# Advice 1: How to determine the charge of a chemical element

A chemical element consists of identical atoms possessing a combination of properties. These properties depend on many factors, primarily the structure of the atom. As the electron levels in the atom, how many electrons located at the external level, how far it is from the kernel - all this directly affects the behavior of item when entering in interaction with other elements. In General, the atom of any element is neutral, since the total negative charge of electrons is balanced by the total charge of the protons.
Instruction
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The famous periodic table, named after the great Russian scientist, the discoverer of the law of periodicity of properties of chemical elements, chemistry plays the role of a targeted and help Desk. Each chemical element has in it a very special cell "flat". The location of this cell in the table can accurately predict "the nature of the tenant", that is, what the properties of the element. And like any real apartment, each cell element has its own serial number.
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In order to determine what is the total charge of the atom the nucleus of any element, look at its serial number. The fact that he is numerically equal to the number of protons in the nucleus of its atom. And each proton, as already mentioned, bears a single positive charge. The truth in the nucleus in addition to protons, there are still particles that are called neutrons. But are they as easy to understand from their names, do not carry any charge.
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For example, one of the most active elements of the periodic table – the alkali metal rubidium. It is the first main group of the sixth period. Its number 37. Therefore, the total positive charge of the nucleus of an atom of rubidium is 37.
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Check it out. Any atom is neutral, therefore, the rubidium atom has to be 37 electrons to balance the charge of the proton nucleus. In the table cell, which is rubidium, the composition of electrons at each level. Consider how many electrons, at all levels: 2+8+18+8+1 = 37. The total charge of electrons and protons = 0.
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Another example. The most refractory of all existing, metal tungsten, which is in side the sixth group, the eighth period at number 74. As in the atom the electrons? Count: 2+8+18+32+12+2 = 74. Therefore, in order that the tungsten atom was neutral, the total positive charge of its nucleus must be equal to +74. The score has converged, all right.

# Advice 2: 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.
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