# Define radioactive dating in chemistry

Following the somewhat serendipitous discovery of radioactivity by Becquerel, many prominent scientists began to investigate this new, intriguing phenomenon. During the beginning of the twentieth century, many radioactive substances were discovered, the properties of radiation were investigated and quantified, and a solid understanding of radiation and nuclear decay was developed. The spontaneous change of an unstable nuclide into another is radioactive decay. The unstable nuclide is called the parent nuclide ; the nuclide that results from the decay is known as the daughter nuclide. The daughter nuclide may be stable, or it may decay itself. The radiation produced during radioactive decay is such that the daughter nuclide lies closer to the band of stability than the parent nuclide, so the location of a nuclide relative to the band of stability can serve as a guide to the kind of decay it will undergo Figure 1.

## 20.6: The Kinetics of Radioactive Decay and Radiometric Dating

Another approach to describing reaction rates is based on the time required for the concentration of a reactant to decrease to one-half its initial value. If two reactions have the same order, the faster reaction will have a shorter half-life, and the slower reaction will have a longer half-life. The half-life of a first-order reaction under a given set of reaction conditions is a constant.

This is not true for zeroth- and second-order reactions. The half-life of a first-order reaction is independent of the concentration of the reactants. This becomes evident when we rearrange the integrated rate law for a first-order reaction Equation This plot shows the concentration of the reactant in a first-order reaction as a function of time and identifies a series of half-lives, intervals in which the reactant concentration decreases by a factor of 2.

In a first-order reaction, every half-life is the same length of time. If we know the rate constant for a first-order reaction, then we can use half-lives to predict how much time is needed for the reaction to reach a certain percent completion. For a first-order reaction, the concentration of the reactant decreases by a constant with each half-life and is independent of [A]. The anticancer drug cis-platin hydrolyzes in water with a rate constant of 1.

Calculate the half-life for the hydrolysis reaction under these conditions. If a freshly prepared solution of cis-platin has a concentration of 0. What is the percent completion of the reaction after 5 half-lives? Asked for: B After 5 half-lives about 38 h , the remaining concentration of cis-platin will be as follows:.

After 10 half-lives 77 h , the remaining concentration of cis-platin will be as follows:. C The percent completion after 5 half-lives will be as follows:. Ethyl chloride decomposes to ethylene and HCl in a first-order reaction that has a rate constant of 1. Radioactivity, or radioactive decay, is the emission of a particle or a photon that results from the spontaneous decomposition of the unstable nucleus of an atom.

The rate of radioactive decay is an intrinsic property of each radioactive isotope that is independent of the chemical and physical form of the radioactive isotope. The rate is also independent of temperature. In this section, we will describe radioactive decay rates and how half-lives can be used to monitor radioactive decay processes. In any sample of a given radioactive substance, the number of atoms of the radioactive isotope must decrease with time as their nuclei decay to nuclei of a more stable isotope.

Activity is usually measured in disintegrations per second dps or disintegrations per minute dpm. The activity of a sample is directly proportional to the number of atoms of the radioactive isotope in the sample:. Here, the symbol k is the radioactive decay constant, which has units of inverse time e. Because radioactive decay is a first-order process, the time required for half of the nuclei in any sample of a radioactive isotope to decay is a constant, called the half-life of the isotope.

The half-life tells us how radioactive an isotope is the number of decays per unit time ; thus it is the most commonly cited property of any radioisotope. For a given number of atoms, isotopes with shorter half-lives decay more rapidly, undergoing a greater number of radioactive decays per unit time than do isotopes with longer half-lives. The half-lives of several isotopes are listed in Table In our earlier discussion, we used the half-life of a first-order reaction to calculate how long the reaction had been occurring.

Because nuclear decay reactions follow first-order kinetics and have a rate constant that is independent of temperature and the chemical or physical environment, we can perform similar calculations using the half-lives of isotopes to estimate the ages of geological and archaeological artifacts. The techniques that have been developed for this application are known as radioisotope dating techniques. The most common method for measuring the age of ancient objects is carbon dating.

As a result, the CO 2 that plants use as a carbon source for synthesizing organic compounds always includes a certain proportion of 14 CO 2 molecules as well as nonradioactive 12 CO 2 and 13 CO 2. Any animal that eats a plant ingests a mixture of organic compounds that contains approximately the same proportions of carbon isotopes as those in the atmosphere.

Comparing the disintegrations per minute per gram of carbon from an archaeological sample with those from a recently living sample enables scientists to estimate the age of the artifact, as illustrated in Example Radiocarbon Dating. A plot of the specific activity of 14 C versus age for a number of archaeological samples shows an inverse linear relationship between 14 C content a log scale and age a linear scale. In , the remains of an apparently prehistoric man were found in a melting glacier in the Italian Alps.

Analysis of the 14 C content of samples of wood from his tools gave a decay rate of 8. How long ago did the man die? It is believed that humans first arrived in the Western Hemisphere during the last Ice Age, presumably by traveling over an exposed land bridge between Siberia and Alaska. Archaeologists have estimated that this occurred about 11, yr ago, but some argue that recent discoveries in several sites in North and South America suggest a much earlier arrival.

Analysis of a sample of charcoal from a fire in one such site gave a 14 C decay rate of 0. What is the approximate age of the sample? The half-life of a reaction is the time required for the reactant concentration to decrease to one-half its initial value. The half-life of a first-order reaction is a constant that is related to the rate constant for the reaction: Radioactive decay reactions are first-order reactions.

The rate of decay, or activity, of a sample of a radioactive substance is the decrease in the number of radioactive nuclei per unit time. Skills to Develop To know how to use half-lives to describe the rates of first-order reactions. Subtract the remaining concentration from the initial concentration.

