Long form of Periodic Table:
The long form of the periodic table is based on the periodic law, which states that the properties of elements vary periodically with their atomic number. The arrangement of elements in the periodic table is based on this principle, and is designed to reflect the patterns in the chemical and physical properties of the elements.
Disadvantages / Defects of long form of periodic table:
The long form of the periodic table is a tabular arrangement of chemical elements in order of their atomic number, electron configuration, and chemical properties. While the modern periodic table has been largely successful in organizing the elements and predicting their properties, there are a few defects in its structure that have been identified over the years. Here are some of the most significant defects of the long form of the periodic table:
1- Position of hydrogen:
Hydrogen is usually placed at the top of Group 1, along with the alkali metals, but its properties are quite different from those of the other elements in this group. The placement of hydrogen in IA group is justified only by the consideration of electronic configuration. Both hydrogen and alkali metals have one electron in the outermost subshell. But the properties of hydrogen and alkali metals are not similar.
2- Position of helium:
Helium is an inert gas that has a completely filled first energy level, with two electrons in its outermost shell. According to the Aufbau principle, the elements in the same period as helium should have similar electron configurations, but this is not the case. For example, the elements in the second period (lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon) have different electron configurations and chemical properties than helium.
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Chemically helium is an inert gas but since the other members of this group have valence shell configuration ns2, np6 against that of helium ( 1s2 ). A different place should be given to helium. The helium and alkaline earth metals have similar outermost shell electronic configuration as He ( 1s2 ), Alkaline earth metals. But due to different chemical properties of helium and alkaline earth metals this placement of helium is not possible.
3- Position of Lanthanides and Actinides:
The main body of the periodic table consists of the s, p, and d-block elements, which are organized into groups and periods based on their electron configurations. The s-block elements include the alkali metals and alkaline earth metals, the p-block elements include the nonmetals and metalloids, and the d-block elements include the transition metals. These elements have similar chemical and physical properties and follow the periodic trends in a predictable manner.
Reason:
The lanthanides (also known as rare earth elements) and actinides, on the other hand, have unique properties that do not follow the same patterns as the other elements. They have partially filled f-orbitals, which can result in different electron configurations and chemical properties. This makes it difficult to fit them into the main body of the periodic table in a way that reflects their unique properties while also maintaining the periodic trends observed in the other elements.
For this reason, the lanthanides and actinides are typically placed in a separate row below the main body of the periodic table, as mentioned earlier. This allows for a more compact and manageable table, while still acknowledging the unique properties of these elements.
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| Lanthanides |
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| Actinides |
4- Distribution of electrons:
This periodic table does not show the exact distribution of electrons among all the elements.
Why?
The periodic table is a graphical representation of the elements organized by their atomic number, electron configuration, and chemical properties. While the electron configuration of each element is important in determining its chemical properties and behavior, it is not practical or necessary to show the exact distribution of electrons for each element on the periodic table.
Reason:
The electronic configuration of an element describes the arrangement of electrons in its orbitals, which are regions of space around the nucleus where electrons are likely to be found. This configuration can be expressed using the notation 1s² 2s² 2p⁶ and so on, where the numbers and letters indicate the energy level and type of orbital in which the electrons are found. For example, the electron configuration of helium is 1s², indicating that it has two electrons in its first energy level.
However, showing the exact distribution of electrons for each element on the periodic table would be impractical because it would require a great deal of space and detail. Instead, the periodic table uses shorthand notation to indicate the electron configuration of each element, such as the use of abbreviated notation like [He] 2s² for the electron configuration of beryllium. This shorthand notation allows for a more concise and easy-to-use table while still conveying the essential information about the electron configuration of each element.
It’s worth noting that the electron configuration of an element is not fixed and can change depending on the chemical environment in which the element is found. For example, atoms of the same element can have different electron configurations when they are in different states of ionization or when they are in a compound with other elements. Despite this variability, the periodic table provides a useful framework for organizing and understanding the properties of the elements based on their electron configuration and other factors.