# Advice 1: How to learn to read the table of chemical elements of D. I. Mendeleev

The periodic system of chemical elements is a unique reference material which is necessary to properly "read" and then use the received information. In addition, the table by D. I. Mendeleyev is permitted material for all types of control, including even the exam in chemistry.
You will need
• The periodic system of chemical elements D. I. Mendeleev
Instruction
1
The periodic system is a multi-storey "house", which houses a large number of apartments. Each "tenant" or chemical element lives in his own apartment at a certain number, which is permanent. In addition, the element has a "name" or title, for example oxygen, boron or nitrogen. In addition to these data in each "apartment" or cage specified information such as relative atomic mass, which may be exact or rounded values.
2
As in any home, there are "entrances": the group. And the groups the elements are arranged left and right, forming subgroups. Depending on which side has more of them, that is called the main subgroup. The other group, respectively, would be side. This table also includes "floors" or periods. Moreover, periods can be as big (consist of two rows) and small (only one row).
3
The table can show the structure of the atom elements, each of which has a positively charged nucleus consisting of protons and neutrons, and orbiting negatively charged electrons. The number of protons and electrons is numerically equal and is defined in the table according to the serial number of the item. For example, the chemical element sulfur is number 16, therefore, will have 16 protons and 16 electrons.
4
To determine the number of neutrons (neutral particles also located in the nucleus) subtract the relative atomic mass of an element by its serial number. For example, iron has a relative atomic mass of 56 and a sequence number 26. Therefore, the 56 – 26 = 30 protons in iron.
5
Electrons are at different distances from the nucleus, forming electron levels. To determine the number (or energy) levels, you need to look at the period number in which the element is located. For example, aluminum is 3 the period, therefore, it will have 3 levels.
6
The number of the group (but only for main group), you can define a higher valence. For example, the elements of the first group of the main group (lithium, sodium, potassium, etc.) have valence 1. Accordingly, elements of the second group (beryllium, magnesium, calcium, etc.) will have a valency equal to 2.
7
Also at the table, you can perform the properties of the elements. From left to right, the metallic properties weaken, and non-amplified. This is well illustrated by example 2, the period starts on the alkaline metal is sodium, then the alkali earth metal is magnesium, after the amphoteric element is aluminum, then the non-metals silicon, phosphorus, sulfur, and ends the period of gaseous substances – chlorine and argon. In the next period there is a similar dependence.
8
Top-down is also observed the pattern – metallic properties increase and nonmetallic weaken. That is, for example, cesium is much more active compared to sodium.
For convenience, it is better to use a colored version of table.

The discovery of the periodic law and creation of an ordered system of chemical elements D. I. Mendeleyev became the apogee of the development of chemistry in the nineteenth century. Scientists have been compiled and systematized extensive material knowledge about the properties of elements.
Instruction
1
In the XIX century there were no ideas about the structure of the atom. The opening of D. I. Mendeleev was only a generalization of experimental facts, but their physical meaning has long remained unclear. When the first data on the structure of the nucleus and the distribution of electrons in atoms, it is possible to look at the periodic law and the system elements in new ways. Table of D. I. Mendeleev makes it possible to visually trace the periodicity of properties of elements found in nature.
2
Each element in the table is assigned a specific sequence number (H - 1, Li - 2, Be - 3, etc.). This number corresponds to the charge of the nucleus (number of protons in the nucleus) and the number of electrons rotating around the nucleus. The number of protons, therefore, equal to the number of electrons, and this suggests that under normal conditions, the atom is electrically neutral.
3
The division into seven periods is happening to the energy levels of the atom. The atoms of the first period have a single-level electronic shell, the second duplex, and the third a three-tier, etc. When filling a new energy level starts a new period.
4
The first elements of every period are characterized by atoms with one electron at the outer level, are atoms of alkali metals. The period ends with the atoms of noble gases have completely filled outer electron energy level: in the first period, noble gases have 2 electrons in the next - 8. It is because of the similar structure of the electron shells of the group of elements have similar physical and chemical properties.
5
In the table of D. I. Mendeleev present 8 major subgroups. Such a number is due to the maximum possible number of electrons on the energy level.
6
At the bottom of the periodic system selected lanthanides and actinides as a separate series.
7
Using the periodic table you can observe the periodicity of the following properties of the elements: the radius of the atom, the volume of the atom; ionization potential; the strength of the affinity with the electron; the electronegativity of the atom; oxidation; physical properties of potential compounds.
8
For example, the radii of atoms, when viewed along a period decreases from left to right; grow downwards, if you look along the band.
9
A clear periodicity arrangement of elements in the table Mendeleyev rationally owing to the continuous nature of the filling of electron energy levels.

