From the nineteenth century, scientists began to realize that chemical elements could be grouped into columns, formed by the gathering of elements with similar properties.
The number of chemical elements known to man has increased over the centuries, especially in the nineteenth. Look at the table:
Until the end of the century:
No. of CHEMICAL ELEMENTS
Some elements were known before 1650, such as Ag, C, As, Au, Hg, Pb, Sn, Sb, Cu, S. After so many chemists tried to classify the chemical elements, Dimitri Ivanovitch Mendeleyev was what stood out the most.
His work in classifying elements is still used today. He created a periodic table of the elements, which served as the basis for organizing the one we have today.
Mendeleyev noted that there is a periodicity of properties when chemical elements are placed in ascending order of their atomic masses.
Law of Periodicity - Many physical and chemical properties of elements vary periodically following their atomic numbers.
How to use the periodic table?
Each table in the table provides data for the chemical element: symbol, atomic mass, atomic number, element name, electrons in the layers, and whether the element is radioactive.
The horizontal rows are called periods. In them, the chemical elements are arranged in ascending order of their atomic numbers. The period order number indicates the number of energy levels or electronic layers of the element. The periodic table presents seven periods:
1st period - 2 elements
2nd period - 8 elements
3rd period - 8 elements
4th period - 18 elements
5th sentence - 18 elements
6th sentence - 32 elements
7th sentence - so far 30 elements
The vertical columns constitute the families or groups, in which the elements are assembled according to their chemical properties. Families or groups range from 1 to 18. Some families have names, such as:
1 - alkaline
2 - earth alkaline
13 - boron family
14 - carbon family
15 - nitrogen family
16 - chalcogen family
17 - family of halogens
18 - noble gases
From family 1 and 2 and 13 to 18 we call elements representative. From the family of 3 to 12 we call elements of transition.
The elements in the lanthanides and actinides series are the elements of transition. Since they are in group 3, as if they were in a “box” into the table, they are called internal transition elements. And the rest are called elements of external transition.
The chemical elements are grouped into three major groups: metals, non-metals and noble gases. Hydrogen (H) does not fit into any of these classifications because it has its own characteristics. Some tables show this division.
Metals are chemical elements that have several specific properties, such as gloss, thermal and electrical conductivity, malleability and ductility. All metals are solid at 25ºC and 1atm pressure except mercury (Hg) which is liquid under these conditions.
Almost all metals are bright as they are able to reflect light very well. Gold, silver and aluminum are examples of very bright metals. Metals are good electrical conductors.
As they are generally ductible, that is, they can be reduced to wires, they are used as such in conducting electricity. Metals conduct heat well.
A pure metal does not always have desirable properties for certain applications. This is why metal alloys are produced, where two or more metals are mixed. Examples are bronze and brass. Bronze is a mixture of copper, tin and brass is a mixture of copper and zinc.
Most alloys consist of two or more metals, but some contain nonmetals, such as carbon. The most widely used alloy of this type is steel. Nonmetals are poor conductors of electricity, almost lacking in brightness, not malleable or ductile. They tend to form anions (negative ions).
Noble or inert or rare gases make up about 1% of air. It is very difficult to get compounds with these gases. They rarely react because they are very stable. Its outer layers are completely filled with electrons. They are all in group 18 of the periodic table.
In the current periodic table, there are natural and artificial elements. Naturals are the elements found in nature and artificials are produced in laboratories.
Two are located before uranium (U-92), the so-called elements cisuranic, which are the technetium (Tc - 43) and the promethium (Pm - 61). Other artificial elements come after uranium, we call transuranic which are all others after U - 92. Among them: Pu, Am, Bk, Fm, No, Sg, Ds.