Periodic table of chemical elements (periodic table)- classification of chemical elements, establishing the dependence of various properties of elements on the charge of the atomic nucleus. The system is a graphic expression of the periodic law established by the Russian chemist D. I. Mendeleev in 1869. Its original version was developed by D.I. Mendeleev in 1869-1871 and established the dependence of the properties of elements on their atomic weight (in modern terms, on atomic mass). In total, several hundred options for depicting the periodic system (analytical curves, tables, geometric figures, etc.) have been proposed. In the modern version of the system, it is assumed that elements are summarized in a two-dimensional table, in which each column (group) defines the main physical and chemical properties, and the rows represent periods that are to a certain extent similar to each other.
Periodic table of chemical elements by D.I. Mendeleev
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The discovery made by the Russian chemist Mendeleev played (by far) the most important role in the development of science, namely in the development of atomic-molecular science. This discovery made it possible to obtain the most understandable and easy-to-learn ideas about simple and complex chemical compounds. It is only thanks to the table that we have the concepts about the elements that we use in the modern world. In the twentieth century, the predictive role of the periodic system in assessing the chemical properties of transuranium elements, shown by the creator of the table, emerged.
Developed in the 19th century, Mendeleev's periodic table in the interests of the science of chemistry provided a ready-made systematization of the types of atoms for the development of PHYSICS in the 20th century (physics of the atom and the atomic nucleus). At the beginning of the twentieth century, physicists, through research, established that the atomic number (also known as atomic number) is also a measure of the electrical charge of the atomic nucleus of this element. And the number of the period (i.e., horizontal series) determines the number of electron shells of the atom. It also turned out that the number of the vertical row of the table determines the quantum structure of the outer shell of the element (thus, elements of the same row are obliged to have similar chemical properties).
The discovery of the Russian scientist marked a new era in the history of world science; this discovery allowed not only to make a huge leap in chemistry, but was also invaluable for a number of other areas of science. The periodic table provided a coherent system of information about the elements, based on it, it became possible to draw scientific conclusions, and even anticipate some discoveries.
Periodic Table One of the features of the periodic table is that the group (column in the table) has more significant expressions of the periodic trend than for periods or blocks. Nowadays, the theory of quantum mechanics and atomic structure explains the group essence of elements by the fact that they have the same electronic configurations of valence shells, and as a result, elements that are located within the same column have very similar (identical) features of the electronic configuration, with similar chemical properties. There is also a clear tendency for a stable change in properties as the atomic mass increases. It should be noted that in some areas of the periodic table (for example, in blocks D and F), horizontal similarities are more noticeable than vertical ones.
The periodic table contains groups that are assigned serial numbers from 1 to 18 (from left to right), according to the international group naming system. In the past, Roman numerals were used to identify groups. In America, there was a practice of placing after the Roman numeral, the letter “A” when the group is located in blocks S and P, or the letter “B” for groups located in block D. The identifiers used at that time are the same as the latter the number of modern indexes in our time (for example, the name IVB corresponds to elements of group 4 in our time, and IVA is the 14th group of elements). In European countries of that time, a similar system was used, but here, the letter “A” referred to groups up to 10, and the letter “B” - after 10 inclusive. But groups 8,9,10 had ID VIII, as one triple group. These group names ceased to exist after the new IUPAC notation system, which is still used today, came into force in 1988.
Many groups received unsystematic names of a herbal nature (for example, “alkaline earth metals”, or “halogens”, and other similar names). Groups 3 to 14 did not receive such names, due to the fact that they are less similar to each other and have less compliance with vertical patterns; they are usually called either by number or by the name of the first element of the group (titanium, cobalt, etc.) .
Chemical elements belonging to the same group of the periodic table show certain trends in electronegativity, atomic radius and ionization energy. In one group, from top to bottom, the radius of the atom increases as the energy levels are filled, the valence electrons of the element move away from the nucleus, while the ionization energy decreases and the bonds in the atom weaken, which simplifies the removal of electrons. Electronegativity also decreases, this is a consequence of the fact that the distance between the nucleus and valence electrons increases. But there are also exceptions to these patterns, for example, electronegativity increases, instead of decreasing, in group 11, in the direction from top to bottom. There is a line in the periodic table called “Period”.
Among the groups, there are those in which horizontal directions are more significant (unlike others in which vertical directions are more important), such groups include block F, in which lanthanides and actinides form two important horizontal sequences.
