Periodic table
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The periodic table is a tabular arrangement all the known chemical elements, organized on the basis of their atomic number (number of protons in the nucleus), electron configurations, and recurring chemical properties.
Structure
The periodic table was invented and arranged by the Russian chemist Dmitry Ivanovich Mendeleyev (1834-1907).
Elements are presented in order of increasing atomic number, with each element being represented with a chemical symbol in each box. The standard form of the table consists of a grid of elements laid out in 18 columns and 7 rows, with a double row of elements below that.
A row of elements is called a period. There are 7 periods, each with different number of elements. Period 1 consists of only 2 elements, hydrogen and helium; period 2 and 3 both have 8 elements, period 4 and 5 have 18 elements each, while period 6 and 7 have 32 elements each.
A column of elements down the table is group. There are 18 groups in the standard periodic table. The old CAS model separated the groups in two types:the A (s and p block) and B (transitional metals). Elements in a group have electrons arranged in similar ways, which gives them similar chemical properties. The groups from the s and p block have their own name: Alkali metals (group I), alkaline earth metal (group II), pnictogens/pnictogens (group 15), chalcogens (group 16), halogens (group 17) and noble gases (group 18). The names given for groups 13 and 14 (icosagens and crystallogens) have not been accepted by IUPAC.
The periodic table can also be deconstructed into four rectangular blocks: the s-block to the left, the p-block to the right, the d-block in the middle, and the f-block below that.
