Atoms of isotopes of one element differ in number. Chemical and molecular properties

It has been established that every chemical element found in nature is a mixture of isotopes (hence they have fractional atomic masses). To understand how isotopes differ from one another, it is necessary to consider in detail the structure of the atom. An atom forms a nucleus and an electron cloud. The mass of an atom is influenced by electrons moving at stunning speeds through orbitals in the electron cloud, neutrons and protons that make up the nucleus.

What are isotopes

Isotopes is a type of atom of a chemical element. There are always equal numbers of electrons and protons in any atom. Since they have opposite charges (electrons are negative, and protons are positive), the atom is always neutral (this elementary particle does not carry a charge, it is zero). When an electron is lost or captured, an atom loses neutrality, becoming either a negative or a positive ion.
Neutrons have no charge, but their number in the atomic nucleus of the same element can vary. This does not in any way affect the neutrality of the atom, but it does affect its mass and properties. For example, any isotope of a hydrogen atom contains one electron and one proton. But the number of neutrons is different. Protium has only 1 neutron, deuterium has 2 neutrons, and tritium has 3 neutrons. These three isotopes differ markedly from each other in properties.

Comparison of isotopes

How are isotopes different? They have different numbers of neutrons, different masses and different properties. Isotopes have identical structures of electron shells. This means that they are quite similar in chemical properties. Therefore, they are given one place in the periodic table.
Stable and radioactive (unstable) isotopes have been found in nature. The nuclei of atoms of radioactive isotopes are capable of spontaneously transforming into other nuclei. During the process of radioactive decay, they emit various particles.
Most elements have over two dozen radioactive isotopes. In addition, radioactive isotopes are artificially synthesized for absolutely all elements. In a natural mixture of isotopes, their content varies slightly.
The existence of isotopes made it possible to understand why, in some cases, elements with lower atomic mass have a higher atomic number than elements with higher atomic mass. For example, in the argon-potassium pair, argon includes heavy isotopes, and potassium contains light isotopes. Therefore, the mass of argon is greater than that of potassium.

ImGist determined that the differences between isotopes are as follows:

They have different numbers of neutrons.
Isotopes have different atomic masses.
The value of the mass of ion atoms affects their total energy and properties.

A certain element that has the same but different. They have nuclei with the same number and diversity. number, have the same structure of electron shells and occupy the same place in the periodicity. chemical system elements. The term "isotopes" was proposed in 1910 by F. Soddy to designate chemically indistinguishable varieties that differ in their physical properties. (primarily radioactive) Saints. Stable isotopes were first discovered in 1913 by J. Thomson using the so-called he developed. the method of parabolas - the prototype of the modern one. . He found that Ne has at least 2 varieties with a wt. parts 20 and 22. The names and symbols of isotopes are usually the names and symbols of the corresponding chemicals. elements; point to the top left of the symbol. For example, to indicate natural isotopes use the notation 35 Cl and 37 Cl; sometimes the element is also indicated at the bottom left, i.e. write 35 17 Cl and 37 17 Cl. Only isotopes of the lightest element, hydrogen, with wt. parts 1, 2 and 3 have special. names and symbols: (1 1 H), (D, or 2 1 H) and (T, or 3 1 H), respectively. Due to the large difference in masses, the behavior of these isotopes differs significantly (see,). Stable isotopes occur in all even and most odd elements with[ 83. The number of stable isotopes of elements with even numbers may be. equals 10 (e.g. y); Odd-numbered elements have no more than two stable isotopes. Known approx. 280 stable and more than 2000 radioactive isotopes of 116 natural and artificially obtained elements. For each element, the content of individual isotopes in nature. the mixture undergoes small fluctuations, which can often be neglected. More means. fluctuations in the isotopic composition are observed for meteorites and other celestial bodies. The constancy of the isotopic composition leads to the constancy of the elements found on Earth, which is the average value of the mass of a given element, found taking into account the abundance of isotopes in nature. Fluctuations in the isotopic composition of light elements are associated, as a rule, with changes in the isotopic composition during decomposition. processes occurring in nature (, etc.). For the heavy element Pb, variations in the isotopic composition of different samples are explained by different factors. content in, and other sources and - the ancestors of nature. . Differences in the properties of isotopes of a given element are called. . Important practical The task is to obtain from nature. mixtures of individual isotopes -