Elements show certain patterns in atomic radius, electronegativity, ionization energy, and electron affinity energy. Due to the fact that for each subsequent element the number of charged particles increases, and electrons are attracted to the nucleus, the atomic radius decreases from left to right, along with this the ionization energy increases, and as the bond in the atom increases, the difficulty of removing an electron increases. Metals located on the left side of the table are characterized by a lower electron affinity energy indicator, and accordingly, on the right side the electron affinity energy indicator is higher for non-metals (not counting the noble gases).
Different regions of the periodic table, depending on which shell of the atom the last electron is located on, and in view of the importance of the electron shell, are usually described as blocks.
The S-block includes the first two groups of elements (alkali and alkaline earth metals, hydrogen and helium).
The P-block includes the last six groups, from 13 to 18 (according to IUPAC, or according to the system adopted in America - from IIIA to VIIIA), this block also includes all metalloids.
Block - D, groups 3 to 12 (IUPAC, or IIIB to IIB in American), this block includes all transition metals.
Block - F, is usually placed outside the periodic table, and includes lanthanides and actinides.
Anyone who went to school remembers that one of the compulsory subjects to study was chemistry. You might like her, or you might not like her - it doesn't matter. And it is likely that much knowledge in this discipline has already been forgotten and is not used in life. However, everyone probably remembers D.I. Mendeleev’s table of chemical elements. For many, it has remained a multi-colored table, where certain letters are written in each square, indicating the names of chemical elements. But here we will not talk about chemistry as such, and describe hundreds of chemical reactions and processes, but we will tell you how the periodic table appeared in the first place - this story will be interesting to any person, and indeed to all those who are hungry for interesting and useful information .
A little background
Back in 1668, the outstanding Irish chemist, physicist and theologian Robert Boyle published a book in which many myths about alchemy were debunked, and in which he discussed the need to search for indecomposable chemical elements. The scientist also gave a list of them, consisting of only 15 elements, but admitted the idea that there may be more elements. This became the starting point not only in the search for new elements, but also in their systematization.
A hundred years later, the French chemist Antoine Lavoisier compiled a new list, which already included 35 elements. 23 of them were later found to be indecomposable. But the search for new elements continued by scientists around the world. And the main role in this process was played by the famous Russian chemist Dmitry Ivanovich Mendeleev - he was the first to put forward the hypothesis that there could be a relationship between the atomic mass of elements and their location in the system.
Thanks to painstaking work and comparison of chemical elements, Mendeleev was able to discover the connection between the elements, in which they can be one, and their properties are not something taken for granted, but represent a periodically repeating phenomenon. As a result, in February 1869, Mendeleev formulated the first periodic law, and already in March his report “Relationship of properties with the atomic weight of elements” was presented to the Russian Chemical Society by the historian of chemistry N. A. Menshutkin. Then, in the same year, Mendeleev’s publication was published in the journal “Zeitschrift fur Chemie” in Germany, and in 1871, another German journal “Annalen der Chemie” published a new extensive publication by the scientist dedicated to his discovery.
Creating the periodic table
By 1869, the main idea had already been formed by Mendeleev, and in a fairly short time, but for a long time he could not formalize it into any orderly system that would clearly display what was what. In one of the conversations with his colleague A.A. Inostrantsev, he even said that he had everything already worked out in his head, but he couldn’t put everything into a table. After this, according to Mendeleev’s biographers, he began painstaking work on his table, which lasted three days without breaks for sleep. They tried all sorts of ways to organize elements into a table, and the work was also complicated by the fact that at that time science did not yet know about all the chemical elements. But, despite this, the table was still created, and the elements were systematized.
The legend of Mendeleev's dream
Many have heard the story that D.I. Mendeleev dreamed about his table. This version was actively disseminated by the aforementioned Mendeleev’s associate A. A. Inostrantsev as a funny story with which he entertained his students. He said that Dmitry Ivanovich went to bed and in a dream clearly saw his table, in which all the chemical elements were arranged in the right order. After this, the students even joked that 40° vodka was discovered in the same way. But there were still real prerequisites for the story with sleep: as already mentioned, Mendeleev worked on the table without sleep or rest, and Inostrantsev once found him tired and exhausted. During the day, Mendeleev decided to take a short rest, and some time later, he woke up abruptly, immediately took a piece of paper and drew a ready-made table on it. But the scientist himself refuted this whole story with the dream, saying: “I’ve been thinking about it, maybe for twenty years, and you think: I was sitting and suddenly... it’s ready.” So the legend of the dream may be very attractive, but the creation of the table was only possible through hard work.
