Anyone who went to school remembers that one of the required subjects to study was chemistry. She could like it, or she could not like it - it does not matter. And it is likely that much knowledge in this discipline has already been forgotten and is not applied in life. However, everyone probably remembers the table of chemical elements of D. I. Mendeleev. For many, it has remained a multi-colored table, where certain letters are inscribed in each square, denoting 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 talk about how the periodic table appeared in general - this story will be of interest to any person, and indeed to all those who want 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 talked about the need to search for indecomposable chemical elements. The scientist also gave a list of them, consisting of only 15 elements, but allowed 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 a relationship between elements in which they can be one, and their properties are not something taken for granted, but are a periodically repeating phenomenon. As a result, in February 1869, Mendeleev formulated the first periodic law, and already in March, his report “The relationship of properties with the atomic weight of elements” was submitted 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 a new extensive publication of the scientist dedicated to his discovery was published by another German journal Annalen der Chemie.
Creating a Periodic Table
By 1869, the main idea had already been formed by Mendeleev, and in a fairly short time, but he could not formalize it into any sort of ordered system that clearly displays what was what, for a long time he could not. In one of the conversations with his colleague A. A. Inostrantsev, he even said that everything had already worked out in his head, but he could not bring everything to the table. After that, according to Mendeleev's biographers, he began painstaking work on his table, which lasted three days without a break for sleep. All sorts of ways to organize the elements in a table were sorted out, and the work was 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.
Legend of Mendeleev's dream
Many have heard the story that D. I. Mendeleev dreamed of his table. This version was actively distributed by the aforementioned colleague of Mendeleev, 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 he clearly saw his table, in which all the chemical elements were arranged in the right order. After that, the students even joked that 40° vodka was discovered in the same way. But there were still real prerequisites for the sleep story: as already mentioned, Mendeleev worked on the table without sleep and rest, and Inostrantsev once found him tired and exhausted. In the afternoon, Mendeleev decided to take a break, and some time later, he woke up abruptly, immediately took a piece of paper and depicted a ready-made table on it. But the scientist himself refuted this whole story with a dream, saying: “I’ve been thinking about it for maybe 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
In the period from 1869 to 1871, Mendeleev developed the ideas of periodicity, to 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 be located based on the totality of its properties in comparison with the properties of other elements. Based on this, and also based on the results of research in the change of glass-forming oxides, the chemist managed to amend the values of the atomic masses of some elements, among which were uranium, indium, beryllium and others.
Of course, Mendeleev wanted to fill the empty cells that remained in the table as soon as possible, 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 forecasts continued to be realized, and eight more new elements were discovered, among them: 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 elements of the zero group should also be included in the table - until 1962 they were called inert, and after - noble gases.
Organization of the periodic system
The chemical elements in the table of D. I. Mendeleev are arranged in rows, in accordance with the increase in their mass, and the length of the rows is chosen so that the elements in them have similar properties. For example, noble gases such as radon, xenon, krypton, argon, neon, and helium do not easily react with other elements, and also have low chemical activity, which is why they are located in the far right column. And the elements of the left column (potassium, sodium, lithium, etc.) react perfectly with other elements, and the reactions themselves are explosive. To put it simply, within each column, the elements have similar properties, varying from one column to the next. All elements up to No. 92 are found in nature, and with No. 93 artificial elements begin, which can only be created in the laboratory.
In its original version, the periodic system was understood only as a reflection of the order existing in nature, and there were no explanations why everything should be that way. And only when quantum mechanics appeared, the true meaning of the order of elements in the table became clear.
Creative Process Lessons
Speaking about what lessons of the creative process can be drawn from the entire history of the creation of the periodic table of D. I. Mendeleev, one 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 take them briefly.
According to Poincaré (1908) and Graham Wallace (1926), there are four main stages in creative thinking:
- Training- the stage of formulating the main task and the first attempts to solve it;
- Incubation- the stage during which there is a temporary distraction from the process, but work on finding a solution to the problem is carried out at a subconscious level;
- insight- the stage at which the intuitive solution is found. Moreover, this solution can be found in a situation that is absolutely not relevant to the task;
- Examination- the stage of testing and implementation of the solution, at which the verification of this solution and its possible further development takes place.
As we can see, in the process of creating his table, Mendeleev intuitively followed these four stages. How effective this is can be judged by the results, i.e. because the table was created. And given that its creation was a huge step forward not only for chemical science, but for the whole 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 to succeed, whether it is the creation of a table of chemical elements or the development of 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!
Attempts to systematize the chemical elements were made by many scientists. But only in 1869, D. I. Mendeleev managed to create a classification of elements, which established the relationship and dependence of chemicals and the charge of the atomic nucleus.
