Chemistry(1st grade of high school): Theory

Classification of the elements (Periodic Table)

The groups, periods and their common characteristics:

A modern form of the periodic table is structured by horizontal rows (periods) and vertical columns (groups).

Periods:

Each horizontal row is occupied by elements whose atoms have "used" the same number of shells for the distribution of their electrons. These horizontal rows of the table are called periods.

Number in fact, of the period belongs the element, shows the number of layers in which its electrons are distributed.

In total there are seven periods.

The first period:

Contains only two elements, whose atoms have electrons only in the K shell.

The second and third periods:

Contains eight elements each, whose atoms have outer shells of L and M, respectively.

The fourth and fifth period:

They have eighteen elements each and their atoms have an outer layer of N and O, respectively.

The sixth:

Includes thirty-two elements with valence electrons (outer shell electrons) in the P .

The seventh period:

It currently includes twenty-six elements, (with the discovery of new artificial elements this number is constantly increasing) with valence electrons in the Q .

Along a period we have a decrease in the metallic character and an increase in the non-metallic character.

are Nonmetals at the far right of the periodic table and are separated from the rest of the elements, which are the metals.

The vertical columns of the periodic table are the groups and are occupied by elements with similar properties.

The groups are characterized by the Latin numbers I to VIII. They are distinguished in the main with the designation A and in the secondary with the designation B.

Elements belonging to the same main group have the same number of electrons in their outer shell, which is identified with the serial number of the group.

Group IA metals are called alkalis, group IIA alkaline earths and IIIA earths.

Elements that belong to secondary groups are called transition elements or transition. Group VIIA elements are called halogens and VIIIA noble gases.