Further work
Between 1869 and 1871, Mendeleev developed the ideas of periodicity toward which the scientific community was inclined. And one of the important stages of this process was the understanding that any element in the system should have, based on the totality of its properties in comparison with the properties of other elements. Based on this, and also relying on the results of research into changes in glass-forming oxides, the chemist was able to make corrections to the values of the atomic masses of some elements, including uranium, indium, beryllium and others.
Mendeleev, of course, wanted to quickly fill the empty cells that remained in the table, and in 1870 he predicted that chemical elements unknown to science would soon be discovered, the atomic masses and properties of which he was able to calculate. The first of these were gallium (discovered in 1875), scandium (discovered in 1879) and germanium (discovered in 1885). Then the predictions continued to be realized, and eight more new elements were discovered, including: polonium (1898), rhenium (1925), technetium (1937), francium (1939) and astatine (1942-1943). By the way, in 1900, D.I. Mendeleev and the Scottish chemist William Ramsay came to the conclusion that the table should also include elements of group zero - until 1962 they were called inert gases, and after that - noble gases.
Organization of the periodic table
Chemical elements in D.I. Mendeleev’s table are arranged in rows, in accordance with the increase in their mass, and the length of the rows is selected so that the elements in them have similar properties. For example, noble gases such as radon, xenon, krypton, argon, neon and helium are difficult to react with other elements and also have low chemical reactivity, which is why they are located in the far right column. And the elements in the left column (potassium, sodium, lithium, etc.) react well with other elements, and the reactions themselves are explosive. Simply put, within each column, elements have similar properties that vary from one column to the next. All elements up to No. 92 are found in nature, and from No. 93 artificial elements begin, which can only be created in laboratory conditions.
In its original version, the periodic system was understood only as a reflection of the order existing in nature, and there were no explanations as to why everything should be this way. It was only when quantum mechanics appeared that the true meaning of the order of elements in the table became clear.
Lessons in the creative process
Speaking about what lessons of the creative process can be drawn from the entire history of the creation of D. I. Mendeleev’s periodic table, we can cite as an example the ideas of the English researcher in the field of creative thinking Graham Wallace and the French scientist Henri Poincaré. Let's give them briefly.
According to the studies of Poincaré (1908) and Graham Wallace (1926), there are four main stages of creative thinking:
- Preparation– the stage of formulating the main problem and the first attempts to solve it;
- Incubation– a stage during which there is a temporary distraction from the process, but work on finding a solution to the problem is carried out on a subconscious level;
- Insight– the stage at which the intuitive solution is located. Moreover, this solution can be found in a situation that is completely unrelated to the problem;
- Examination– the stage of testing and implementation of a solution, at which this solution is tested and its possible further development.
As we can see, in the process of creating his table, Mendeleev intuitively followed precisely these four stages. How effective this is can be judged by the results, i.e. by the fact that the table was created. And given that its creation was a huge step forward not only for chemical science, but also for all of humanity, the above four stages can be applied both to the implementation of small projects and to the implementation of global plans. The main thing to remember is that not a single discovery, not a single solution to a problem can be found on its own, no matter how much we want to see them in a dream and no matter how much we sleep. In order for something to work out, it doesn’t matter whether it’s creating a table of chemical elements or developing a new marketing plan, you need to have certain knowledge and skills, as well as skillfully use your potential and work hard.
We wish you success in your endeavors and successful implementation of your plans!
A chemical element is a collective term that describes a collection of atoms of a simple substance, that is, one that cannot be divided into any simpler (according to the structure of their molecules) components. Imagine being given a piece of pure iron and being asked to separate it into its hypothetical constituents using any device or method ever invented by chemists. However, you can't do anything; the iron will never be divided into something simpler. A simple substance - iron - corresponds to the chemical element Fe.
Theoretical definition
The experimental fact noted above can be explained using the following definition: a chemical element is an abstract collection of atoms (not molecules!) of the corresponding simple substance, i.e. atoms of the same type. If there was a way to look at each of the individual atoms in the piece of pure iron mentioned above, then they would all be iron atoms. In contrast, a chemical compound such as iron oxide always contains at least two different kinds of atoms: iron atoms and oxygen atoms.