Story
The modern formulation of the periodic law is as follows: the properties of chemical elements, as well as the forms and properties of compounds of elements, are in a periodic dependence on the charge of the nucleus of the element's atoms.
By the time the law was discovered, 63 chemical elements were known. However, the atomic masses of many of these elements have been erroneously determined.
D. And Mendeleev himself in 1869 formulated his law as a periodic dependence on the magnitude of the atomic weights of elements, since in the 19th century science did not yet have information about the structure of the atom. However, the scientist's brilliant foresight allowed him to understand more deeply than all his contemporaries the patterns that determine the periodicity of the properties of elements and substances. He took into account not only the increase in the atomic mass, but also the already known properties of substances and elements, and, taking the idea of periodicity as a basis, he was able to accurately predict the existence and properties of elements and substances unknown at that time to science, correct the atomic masses of a number of elements, correctly arrange the elements in system, leaving empty spaces and making permutations.
Rice. 1. D. I. Mendeleev.
There is a myth that Mendeleev dreamed of the periodic system. However, this is only a beautiful story, which is not a proven fact.
Structure of the periodic system
The periodic system of chemical elements of D. I. Mendeleev is a graphic reflection of his own law. Elements are arranged in a table according to a certain chemical and physical meaning. By the location of the element, you can determine its valence, the number of electrons, and many other features. The table is divided horizontally into large and small periods, and vertically into groups.
Rice. 2. Periodic table.
There are 7 periods that begin with an alkali metal and end with substances that have non-metallic properties. Groups, in turn, consisting of 8 columns, are divided into main and secondary subgroups.
The further development of science showed that the periodic repetition of the properties of elements at certain intervals, especially clearly manifested in 2 and 3 small periods, is explained by the repetition of the electronic structure of the external energy levels, where valence electrons are located, due to which chemical bonds and new substances are formed in reactions. Therefore, in each vertical column-group there are elements with repeating characteristic features. This is clearly manifested in groups where there are families of very active alkali metals (group I, main subgroup) and non-halogen metals (group VII, main subgroup). From left to right along the period, the number of electrons increases from 1 to 8, while there is a decrease in the metallic properties of the elements. Thus, the metallic properties manifest themselves the stronger, the fewer electrons there are in the outer level.
Rice. 3. Small and large periods in the periodic table.
Such properties of atoms as ionization energy, electron affinity energy and electronegativity are also periodically repeated. These quantities are related to the ability of an atom to donate an electron from an external level (ionization) or to keep an alien electron at its external level (electron affinity). Total ratings received: 146.
If the periodic table seems difficult for you to understand, you are not alone! Although it can be difficult to understand its principles, learning to work with it will help in the study of natural sciences. To get started, study the structure of the table and what information can be learned from it about each chemical element. Then you can start exploring 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-
As you can see, each next 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. Since the elements are arranged in groups, some table cells remain empty.
- 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 on opposite ends because they belong to different groups.
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Learn about groups that include elements with similar physical and chemical properties. The elements of each group are located in the corresponding vertical column. As a rule, they are indicated by the same color, which helps to 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 the outer shell.
- Hydrogen can be attributed both to the group of alkali metals and to the group of 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 given in Roman (eg IA) or Arabic (eg 1A or 1) numerals.
- When moving along the column from top to bottom, they say that you are "browsing the 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 according to groups (elements of the same group have similar physical and chemical properties). This makes it easier to understand how an 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, since transition metals are found only from atomic number 21.
- Elements with atomic numbers from 57 to 102 belong to the rare earth elements, and they are usually placed in a separate 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 electrons are located in atoms. The number of orbitals corresponds to the period number. The table contains 7 rows, that is, 7 periods.
- For example, the atoms of the elements of the first period have one orbital, and the atoms of the elements of the seventh period have 7 orbitals.
- As a rule, periods are indicated 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 through a 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 belongs to. For convenience, in most tables, metals, metalloids and non-metals are indicated 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 an abbreviated name for an element that is the same in most languages. When doing experiments and working with chemical equations, the symbols of the elements are commonly used, so it is useful to remember them.
- Typically, element symbols are shorthand for their Latin name, although for some, especially recently discovered elements, they are derived from the common name. For example, helium is denoted 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 "name" of the element is used in normal texts. For example, "helium" and "carbon" are the names of the elements. Usually, though not always, the full names of the elements are given below their chemical symbol.
- Sometimes the names of the elements are not indicated in the table and only their chemical symbols are given.