# Advice 3: How many elements in the periodic table

The periodic law is the basis of modern chemistry and to explain the patterns of change of properties of chemical elements, was discovered by D. I. Mendeleev in 1869. The physical meaning of this law is revealed in the study of the complex structure of the atom.
In the XIX century it was believed that atomic mass is the main characteristic of the element, therefore for the classification of substances used it. Now the atoms and identificeret determine the magnitude of the charge of their nuclei (protons and ordinal position in the periodic table). However, atomic mass of elements with some exceptions (for example, atomic mass of potassium is less than the atomic weight of argon) is increased in proportion to their nuclear charge.

With increasing atomic mass and observed periodic variation of properties of elements and their compounds. This metallicity and nemetallicheskie of atoms, atomic radius and volume, ionization potential, electron affinity, electronegativity, oxidation States, physical properties of compounds (boiling point, melting point, density), their basicity, or acidity afternote.

## How many elements in the modern periodic table

The periodic table graphically expresses which he discovered the periodic law. In the modern periodic table contains 112 chemical elements (last – Materi, Darmstadt, Rentgene and Copernici). According to recent reports, opened and the next 8 elements (up to 120, inclusive), but not all of them got their names, and these elements are still few publications are present.
Each item occupies a cell in the periodic table and has a sequence number corresponding to the charge of the nucleus of its atom.

## How to build a periodic system

The structure of the periodic system represented by seven periods, with ten rows and eight groups. Each period starts with alkali metal and ends with noble gas. The exception is the first period starts with hydrogen, and a seventh incomplete period.

The periods are divided into small and large. Small periods (first, second, third) consists of a single horizontal row large (four, five, six) – two horizontal rows. The upper rows in the larger periods are called even, lower – odd.

In the sixth period of the table after lanthanum (number 57) there are 14 elements, similar properties for lanthanum, the lanthanides. They are made in the lower part of the table separately. The same applies to the actinides, after actinium (#89) and largely repeating its properties.
Even-numbered rows of large periods (4, 6, 8, 10) is filled just metals.

Elements in groups show the same higher valence in oxides and other compounds, and this value corresponds to the group number. Main groups contain elements of small and large periods, the side – just big. Top to bottom the metallic properties are intensified, non – weakened. All the atoms of the side sub-groups – metals.

# Advice 4: The history of the discovery of the periodic table

The periodic table of chemical elements has become one of the most important events in the history of science and brought its Creator, Russian scientist Dmitry Mendeleev, the world. This extraordinary man managed to unite into a single concept all the chemical elements, but how he managed to open his famous table?

## History of the periodic table

By the mid-19th century, scientists were able to access sixty-three chemical element, but to build them in a coherent logical chain does not work. The elements had to be placed in order of increasing atomic mass and divide by similarity of chemical properties in groups.

For the first time his theory similar to the theory of periodic future, proposed by the musician and the chemist John Alexander Newland – however, the scientific community ignored his achievement. Offer Nulend not taken seriously because of his search for harmony and connection between music and chemistry.

Dmitri Mendeleev first published his periodic table in 1869 in the journal of the Russian chemical society. Also, a scientist sent notice of his discovery to all the world's leading chemists, after which he was repeatedly improved and modified the table, until it became what it is know today. What discovery Dmitri Mendeleev was periodic, and non-monotonic change of chemical properties of elements with increasing atomic mass. The final unification of theory in the periodic law occurred in 1871.

## The legend of Mendeleev

The most common legend is the opening of the table of Mendeleyev in a dream. The scientist himself has repeatedly ridiculed this myth, claiming that he invented the table for many years. According to another legend Dmitri Mendeleev invented vodka – it came after the defense scientists of the thesis "Reasoning about the connection of alcohol with water".

Mendeleev is still considered by many to be the discoverer of vodka, which he loved to do under the water-alcohol solution. The contemporaries of the scientist often laughed at the laboratory of Mendeleev, which he has equipped in the hollow of a giant oak.

Private jokes was rumored to be the passion of Dmitri Mendeleev by the weaving bags, which scientist did, living in Simferopol. In the future, he with his own hands was making containers of cardboard for the needs of the laboratory, for which he sarcastically called a master of suitcase cases.

Periodic table, except for the ordering of chemical elements in a single system, made it possible to predict the discovery of many new elements. However, at the same time, some of them scientists consider to be non-existent because they were incompatible with the concept of the periodic law. The most famous story at the time was the discovery of such new elements as koroni and ônebuliumö.
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