⨉10⁻⁸ C 2.88⨉10⁻⁸ D 8.64⨉10⁻⁸ (d) What is the conversion factor between warmombs and coulombs?

Textbook Question

The natural abundance of ³He is 0.000137%. (a) How many protons, neutrons, and electrons are in an atom of ³He?

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Textbook Question

The natural abundance of ³He is 0.000137%. (c) Based on your answer to part (b), what would need to be the precision of a mass spectrometer that is able to differentiate between peaks that are due to ³He⁺ and ³H⁺?

Textbook Question

A cube of gold that is 1.00 cm on a side has a mass of 19.3 g. A single gold atom has a mass of 197.0 u. (a) How many gold atoms are in the cube?

The natural abundance of 3He is 0.000137%. (b) Based on the sum of the masses of their subatomic particles, which is expected to be more massive, an atom of 3He or an atom of 3H (which is also called tritium)?

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Key Concepts

Subatomic Particles

Isotopes

Atomic Mass Calculation

The natural abundance of ³He is 0.000137%. (b) Based on the sum of the masses of their subatomic particles, which is expected to be more massive, an atom of ³He or an atom of ³H (which is also called tritium)?