Definition

Neutrons have no charge, but their number in the atomic nucleus of the same element can vary. This does not in any way affect the neutrality of the atom, but it does affect its mass and properties. For example, any isotope of a hydrogen atom contains one electron and one proton. But the number of neutrons is different. Protium has only 1 neutron, deuterium has 2 neutrons, and tritium has 3 neutrons. These three isotopes differ markedly from each other in properties.

Comparison

They have different numbers of neutrons, different masses and different properties. Isotopes have identical structures of electron shells. This means that they are quite similar in chemical properties. Therefore, they are given one place in the periodic table.

Stable and radioactive (unstable) isotopes have been found in nature. The nuclei of atoms of radioactive isotopes are capable of spontaneously transforming into other nuclei. During the process of radioactive decay, they emit various particles.

Most elements have over two dozen radioactive isotopes. In addition, radioactive isotopes are artificially synthesized for absolutely all elements. In a natural mixture of isotopes, their content varies slightly.

The existence of isotopes made it possible to understand why, in some cases, elements with lower atomic mass have a higher atomic number than elements with higher atomic mass. For example, in the argon-potassium pair, argon includes heavy isotopes, and potassium contains light isotopes. Therefore, the mass of argon is greater than that of potassium.

Conclusions website

They have different numbers of neutrons.
Isotopes have different atomic masses.
The value of the mass of ion atoms affects their total energy and properties.

There is probably not a person on earth who has not heard about isotopes. But not everyone knows what it is. The phrase “radioactive isotopes” sounds especially frightening. These strange chemical elements terrify humanity, but in fact they are not as scary as they might seem at first glance.

Definition

To understand the concept of radioactive elements, it is necessary to first say that isotopes are samples of the same chemical element, but with different masses. What does it mean? The questions will disappear if we first remember the structure of the atom. It consists of electrons, protons and neutrons. The number of the first two elementary particles in the nucleus of an atom is always constant, while neutrons, which have their own mass, can occur in the same substance in different quantities. This circumstance gives rise to a variety of chemical elements with different physical properties.

Now we can give a scientific definition to the concept under study. So, isotopes are a collective set of chemical elements that are similar in properties, but have different masses and physical properties. According to more modern terminology, they are called a galaxy of nucleotides of a chemical element.

A little history

At the beginning of the last century, scientists discovered that the same chemical compound under different conditions can have different masses of electron nuclei. From a purely theoretical point of view, such elements could be considered new and they could begin to fill empty cells in D. Mendeleev’s periodic table. But there are only nine free cells in it, and scientists discovered dozens of new elements. In addition, mathematical calculations showed that the discovered compounds cannot be considered previously unknown, because their chemical properties fully corresponded to the characteristics of existing ones.

After lengthy discussions, it was decided to call these elements isotopes and place them in the same box as those whose nuclei contain the same number of electrons. Scientists have been able to determine that isotopes are just some variations of chemical elements. However, the causes of their occurrence and life expectancy have been studied for almost a century. Even at the beginning of the 21st century, it is impossible to say that humanity knows absolutely everything about isotopes.

Persistent and unstable variations

Each chemical element has several isotopes. Due to the fact that there are free neutrons in their nuclei, they do not always enter into stable bonds with the rest of the atom. After some time, free particles leave the nucleus, which changes its mass and physical properties. In this way, other isotopes are formed, which ultimately leads to the formation of a substance with an equal number of protons, neutrons and electrons.

Those substances that decay very quickly are called radioactive isotopes. They release a large number of neutrons into space, forming powerful ionizing gamma radiation, known for its strong penetrating power, which negatively affects living organisms.

