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Ch.21 - Nuclear Chemistry
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.21 - Nuclear ChemistryProblem 20b
Chapter 21, Problem 20b

Each of the following nuclei undergoes either beta decay or positron emission. Predict the type of emission for each: (b) 8938Sr.

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Step 1: Understand the concept of beta decay and positron emission. Beta decay is a type of radioactive decay where a beta particle (an electron or a positron) is emitted. In beta-minus decay, a neutron is converted into a proton and an electron, which is then emitted. In beta-plus decay or positron emission, a proton is converted into a neutron and a positron, which is then emitted.
Step 2: Identify the atomic number and mass number of the given isotope. For 8938Sr, the atomic number is 38 and the mass number is 89.
Step 3: Check the neutron to proton ratio. If the ratio is high, the nucleus is unstable and will undergo beta decay to increase the number of protons and decrease the number of neutrons, thus lowering the ratio. If the ratio is low, the nucleus will undergo positron emission to increase the number of neutrons and decrease the number of protons, thus increasing the ratio.
Step 4: Calculate the number of neutrons in the nucleus by subtracting the atomic number from the mass number. For 8938Sr, the number of neutrons is 89 - 38 = 51.
Step 5: Compare the neutron to proton ratio with those of stable isotopes. If the ratio is higher than those of stable isotopes, the nucleus will undergo beta decay. If the ratio is lower, the nucleus will undergo positron emission. For 8938Sr, the neutron to proton ratio is 51/38, which is higher than the stable ratio for lighter elements (around 1), so it will undergo beta decay.

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Key Concepts

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

Beta Decay

Beta decay is a type of radioactive decay in which a nucleus emits a beta particle, which is an electron or a positron. In beta minus decay, a neutron is converted into a proton, increasing the atomic number by one, while in beta plus decay (positron emission), a proton is converted into a neutron, decreasing the atomic number by one. This process helps the nucleus achieve a more stable configuration.
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Positron Emission

Positron emission, also known as beta plus decay, occurs when a proton in the nucleus is transformed into a neutron, resulting in the emission of a positron (the antimatter counterpart of an electron). This process decreases the atomic number of the element by one, leading to the formation of a different element. Positron emission is common in isotopes that are proton-rich and seek stability.
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Nuclear Stability and the Band of Stability

The band of stability is a region on a graph of neutron number versus proton number where stable nuclei are found. Nuclei outside this band are unstable and tend to undergo radioactive decay to achieve stability. The type of decay (beta decay or positron emission) depends on the ratio of neutrons to protons; if a nucleus has too many protons, it may undergo positron emission, while too many neutrons may lead to beta decay.
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Related Practice
Textbook Question

Predict the type of radioactive decay process for the following radionuclides: (c) phosphorus-32. (d) chlorine-39.

Textbook Question

Despite the similarities in the chemical reactivity of elements in the lanthanide series, their abundances in Earth's crust vary by two orders of magnitude. This graph shows the relative abundance as a function of atomic number. Which of the following statements best explains the sawtooth variation across the series? (a) The elements with an odd atomic number lie above the belt of stability. (b) The elements with an odd atomic number lie below the belt of stability. (c) The elements with an even atomic number have a magic number of protons. (d) Pairs of protons have a special stability.

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Textbook Question

Each of the following nuclei undergoes either beta decay or positron emission. Predict the type of emission for each: (a) tritium, 31H.

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Textbook Question

Predict the type of radioactive decay process for the following radionuclides: (b) 6829Cu.

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