Terms you should know
Atomic mass: The mass of protons, neutrons, and electrons that make up an atom of a chemical element.
Atomic number: The number of protons in the nucleus of an element's atom.
Chemical symbol: a letter or pair of Latin letters representing the designation of a given element.
Chemical compound: a substance that consists of two or more chemical elements combined with each other in a certain proportion.
Metal: An element that loses electrons in chemical reactions with other elements.
Metalloid: An element that reacts sometimes as a metal and sometimes as a non-metal.
Non-metal: An element that seeks to gain electrons in chemical reactions with other elements.
Periodic Table of Chemical Elements: A system for classifying chemical elements according to their atomic numbers.
Synthetic element: One that is produced artificially in a laboratory and is generally not found in nature.
Natural and synthetic elements
Ninety-two chemical elements occur naturally on Earth. The rest were obtained artificially in laboratories. A synthetic chemical element is typically the product of nuclear reactions in particle accelerators (devices used to increase the speed of subatomic particles such as electrons and protons) or nuclear reactors (devices used to control the energy released by nuclear reactions). The first synthetic element with atomic number 43 was technetium, discovered in 1937 by Italian physicists C. Perrier and E. Segre. Apart from technetium and promethium, all synthetic elements have nuclei larger than uranium. The last synthetic chemical element to receive its name is livermorium (116), and before it was flerovium (114).
Two dozen common and important elements
| Name | Symbol | Percentage of all atoms * | Properties of chemical elements (under normal room conditions) |
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| In the Universe | In the earth's crust | In sea water | In the human body |
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| Aluminum | Al | - | 6,3 | - | - | Lightweight, silver metal |
| Calcium | Ca | - | 2,1 | - | 0,02 | Found in natural minerals, shells, bones |
| Carbon | WITH | - | - | - | 10,7 | The basis of all living organisms |
| Chlorine | Cl | - | - | 0,3 | - | Poisonous gas |
| Copper | Cu | - | - | - | - | Red metal only |
| Gold | Au | - | - | - | - | Yellow metal only |
| Helium | He | 7,1 | - | - | - | Very light gas |
| Hydrogen | N | 92,8 | 2,9 | 66,2 | 60,6 | The lightest of all elements; gas |
| Iodine | I | - | - | - | - | Non-metal; used as an antiseptic |
| Iron | Fe | - | 2,1 | - | - | Magnetic metal; used to produce iron and steel |
| Lead | Pb | - | - | - | - | Soft, heavy metal |
| Magnesium | Mg | - | 2,0 | - | - | Very light metal |
| Mercury | Hg | - | - | - | - | Liquid metal; one of two liquid elements |
| Nickel | Ni | - | - | - | - | Corrosion-resistant metal; used in coins |
| Nitrogen | N | - | - | - | 2,4 | Gas, the main component of air |
| Oxygen | ABOUT | - | 60,1 | 33,1 | 25,7 | Gas, the second important one air component |
| Phosphorus | R | - | - | - | 0,1 | Non-metal; important for plants |
| Potassium | TO | - | 1.1 | - | - | Metal; important for plants; usually called "potash" |
* If the value is not specified, then the element is less than 0.1 percent.
The Big Bang as the root cause of matter formation
What chemical element was the very first in the Universe? Scientists believe the answer to this question lies in stars and the processes by which stars are formed. The universe is believed to have come into being at some point in time between 12 and 15 billion years ago. Until this moment, nothing existing except energy is thought of. But something happened that turned this energy into a huge explosion (the so-called Big Bang). In the next seconds after the Big Bang, matter began to form.
The first simplest forms of matter to appear were protons and electrons. Some of them combine to form hydrogen atoms. The latter consists of one proton and one electron; it is the simplest atom that can exist.
Slowly, over long periods of time, hydrogen atoms began to cluster together in certain areas of space, forming dense clouds. The hydrogen in these clouds was pulled into compact formations by gravitational forces. Eventually these clouds of hydrogen became dense enough to form stars.
Stars as chemical reactors of new elements
A star is simply a mass of matter that generates energy from nuclear reactions. The most common of these reactions involves the combination of four hydrogen atoms forming one helium atom. Once stars began to form, helium became the second element to appear in the Universe.
As stars get older, they switch from hydrogen-helium nuclear reactions to other types. In them, helium atoms form carbon atoms. Later, carbon atoms form oxygen, neon, sodium and magnesium. Later still, neon and oxygen combine with each other to form magnesium. As these reactions continue, more and more chemical elements are formed.
