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Nissa has a masters degree in chemistry and has taught high school science and college level chemistry.
Let's imagine a pair of identical twins. These twins have the same temperament, and since they're identical, it is very hard to tell them apart unless you examine them closely. When it is time for their annual physical, the twins need to step on a weighing scale, and when they do, one weighs slightly more than the other. In terms of chemistry, we can say that these twins are like isotopes of each other.
Atoms and elements are made of protons, neutrons and electrons. The nucleus is made of protons and neutrons, and the electrons surround the nucleus, as shown in the illustration below. The sum of the number of protons and the number of neutrons is equal to the atomic mass.
In a given element, the number of neutrons can be different from each other, while the number of protons is not. These different versions of the same element are called isotopes. Isotopes are atoms with the same number of protons but that have a different number of neutrons. Since the atomic number is equal to the number of protons and the atomic mass is the sum of protons and neutrons, we can also say that isotopes are elements with the same atomic number but different mass numbers.
Let us take a look at an example.
The three are all isotopes of hydrogen. As you can see, they have the same atomic number, or number of protons, (number at the lower left of the element) but different atomic masses (number at the upper left of the element).
The number of neutrons can be calculated by calculating the difference between the atomic mass and atomic number. We can see that for the isotopes of hydrogen, they have varying number of neutrons. For protium, the number of neutrons is zero; for deuterium, the number of neutrons is one; and for tritium, the number of neutrons is two.
Going back to our comparison with identical twins, we can say that these three isotopes of hydrogen are like identical triplets of each other - they may appear to be identical outside, but they are different inside, and they also have different names.
A very popular element, carbon, also has isotopes. There are three isotopes of carbon: carbon-12, carbon-13 and carbon-14. The numbers that are after the carbon refer to the atomic mass.
The most common and abundant isotope of carbon is carbon-12. Looking at the percentages below each carbon isotope, we see that almost 98.9% of the carbon that is found is in the form of carbon-12. The least abundant form of carbon is carbon-14, with an abundance of less than 0.0001%. If we calculate the number of neutrons for each carbon isotope, we can see that they differ from each other. For carbon-12, we have 6 neutrons; for carbon-13, we have 7 neutrons; and for carbon-14, we have 8 neutrons.
You may notice if we look at the atomic masses of elements in the periodic table that they are rarely ever whole numbers, just like for carbon where the atomic mass is 12.011. This is because the atomic mass of carbon is based on the average atomic masses of its isotopes and the abundance of each isotope.
There are two main types of isotopes, and these are radioactive isotopes and stable isotopes. Stable isotopes have a stable combination of protons and neutrons, so they have stable nuclei and do not undergo decay. These isotopes do not pose dangerous effects to living things, like radioactive isotopes.
They are typically useful when performing experiments in the environment and in the field of geochemistry. These isotopes can help determine the chemical composition and age of minerals and other geologic objects. Some examples of stable isotopes are isotopes of carbon, potassium, calcium and vanadium.
Radioactive isotopes have an unstable combination of protons and neutrons, so they have unstable nuclei. Because these isotopes are unstable, they undergo decay, and in the process can emit alpha, beta and gamma rays.
Radioactive isotopes can be useful in different industries, such as food, agriculture, archaeology and medicine. For instance, in the food industry, the food we eat undergoes a process called food irradiation, where it is exposed to gamma rays. This kills bacteria in the food. In medicine, radioactive isotopes emit gamma rays to help detect tumors. In archaeology, if an object contains carbon and we are unsure of its age, the isotope of carbon, carbon-14, is used to determine its age with a process called radiocarbon dating.
There are different types of radioactive isotopes. Long-lived radioactive isotopes were created when the solar system was formed, and they've been present for billions of years. Examples of long-lived radioactive isotopes include potassium-40, rubidium-87 and uranium-238.
Cosmogenic isotopes are formed when the atmosphere reacts with the rays emitted from stars or when geological materials on the Earth's surface are irradiated by cosmic rays directly. Carbon-14, chlorine-36 and hydrogen-3, also known as tritium, are all cosmogenic isotopes.
Anthropogenic isotopes are man-made or result from human activities, such as testing weapons and processing nuclear fuels. These isotopes are useful in the fields of oceanography and hydrology since they can be used to study flow, currents and sedimentation rates. Anthropogenic isotopes include some cosmogenic isotopes, such as carbon-14, chlorine-36 and hydrogen-3, as well as krypton-85.
Radiogenic isotopes are produced when isotopes undergo radioactive decay. These isotopes are helpful in the geological field, where they can help determine the timeline of geological events and predict fracturing. In hydrology, they can serve as hydrologic tracers, helping scientists determine the path of water flow and flow rates. Examples of radiogenic isotopes include argon-40 and hydrogen-4.
The isotopes of an element are like different versions of an element - they have the same number of protons but different number of neutrons. In turn, we can also say that isotopes of an element have the same atomic numbers but different atomic mass. The number of neutrons can be determined by taking the difference between the atomic mass and the atomic number. The atomic masses of the elements that are reflected in the periodic table are calculated from averages of the different isotopes and their abundance.
There are two types of isotopes: stable and radioactive. These two types of isotopes have many uses in different industries - medical, agricultural and food, among others. Stable isotopes do not undergo decay and are not harmful to living things. Radioactive isotopes are unstable, so they undergo decay and are, in general, harmful to living things. There are four types of radioactive isotopes: anthropogenic, long-lived, cosmogenic and radiogenic.
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Back To CourseMCAT Test: Practice and Study Guide
88 chapters | 863 lessons