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Find the atomic number. Usually the atomic number of an element is located at the top of the corresponding cell, in the middle or in the corner. It can also appear below the symbol or element 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, another chemical element would have turned out!
- The atomic number of an element can also be used to determine the number of electrons and neutrons in an atom.
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Usually the number of electrons is equal to the number of protons. The exception is the case when the atom is ionized. Protons have a positive charge and electrons have a negative charge. Since atoms are usually neutral, they contain the same number of electrons and protons. However, an atom can gain or lose electrons, in which case it becomes ionized.
- Ions have an electrical charge. If there are more protons in the ion, then it has a positive charge, in which case a plus sign is placed after the element symbol. If an ion contains more electrons, it has a negative charge, which is indicated by a minus sign.
- The plus and minus signs are omitted if the atom is not an ion.
The graphic representation of the Periodic Law is the Periodic System (table). The horizontal rows of the system are called periods, and the vertical columns are called groups.
In total, there are 7 periods in the system (table), and the period number is equal to the number of electron layers in the atom of the element, the number of the external (valence) energy level, and the value of the main quantum number for the highest energy level. Each period (except the first) begins with an s-element - an active alkali metal and ends with an inert gas, which is preceded by a p-element - an active non-metal (halogen). If we move along the period from left to right, then with an increase in the charge of the nuclei of atoms of chemical elements of small periods, the number of electrons at the external energy level will increase, as a result of which the properties of the elements change - from typically metallic (because there is an active alkali metal at the beginning of the period), through amphoteric (the element exhibits the properties of both metals and non-metals) to non-metallic (active non-metal - halogen at the end of the period), i.e. metallic properties gradually weaken and non-metallic ones increase.
In large periods, with increasing nuclear charge, the filling of electrons is more difficult, which explains a more complex change in the properties of elements compared to elements of small periods. So, in even rows of long periods, with increasing nuclear charge, the number of electrons in the outer energy level remains constant and equal to 2 or 1. Therefore, while the electrons are filling the level following the outer (second from the outside), the properties of elements in even rows change slowly. When moving to odd rows, with an increase in the nuclear charge, the number of electrons in the external energy level increases (from 1 to 8), the properties of the elements change in the same way as in small periods.
DEFINITION
Vertical columns in the Periodic system are groups of elements with a similar electronic structure and are chemical analogues. Groups are designated by Roman numerals from I to VIII. The main (A) and secondary (B) subgroups are distinguished, the first of which contain s- and p-elements, the second - d - elements.
The subgroup number A indicates the number of electrons in the outer energy level (the number of valence electrons). For elements of B-subgroups, there is no direct relationship between the group number and the number of electrons in the outer energy level. In A-subgroups, the metallic properties of the elements increase, and the non-metallic properties decrease with increasing charge of the nucleus of the element's atom.
There is a relationship between the position of the elements in the Periodic system and the structure of their atoms:
- atoms of all elements of the same period have an equal number of energy levels, partially or completely filled with electrons;
— atoms of all elements of A subgroups have an equal number of electrons at the external energy level.
A plan for characterizing a chemical element based on its position in the Periodic Table
Usually, a characteristic of a chemical element based on its position in the Periodic system is given according to the following plan:
- indicate the symbol of the chemical element, as well as its name;
- indicate the serial number, number of the period and group (type of subgroup) in which the element is located;
- indicate the nuclear charge, mass number, number of electrons, protons and neutrons in the atom;
- write down the electronic configuration and indicate the valence electrons;
- draw electron-graphic formulas for valence electrons in the ground and excited (if possible) states;
- indicate the family of the element, as well as its type (metal or non-metal);
- compare the properties of a simple substance with the properties of simple substances formed by elements neighboring in a subgroup;
- compare the properties of a simple substance with the properties of simple substances formed by elements neighboring in a period;
- indicate the formulas of higher oxides and hydroxides with a brief description of their properties;
- indicate the values of the minimum and maximum oxidation states of a chemical element.
Characteristics of a chemical element using magnesium (Mg) as an example
Consider the characteristics of a chemical element using the example of magnesium (Mg) according to the plan described above:
1. Mg - magnesium.
2. Ordinal number - 12. The element is in period 3, in group II, A (main) subgroup.
3. Z=12 (nuclear charge), M=24 (mass number), e=12 (number of electrons), p=12 (number of protons), n=24-12=12 (number of neutrons).
4. 12 Mg 1s 2 2s 2 2p 6 3s 2 – electronic configuration, valence electrons 3s 2 .
5. Basic state
excited state
6. s-element, metal.