Then divide by the initial concentration, multiplying the fraction by to obtain the percent completion. What is the half-life for the reaction under these conditions? If a flask that originally contains 0. Answer a 4. Radioactive Decay Rates Radioactivity, or radioactive decay, is the emission of a particle or a photon that results from the spontaneous decomposition of the unstable nucleus of an atom. Note Radioactive decay is a first-order process. Radioisotope Dating Techniques In our earlier discussion, we used the half-life of a first-order reaction to calculate how long the reaction had been occurring.

Answer 30, yr. Summary The half-life of a first-order reaction is independent of the concentration of the reactants. The half-lives of radioactive isotopes can be used to date objects.

## Radiometric dating, radioactive dating or radioisotope dating is a technique used to date All ordinary matter is made up of combinations of chemical elements, each with its . This temperature is what is known as closure temperature and represents the temperature below which the mineral is a closed system to isotopes. Radiometric dating (often called radioactive dating) is a way to find out how old All ordinary matter is made up of combinations of chemical elements, each with.

Early methods relied on uranium and thorium minerals, but potassium—argon, rubidium—strontium, samarium—neodymium, and carbon—carbon are now of considerable importance. Uranium decays to lead with a half-life of 4. It is important that the radioactive isotope be contained within the sample being dated.

Radiometric dating is a means of determining the "age" of a mineral specimen by determining the relative amounts present of certain radioactive elements. By "age" we mean the elapsed time from when the mineral specimen was formed.

Another approach to describing reaction rates is based on the time required for the concentration of a reactant to decrease to one-half its initial value. If two reactions have the same order, the faster reaction will have a shorter half-life, and the slower reaction will have a longer half-life.

## 21.3 Radioactive Decay

Radiometric dating , radioactive dating or radioisotope dating is a technique used to date materials such as rocks or carbon , in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay. Together with stratigraphic principles , radiometric dating methods are used in geochronology to establish the geologic time scale. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts. Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.

## Radioactive Decay Rates

Radiocarbon dating is a method that provides objective age estimates for carbon-based materials that originated from living organisms. The impact of the radiocarbon dating technique on modern man has made it one of the most significant discoveries of the 20th century. Archaeology and other human sciences use radiocarbon dating to prove or disprove theories. Over the years, carbon 14 dating has also found applications in geology, hydrology, geophysics, atmospheric science, oceanography, paleoclimatology and even biomedicine. Radiocarbon, or carbon 14, is an isotope of the element carbon that is unstable and weakly radioactive. The stable isotopes are carbon 12 and carbon Carbon 14 is continually being formed in the upper atmosphere by the effect of cosmic ray neutrons on nitrogen 14 atoms. It is rapidly oxidized in air to form carbon dioxide and enters the global carbon cycle. Plants and animals assimilate carbon 14 from carbon dioxide throughout their lifetimes. When they die, they stop exchanging carbon with the biosphere and their carbon 14 content then starts to decrease at a rate determined by the law of radioactive decay.

Radioactive isotope , also called radioisotope, radionuclide, or radioactive nuclide , any of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha , beta , and gamma rays.

Radiometric dating, often called radioactive dating, is a technique used to determine the age of materials such as rocks. It is based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates. It is the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself, and it can be used to date a wide range of natural and man-made materials.

## Radiometric dating

Radioactive decay is the loss of elementary particles from an unstable nucleus, ultimately changing the unstable element into another more stable element. Each type of decay emits a specific particle which changes the type of product produced. For information on each type of decay, read the page Decay pathways. In terms of entropy, radioactive decay can be defined as the tendency for matter and energy to gain inert uniformity or stability. The unstable nucleus then releases radiation in order to gain stability. However, there exists a lighter isotope of Beryllium which contains 4 protons and only 3 neutrons, which gives a total mass of 7 amu. This lighter isotope decays into Lithium-7 through electron capture. A proton from Beryllium-7 captures a single electron and becomes a neutron. This element gains stability by passing through various types of decays 19 steps-- also known as the Uranium series and is converted into Pb atomic number Because of this, the study of decay is independent of the element's environment.

## Radioactive isotope

An Essay on Radiometric Dating. By Jonathon Woolf http: Radiometric dating methods are the strongest direct evidence that geologists have for the age of the Earth. All these methods point to Earth being very, very old -- several billions of years old. Young-Earth creationists -- that is, creationists who believe that Earth is no more than 10, years old -- are fond of attacking radiometric dating methods as being full of inaccuracies and riddled with sources of error.

## radiometric dating

Scientists look at half-life decay rates of radioactive isotopes to estimate when a particular atom might decay. A useful application of half-lives is radioactive dating. This has to do with figuring out the age of ancient things. It might take a millisecond, or it might take a century. But if you have a large enough sample, a pattern begins to emerge.

## Nuclear Chemistry: Half-Lives and Radioactive Dating

Radiometric dating often called radioactive dating is a way to find out how old something is. The method compares the amount of a naturally occurring radioactive isotope and its decay products, in samples. The method uses known decay rates. It is the main way to learn the age of rocks and other geological features, including the age of the Earth itself. It may be used to date a wide range of natural and man-made materials.

A process for determining the age of an object by measuring the amount of a given radioactive material it contains. If one knows how much of this radioactive material was present initially in the object by determining how much of the material has decayed , and one knows the half-life of the material, one can deduce the age of the object. The simple days of immediately understanding what SWF means are far behind us. Online dating has made acronyms more inscrutable—and more fun—than ever. Take our quiz and find out. We hope this made it a little bit easier to navigate those stormy dating waters.

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RADIOACTIVITY