Classification of Elements and Periodicity in Properties

There are 118 elements known to us. It is tough to study such a large number of elements individually. To ease this problem, scientists researched a periodic pattern to organise their knowledge by categorising the elements. Not only that, it would rationalise elements but even predict new ones for undertaking further study.

Dmitri Mendeleev proposed the first periodic table of elements in 1869. He has arranged elements in groups and periods.

Periodic Table

The periodic table is the tabular array of chemical elements in order of increasing atomic number. It consists of 7 rows known as periods and eighteen columns known as columns. Metals are placed in group 1 to group 12 of the periodic table, whereas non-meals are placed in group 13 to group 17. To learn more about metals and non-metals, read metals and non-metals questions. It will enable you to review the topic and clear all your doubts.

Features of the Periodic table

  • There are 18 vertical columns in the periodic table known as groups.
  • There are 7 horizontal rows in the periodic table known as periods.
  • Light metals are placed in groups 1 or 2 of the periodic table.
  • Transition or heavy metals are placed in groups 3 to 12 of the periodic table.
  • Non-metals are placed in groups 13 to 17 of the periodic table.
  • Inert gases are placed in group 18 of the periodic table.
  • Elements of group 1 are known as alkali metals.
  • Elements of group 2 are known as alkaline earth metals.
  • Elements of group 3 to group 12 are known as transition elements.
  • Elements of group 15 are known as pnictogens.
  • Elements of group 16 are known as chalcogens.
  • Elements of group 17 are known as halogens.
  • Elements of group 18 are known as noble gases.

Cause of Periodicity

The periodic table of elements is based on the increasing atomic number, i.e. increasing protons in the atomic nucleus or increasing electrons in the neutral atom. The properties of elements depend on the number of electrons in the outermost shell. There is a repetition of a similar number of electrons in the outer energy shell of the atom. Thus they depict identical properties.

The elements of the same group have similar valence shell electronic configurations and exhibit similar properties. In contrast, the elements of the same period have an incrementally increasing number of electrons from left to the right and, therefore, have different properties.

Periodic trends

Periodic trends are observed in the atomic sizes, ionisation energy and valency of the elements. The atomic radii decrease left to right in a period because of an increase in effective nuclear charge. In contrast, atomic radii increase down the group because of an increase in the number of shells and a decrease in the amount of effective nuclear charge. Ionisation enthalpy typically increases on moving left to right across a period because of an increase in effective nuclear charge. In contrast, ionisation enthalpy decreases on moving down the group because of a decrease in effective nuclear charge. Valency also depicts some periodicity in the periodic table. Students can read the periodic table questions to understand the topic in-depth.

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