The first systems of chemical elements
More than 200 years ago, chemists began to look for ways to classify them. In the mid-nineteenth century, about 50 chemical elements were known. One of the questions that chemists sought to resolve. boiled down to the following: is a chemical element a substance completely different from any other element? Or some elements related to others in some way? Is there a general law that unites them?
Chemists proposed various systems of chemical elements. For example, the English chemist William Prout in 1815 suggested that the atomic masses of all elements are multiples of the mass of the hydrogen atom, if we take it equal to unity, i.e. they must be integers. At that time, the atomic masses of many elements had already been calculated by J. Dalton in relation to the mass of hydrogen. However, if this is approximately the case for carbon, nitrogen, and oxygen, then chlorine with a mass of 35.5 did not fit into this scheme.
The German chemist Johann Wolfgang Dobereiner (1780 – 1849) showed in 1829 that three elements of the so-called halogen group (chlorine, bromine and iodine) could be classified by their relative atomic masses. The atomic weight of bromine (79.9) turned out to be almost exactly the average of the atomic weights of chlorine (35.5) and iodine (127), namely 35.5 + 127 ÷ 2 = 81.25 (close to 79.9). This was the first approach to constructing one of the groups of chemical elements. Dobereiner discovered two more such triads of elements, but he was unable to formulate a general periodic law.
How did the periodic table of chemical elements appear?
Most of the early classification schemes were not very successful. Then, around 1869, almost the same discovery was made by two chemists at almost the same time. Russian chemist Dmitri Mendeleev (1834-1907) and German chemist Julius Lothar Meyer (1830-1895) proposed organizing elements that have similar physical and chemical properties into an ordered system of groups, series, and periods. At the same time, Mendeleev and Meyer pointed out that the properties of chemical elements periodically repeat depending on their atomic weights.
Today, Mendeleev is generally considered the discoverer of the periodic law because he took one step that Meyer did not. When all the elements were arranged in the periodic table, some gaps appeared. Mendeleev predicted that these were places for elements that had not yet been discovered.
However, he went even further. Mendeleev predicted the properties of these not yet discovered elements. He knew where they were located on the periodic table, so he could predict their properties. Remarkably, every chemical element Mendeleev predicted, gallium, scandium, and germanium, was discovered less than ten years after he published his periodic law.
Short form of the periodic table
There have been attempts to count how many options for the graphic representation of the periodic table were proposed by different scientists. It turned out that there were more than 500. Moreover, 80% of the total number of options are tables, and the rest are geometric figures, mathematical curves, etc. As a result, four types of tables found practical application: short, semi-long, long and ladder (pyramidal). The latter was proposed by the great physicist N. Bohr.
The picture below shows the short form.
In it, chemical elements are arranged in ascending order of their atomic numbers from left to right and from top to bottom. Thus, the first chemical element of the periodic table, hydrogen, has atomic number 1 because the nuclei of hydrogen atoms contain one and only one proton. Likewise, oxygen has atomic number 8 since the nuclei of all oxygen atoms contain 8 protons (see figure below).
The main structural fragments of the periodic system are periods and groups of elements. In six periods, all cells are filled, the seventh is not yet completed (elements 113, 115, 117 and 118, although synthesized in laboratories, have not yet been officially registered and do not have names).
The groups are divided into main (A) and secondary (B) subgroups. Elements of the first three periods, each containing one row, are included exclusively in the A-subgroups. The remaining four periods include two rows.
Chemical elements in the same group tend to have similar chemical properties. Thus, the first group consists of alkali metals, the second - alkaline earth metals. Elements in the same period have properties that slowly change from an alkali metal to a noble gas. The figure below shows how one of the properties, atomic radius, changes for individual elements in the table.
Long period form of the periodic table
It is shown in the figure below and is divided in two directions, rows and columns. There are seven period rows, as in the short form, and 18 columns, called groups or families. In fact, the increase in the number of groups from 8 in the short form to 18 in the long form is obtained by placing all the elements in periods, starting from the 4th, not in two, but in one line.
Two different numbering systems are used for groups, as shown at the top of the table. The Roman numeral system (IA, IIA, IIB, IVB, etc.) has traditionally been popular in the United States. Another system (1, 2, 3, 4, etc.) is traditionally used in Europe and was recommended for use in the USA several years ago.
