Periodic Table Notes
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Periodic Table States that the physical & chemical properties of the elements are periodic functions of their atomic numbers. An arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same columns. Is organized by electron configuration. The periodic table is a tabular arrangement of chemical elements that are arranged by increasing atomic number and groups of elements according to recurring properties. The seven rows of the periodic table are called periods.
Periodic Table Notes
- In 1869, the Russian chemist Dmitri Mendeleyev published his great systematization called the periodic table.
- The periodic table is based on atomic masses and similar properties. In each row, the atomic masses increase toward the right. Each column contains a group of elements with similar chemical behavior.
- In the modern periodic table, each box contains four data. Besides the element name and symbol, the atomic mass is at the bottom, and the atomic number is at the top. The elements are arranged in order of increasing atomic number in horizontal rows called periods.
Features of Mendeleev’s Periodic Table
- Twelve horizontal rows, which were condensed to 7, are known as periods.
- Eight vertical columns are known as groups.
- Groups I to VII are subdivided into A and B subgroups.
- Group VIII doesn’t have any subgroups and contains three elements in each row.
- Elements in the same group exhibit similar properties.
Achievements of Mendeleev’s Periodic Table
- A systematic study of elements: Elements with similar properties were grouped together, which made the study of their chemical and physical properties easier.
- Correction of atomic masses: The placement of elements in Mendeleev’s periodic table helped in correcting the atomic masses of certain elements. For example, the atomic mass of beryllium was corrected from 13.5 to 9. Similarly, atomic masses of indium, gold, platinum etc., were also corrected.
- Prediction of properties of yet to be discovered elements: Eka-boron, eka-aluminum and eka-silicon were the names given to yet to be discovered elements. The properties of these elements could be predicted accurately from the elements that belonged to the same group. These elements, when discovered were named scandium, gallium, and germanium, respectively.
- Placement of noble gases: When discovered, they were placed easily in a new group called the zero groups of Mendeleev’s table, without disturbing the existing order.
Limitations of Mendeleev’s Periodic Table
- Position of hydrogen: Hydrogen resembles both, the alkali metals (IA) and the halogens (VIIA) in properties, so, Mendeleev could not justify its position.
- Position of isotopes: Atomic weight of isotopes differ, but, they were not placed in different positions in Mendeleev’s periodic table.
- Anomalous pairs of elements: Cobalt (Co) has higher atomic weights but was placed before Nickel (Ni) in the periodic table.
- Placement of like elements in different groups: Platinum (Pt) and Gold (Au) has similar properties but were placed in different groups.
- Cause of periodicity: He could not explain the cause of periodicity among the elements.
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