More stable isotopes are not radioactive, since the number of free neutrons released by them is not capable of generating radiation and significantly affecting other atoms.

Quite a long time ago, scientists established one important pattern: each chemical element has its own isotopes, persistent or radioactive. Interestingly, many of them were obtained in laboratory conditions, and their presence in natural form is small and is not always detected by instruments.

Distribution in nature

Under natural conditions, substances are most often found whose isotope mass is directly determined by its ordinal number in D. Mendeleev’s table. For example, hydrogen, denoted by the symbol H, has an atomic number of 1, and its mass is equal to one. Its isotopes, 2H and 3H, are extremely rare in nature.

Even the human body has some radioactive isotopes. They enter through food in the form of carbon isotopes, which, in turn, are absorbed by plants from the soil or air and become part of organic matter during the process of photosynthesis. Therefore, humans, animals, and plants emit a certain background radiation. Only it is so low that it does not interfere with normal functioning and growth.

The sources that contribute to the formation of isotopes are the inner layers of the earth's core and radiation from space.

As you know, the temperature on a planet largely depends on its hot core. But only very recently it became clear that the source of this heat is a complex thermonuclear reaction in which radioactive isotopes participate.

Isotopic Decay

Since isotopes are unstable formations, it can be assumed that over time they always decay into more permanent nuclei of chemical elements. This statement is true because scientists have not been able to detect huge amounts of radioactive isotopes in nature. And most of those that were extracted in laboratories lasted from a couple of minutes to several days, and then turned back into ordinary chemical elements.

But there are also isotopes in nature that turn out to be very resistant to decay. They can exist for billions of years. Such elements were formed in those distant times, when the earth was still being formed, and there was not even a solid crust on its surface.

Radioactive isotopes decay and form again very quickly. Therefore, in order to facilitate the assessment of the stability of the isotope, scientists decided to consider the category of its half-life.

Half life

It may not be immediately clear to all readers what is meant by this concept. Let's define it. The half-life of an isotope is the time during which a conventional half of the substance taken will cease to exist.

This does not mean that the rest of the connection will be destroyed in the same amount of time. In relation to this half, it is necessary to consider another category - the period of time during which its second part, that is, a quarter of the original amount of substance, will disappear. And this consideration continues ad infinitum. It can be assumed that it is simply impossible to calculate the time for complete disintegration of the initial amount of a substance, since this process is practically endless.

However, scientists, knowing the half-life, can determine how much of the substance existed at the beginning. These data are successfully used in related sciences.

In the modern scientific world, the concept of complete decay is practically not used. For each isotope, it is customary to indicate its half-life, which varies from a few seconds to many billions of years. The lower the half-life, the more radiation comes from the substance and the higher its radioactivity.

Fossil beneficiation

In some branches of science and technology, the use of relatively large quantities of radioactive substances is considered mandatory. However, under natural conditions there are very few such compounds.

It is known that isotopes are uncommon variants of chemical elements. Their number is measured in several percent of the most resistant variety. This is why scientists need to artificially enrich fossil materials.

Over the years of research, we have learned that the decay of an isotope is accompanied by a chain reaction. The released neutrons of one substance begin to influence another. As a result of this, heavy nuclei disintegrate into lighter ones and new chemical elements are obtained.

This phenomenon is called a chain reaction, as a result of which more stable but less common isotopes can be obtained, which are subsequently used in the national economy.

Application of decay energy

Scientists also found that during the decay of a radioactive isotope, a huge amount of free energy is released. Its amount is usually measured by the Curie unit, equal to the fission time of 1 g of radon-222 in 1 second. The higher this indicator, the more energy is released.