The appearance of the periodic tables in the figures above is a little misleading, as with any such published table. The reason for this is that the two groups of elements shown at the bottom of the tables should actually be located within them. The lanthanides, for example, belong to period 6 between barium (56) and hafnium (72). Additionally, actinides belong to period 7 between radium (88) and rutherfordium (104). If they were inserted into a table, it would become too wide to fit on a piece of paper or a wall chart. Therefore, it is customary to place these elements at the bottom of the table.
If you find the periodic table difficult to understand, you are not alone! Although it can be difficult to understand its principles, learning how to use it will help you when studying science. First, study the structure of the table and what information you can learn from it about each chemical element. Then you can begin to study the properties of each element. And finally, using the periodic table, you can determine the number of neutrons in an atom of a particular chemical element.
Steps
Part 1
Table structure- For example, the first row of the table contains hydrogen, which has atomic number 1, and helium, which has atomic number 2. However, they are located on opposite edges because they belong to different groups.
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Learn about groups that contain elements with similar physical and chemical properties. The elements of each group are located in the corresponding vertical column. They are typically identified by the same color, which helps identify elements with similar physical and chemical properties and predict their behavior. All elements of a particular group have the same number of electrons in their outer shell.
- Hydrogen can be classified as both alkali metals and halogens. In some tables it is indicated in both groups.
- In most cases, the groups are numbered from 1 to 18, and the numbers are placed at the top or bottom of the table. Numbers can be specified in Roman (eg IA) or Arabic (eg 1A or 1) numerals.
- When moving along a column from top to bottom, you are said to be “browsing a group.”
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Find out why there are empty cells in the table. Elements are ordered not only according to their atomic number, but also by group (elements in the same group have similar physical and chemical properties). Thanks to this, it is easier to understand how a particular element behaves. However, as the atomic number increases, elements that fall into the corresponding group are not always found, so there are empty cells in the table.
- For example, the first 3 rows have empty cells because transition metals are only found from atomic number 21.
- Elements with atomic numbers 57 to 102 are classified as rare earth elements, and are usually placed in their own subgroup in the lower right corner of the table.
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Each row of the table represents a period. All elements of the same period have the same number of atomic orbitals in which the electrons in the atoms are located. The number of orbitals corresponds to the period number. The table contains 7 rows, that is, 7 periods.
- For example, atoms of elements of the first period have one orbital, and atoms of elements of the seventh period have 7 orbitals.
- As a rule, periods are designated by numbers from 1 to 7 on the left of the table.
- As you move along a line from left to right, you are said to be “scanning the period.”
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Learn to distinguish between metals, metalloids and non-metals. You will better understand the properties of an element if you can determine what type it is. For convenience, in most tables metals, metalloids, and nonmetals are designated by different colors. Metals are on the left and non-metals are on the right side of the table. Metalloids are located between them.
Part 2
Element designations-
Each element is designated by one or two Latin letters. As a rule, the element symbol is shown in large letters in the center of the corresponding cell. A symbol is a shortened name for an element that is the same in most languages. Element symbols are commonly used when conducting experiments and working with chemical equations, so it is helpful to remember them.
- Typically, element symbols are abbreviations of their Latin name, although for some, especially recently discovered elements, they are derived from the common name. For example, helium is represented by the symbol He, which is close to the common name in most languages. At the same time, iron is designated as Fe, which is an abbreviation of its Latin name.
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Pay attention to the full name of the element if it is given in the table. This element "name" is used in regular texts. For example, "helium" and "carbon" are names of elements. Usually, although not always, the full names of the elements are listed below their chemical symbol.
- Sometimes the table does not indicate the names of the elements and only gives their chemical symbols.
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Find the atomic number. Typically, the atomic number of an element is located at the top of the corresponding cell, in the middle or in the corner. It may also appear under the element's symbol or name. Elements have atomic numbers from 1 to 118.
- The atomic number is always an integer.
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Remember that the atomic number corresponds to the number of protons in an atom. All atoms of an element contain the same number of protons. Unlike electrons, the number of protons in the atoms of an element remains constant. Otherwise, you would get a different chemical element!
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The periodic table, or periodic table of chemical elements, begins in the upper left corner and ends at the end of the last row of the table (lower right corner). The elements in the table are arranged from left to right in increasing order of their atomic number. The atomic number shows how many protons are contained in one atom. In addition, as the atomic number increases, the atomic mass also increases. Thus, by the location of an element in the periodic table, its atomic mass can be determined.