7. The highest oxide - MgO - exhibits the main properties:
MgO + H 2 SO 4 \u003d MgSO 4 + H 2 O
MgO + N 2 O 5 \u003d Mg (NO 3) 2
As a magnesium hydroxide, the base Mg (OH) 2 corresponds, which exhibits all the typical properties of bases:
Mg(OH) 2 + H 2 SO 4 = MgSO 4 + 2H 2 O
8. The degree of oxidation "+2".
9. The metallic properties of magnesium are more pronounced than those of beryllium, but weaker than those of calcium.
10. The metallic properties of magnesium are less pronounced than those of sodium, but stronger than those of aluminum (neighboring elements of the 3rd period).
Examples of problem solving
EXAMPLE 1
Exercise Characterize the chemical element sulfur based on its position in the Periodic Table of D.I. Mendeleev Solution 1. S - sulfur. 2. Ordinal number - 16. The element is in the 3rd period, in the VI group, A (main) subgroup.
3. Z=16 (nuclear charge), M=32 (mass number), e=16 (number of electrons), p=16 (number of protons), n=32-16=16 (number of neutrons).
4. 16 S 1s 2 2s 2 2p 6 3s 2 3p 4 – electronic configuration, valence electrons 3s 2 3p 4 .
5. Basic state
excited state
6. p-element, non-metal.
7. The highest oxide - SO 3 - exhibits acidic properties:
SO 3 + Na 2 O \u003d Na 2 SO 4
8. The hydroxide corresponding to the higher oxide - H 2 SO 4, exhibits acidic properties:
H 2 SO 4 + 2NaOH \u003d Na 2 SO 4 + 2H 2 O
9. Minimum oxidation state "-2", maximum - "+6"
10. The non-metallic properties of sulfur are less pronounced than those of oxygen, but stronger than those of selenium.
11. The non-metallic properties of sulfur are more pronounced than those of phosphorus, but weaker than those of chlorine (adjacent elements in the 3rd period).
EXAMPLE 2
Exercise Describe the chemical element sodium based on its position in the Periodic Table of D.I. Mendeleev Solution 1. Na - sodium. 2. Ordinal number - 11. The element is in period 3, in group I, A (main) subgroup.
3. Z=11 (nuclear charge), M=23 (mass number), e=11 (number of electrons), p=11 (number of protons), n=23-11=12 (number of neutrons).
4. 11 Na 1s 2 2s 2 2p 6 3s 1 – electronic configuration, valence electrons 3s 1 .
5. Basic state
6. s-element, metal.
7. The highest oxide - Na 2 O - exhibits the main properties:
Na 2 O + SO 3 \u003d Na 2 SO 4
As sodium hydroxide, the base NaOH corresponds, which exhibits all the typical properties of bases:
2NaOH + H 2 SO 4 \u003d Na 2 SO 4 + 2H 2 O
8. The oxidation state "+1".
9. The metallic properties of sodium are more pronounced than those of lithium, but weaker than those of potassium.
10. The metallic properties of sodium are more pronounced than those of magnesium (the neighboring element of the 3rd period).
In nature, there are a lot of repeating sequences:
- seasons;
- Times of Day;
- days of the week…
In the middle of the 19th century, D.I. Mendeleev noticed that the chemical properties of elements also have a certain sequence (they say that this idea came to him in a dream). The result of the miraculous dreams of the scientist was the Periodic Table of Chemical Elements, in which D.I. Mendeleev arranged the chemical elements in order of increasing atomic mass. In the modern table, the chemical elements are arranged in ascending order of the atomic number of the element (the number of protons in the nucleus of an atom).
The atomic number is shown above the symbol of a chemical element, below the symbol is its atomic mass (the sum of protons and neutrons). Note that the atomic mass of some elements is a non-integer! Remember isotopes! Atomic mass is the weighted average of all the isotopes of an element that occur naturally under natural conditions.
Below the table are the lanthanides and actinides.
Metals, non-metals, metalloids
They are located in the Periodic Table to the left of the stepped diagonal line that starts with Boron (B) and ends with polonium (Po) (the exceptions are germanium (Ge) and antimony (Sb). It is easy to see that metals occupy most of the Periodic Table. The main properties of metals : solid (except mercury); shiny; good electrical and thermal conductors; ductile; malleable; easily donate electrons.
The elements to the right of the stepped diagonal B-Po are called non-metals. The properties of non-metals are directly opposite to the properties of metals: poor conductors of heat and electricity; fragile; non-forged; non-plastic; usually accept electrons.
Metalloids
Between metals and non-metals are semimetals(metalloids). They are characterized by the properties of both metals and non-metals. Semimetals have found their main industrial application in the production of semiconductors, without which no modern microcircuit or microprocessor is inconceivable.