This became the reason for developing ways to use free energy. This is how atomic reactors appeared, into which a radioactive isotope is placed. Most of the energy released by it is collected and converted into electricity. Based on these reactors, nuclear power plants are created that provide the cheapest electricity. Smaller versions of such reactors are installed on self-propelled mechanisms. Given the danger of accidents, submarines are most often used as such vehicles. In the event of a reactor failure, the number of casualties on the submarine will be easier to minimize.

Another very scary use of half-life energy is atomic bombs. During World War II, they were tested on humans in the Japanese cities of Hiroshima and Nagasaki. The consequences were very sad. Therefore, there is an agreement in the world on the non-use of these dangerous weapons. At the same time, large states with a focus on militarization continue research in this area today. In addition, many of them, secretly from the world community, are producing atomic bombs, which are thousands of times more dangerous than those used in Japan.

Isotopes in medicine

For peaceful purposes, they have learned to use the decay of radioactive isotopes in medicine. By directing radiation to the affected area of the body, it is possible to stop the course of the disease or help the patient to recover completely.

But more often radioactive isotopes are used for diagnostics. The thing is that their movement and the nature of the cluster are most easily determined by the radiation they produce. Thus, a certain non-hazardous amount of a radioactive substance is introduced into the human body, and doctors use instruments to observe how and where it gets into.

In this way, they diagnose the functioning of the brain, the nature of cancerous tumors, and the peculiarities of the functioning of the endocrine and exocrine glands.

Application in archeology

It is known that living organisms always contain radioactive carbon-14, the half-life of which is 5570 years. In addition, scientists know how much of this element is contained in the body until the moment of death. This means that all cut trees emit the same amount of radiation. Over time, the radiation intensity decreases.

This helps archaeologists determine how long ago the wood from which the galley or any other ship was built died, and therefore the time of construction itself. This research method is called radioactive carbon analysis. Thanks to it, it is easier for scientists to establish the chronology of historical events.

When studying the properties of radioactive elements, it was discovered that the same chemical element can contain atoms with different nuclear masses. At the same time, they have the same nuclear charge, that is, these are not impurities of foreign substances, but the same substance.

What are isotopes and why do they exist?

In Mendeleev's periodic table, both this element and atoms of a substance with different nuclear masses occupy one cell. Based on the above, such varieties of the same substance were given the name “isotopes” (from the Greek isos - identical and topos - place). So, isotopes- these are varieties of a given chemical element, differing in the mass of atomic nuclei.

According to the accepted neutron-proton model of the nucleus, it was possible to explain the existence of isotopes as follows: the nuclei of some atoms of a substance contain different numbers of neutrons, but the same number of protons. In fact, the nuclear charge of isotopes of one element is the same, therefore, the number of protons in the nucleus is the same. Nuclei differ in mass; accordingly, they contain different numbers of neutrons.

Stable and unstable isotopes

Isotopes can be stable or unstable. To date, about 270 stable isotopes and more than 2000 unstable ones are known. Stable isotopes- These are varieties of chemical elements that can exist independently for a long time.

Most of unstable isotopes was obtained artificially. Unstable isotopes are radioactive, their nuclei are subject to the process of radioactive decay, that is, spontaneous transformation into other nuclei, accompanied by the emission of particles and/or radiation. Almost all radioactive artificial isotopes have very short half-lives, measured in seconds or even fractions of seconds.

How many isotopes can a nucleus contain?

The nucleus cannot contain an arbitrary number of neutrons. Accordingly, the number of isotopes is limited. Even number of protons elements, the number of stable isotopes can reach ten. For example, tin has 10 isotopes, xenon has 9, mercury has 7, and so on.

Those elements the number of protons is odd, can have only two stable isotopes. Some elements have only one stable isotope. These are substances such as gold, aluminum, phosphorus, sodium, manganese and others. Such variations in the number of stable isotopes of different elements are associated with the complex dependence of the number of protons and neutrons on the binding energy of the nucleus.

Almost all substances in nature exist in the form of a mixture of isotopes. The number of isotopes in a substance depends on the type of substance, atomic mass and the number of stable isotopes of a given chemical element.