As you can see, each subsequent element contains one more proton than the element preceding it. This is obvious when you look at the atomic numbers. Atomic numbers increase by one as you move from left to right. Because elements are arranged in groups, some table cells are left empty.
Knowing the formulation of the periodic law and using D.I. Mendeleev’s periodic system of elements, one can characterize any chemical element and its compounds. It is convenient to put together such a characteristic of a chemical element according to plan.
I. Symbol of a chemical element and its name.
II. The position of a chemical element in the periodic table of elements D.I. Mendeleev:
- serial number;
- period number;
- group number;
- subgroup (main or secondary).
III. Structure of an atom of a chemical element:
- charge of the nucleus of an atom;
- relative atomic mass of a chemical element;
- number of protons;
- number of electrons;
- number of neutrons;
- number of electronic levels in an atom.
IV. Electronic and electron-graphic formulas of an atom, its valence electrons.
V. Type of chemical element (metal or non-metal, s-, p-, d- or f-element).
VI. Formulas of the highest oxide and hydroxide of a chemical element, characteristics of their properties (basic, acidic or amphoteric).
VII. Comparison of the metallic or non-metallic properties of a chemical element with the properties of neighboring elements by period and subgroup.
VIII. The maximum and minimum oxidation state of an atom.
For example, we will provide a description of a chemical element with serial number 15 and its compounds according to their position in D.I. Mendeleev’s periodic table of elements and the structure of the atom.
I. We find in D.I. Mendeleev’s table a cell with the number of a chemical element, write down its symbol and name.
Chemical element number 15 is Phosphorus. Its symbol is R.
II. Let us characterize the position of the element in D.I. Mendeleev’s table (period number, group, subgroup type).
Phosphorus is in the main subgroup of group V, in the 3rd period.
III. We will provide a general description of the composition of an atom of a chemical element (nuclear charge, atomic mass, number of protons, neutrons, electrons and electronic levels).
The nuclear charge of the phosphorus atom is +15. The relative atomic mass of phosphorus is 31. The nucleus of an atom contains 15 protons and 16 neutrons (31 - 15 = 16). The phosphorus atom has three energy levels containing 15 electrons.
IV. We compose the electronic and electron-graphic formulas of the atom, marking its valence electrons.
The electronic formula of the phosphorus atom is: 15 P 1s 2 2s 2 2p 6 3s 2 3p 3.
Electron-graphic formula for the external level of a phosphorus atom: on the third energy level, on the 3s sublevel, there are two electrons (two arrows in the opposite direction are written in one cell), on three p-sublevels there are three electrons (one is written in each of the three cells arrows having the same direction).
Valence electrons are electrons of the outer level, i.e. 3s2 3p3 electrons.
V. Determine the type of chemical element (metal or non-metal, s-, p-, d-or f-element).
Phosphorus is a non-metal. Since the latter sublevel in the phosphorus atom, which is filled with electrons, is the p-sublevel, Phosphorus belongs to the family of p-elements.
VI. We compose formulas of higher oxide and hydroxide of phosphorus and characterize their properties (basic, acidic or amphoteric).
Higher phosphorus oxide P 2 O 5 exhibits the properties of an acidic oxide. The hydroxide corresponding to the higher oxide, H 3 PO 4, exhibits the properties of an acid. Let us confirm these properties with equations of the types of chemical reactions:
P 2 O 5 + 3 Na 2 O = 2Na 3 PO 4
H 3 PO 4 + 3NaOH = Na 3 PO 4 + 3H 2 O
VII. Let's compare the non-metallic properties of phosphorus with the properties of neighboring elements by period and subgroup.
Phosphorus' subgroup neighbor is nitrogen. Phosphorus' period neighbors are silicon and sulfur. The nonmetallic properties of atoms of chemical elements of the main subgroups with increasing atomic number increase in periods and decrease in groups. Therefore, the non-metallic properties of phosphorus are more pronounced than those of silicon and less pronounced than those of nitrogen and sulfur.
VIII. We determine the maximum and minimum oxidation state of the phosphorus atom.
The maximum positive oxidation state for chemical elements of the main subgroups is equal to the group number. Phosphorus is in the main subgroup of the fifth group, so the maximum oxidation state of phosphorus is +5.
The minimum oxidation state for nonmetals in most cases is the difference between the group number and the number eight. Thus, the minimum oxidation state of phosphorus is -3.
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