Periods and groups
As mentioned above, the periodic table consists of seven periods. In each period, the atomic numbers of the elements increase from left to right.
The properties of elements in periods change sequentially: so sodium (Na) and magnesium (Mg), which are at the beginning of the third period, give up electrons (Na gives up one electron: 1s 2 2s 2 2p 6 3s 1; Mg gives up two electrons: 1s 2 2s 2 2p 6 3s 2). But chlorine (Cl), located at the end of the period, takes one element: 1s 2 2s 2 2p 6 3s 2 3p 5.
In groups, on the contrary, all elements have the same properties. For example, in the IA(1) group, all elements from lithium (Li) to francium (Fr) donate one electron. And all elements of group VIIA(17) take one element.
Some groups are so important that they have been given special names. These groups are discussed below.
Group IA(1). The atoms of the elements of this group have only one electron in the outer electron layer, so they easily donate one electron.
The most important alkali metals are sodium (Na) and potassium (K), since they play an important role in the process of human life and are part of salts.
Electronic configurations:
- Li- 1s 2 2s 1 ;
- Na- 1s 2 2s 2 2p 6 3s 1 ;
- K- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1
Group IIA(2). The atoms of the elements of this group have two electrons in the outer electron layer, which also give up during chemical reactions. The most important element is calcium (Ca) - the basis of bones and teeth.
Electronic configurations:
- Be- 1s 2 2s 2 ;
- mg- 1s 2 2s 2 2p 6 3s 2 ;
- Ca- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2
Group VIIA(17). Atoms of the elements of this group usually receive one electron each, because. on the outer electronic layer there are five elements each, and one electron is just missing to the "complete set".
The most famous elements of this group are: chlorine (Cl) - is part of salt and bleach; iodine (I) is an element that plays an important role in the activity of the human thyroid gland.
Electronic configuration:
- F- 1s 2 2s 2 2p 5 ;
- Cl- 1s 2 2s 2 2p 6 3s 2 3p 5 ;
- Br- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5
Group VIII(18). Atoms of the elements of this group have a fully "staffed" outer electron layer. Therefore, they "do not need" to accept electrons. And they don't want to give them away. Hence - the elements of this group are very "reluctant" to enter into chemical reactions. For a long time it was believed that they do not react at all (hence the name "inert", i.e. "inactive"). But chemist Neil Barlett discovered that some of these gases, under certain conditions, can still react with other elements.
Electronic configurations:
- Ne- 1s 2 2s 2 2p 6 ;
- Ar- 1s 2 2s 2 2p 6 3s 2 3p 6 ;
- kr- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6
Valence elements in groups
It is easy to see that within each group, the elements are similar to each other in their valence electrons (electrons of s and p orbitals located on the outer energy level).
Alkali metals have 1 valence electron each:
- Li- 1s 2 2s 1 ;
- Na- 1s 2 2s 2 2p 6 3s 1 ;
- K- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1
Alkaline earth metals have 2 valence electrons:
- Be- 1s 2 2s 2 ;
- mg- 1s 2 2s 2 2p 6 3s 2 ;
- Ca- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2
Halogens have 7 valence electrons:
- F- 1s 2 2s 2 2p 5 ;
- Cl- 1s 2 2s 2 2p 6 3s 2 3p 5 ;
- Br- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5
Inert gases have 8 valence electrons:
- Ne- 1s 2 2s 2 2p 6 ;
- Ar- 1s 2 2s 2 2p 6 3s 2 3p 6 ;
- kr- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6
For more information, see the article Valence and the Table of electronic configurations of atoms of chemical elements by periods.
Let us now turn our attention to the elements located in groups with symbols AT. They are located in the center of the periodic table and are called transition metals.
A distinctive feature of these elements is the presence of electrons in atoms that fill d-orbitals:
- sc- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 ;
- Ti- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2
Separate from the main table are located lanthanides and actinides are the so-called internal transition metals. In the atoms of these elements, electrons fill f-orbitals:
- Ce- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 4d 10 5s 2 5p 6 4f 1 5d 1 6s 2 ;
- Th- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 4d 10 5s 2 5p 6 4f 14 5d 10 6s 2 6p 6 6d 2 7s 2
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The periodic table, or periodic table of chemical elements, begins at the top left and ends at the end of the last line of the table (bottom right). The elements in the table are arranged from left to right in ascending order of their atomic number. The atomic number tells you how many protons are in one atom. In addition, as the atomic number increases, so does the atomic mass. Thus, by the location of an element in the periodic table, you can determine its atomic mass.
