
How can you predict the group, period and block of an element? Explain with examples.
Answer
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Hint: All elements have a characteristic property known as the atomic number. The atomic number of an element represents the number of electrons or protons present in the atom of the element. On the other hand, Aufbau’s Principle helps in determining the order in which the electron orbitals get filled. Using both these concepts, we can determine the electronic configuration of the given element.
Complete step by step answer:
Note:
and so on.
Complete step by step answer:
-When we have filled all the electrons, the orbital in which the last electron is in, represents the block in which the element is placed.
-Now, to determine the period in which the element is placed, we need to look at the principal quantum number of the valence electron.
-To determine the group, we need to understand some rules:
1.If the element is in s block, then the group number is equal to the number of valence electrons.
2.If the element is in the p block, then the number of the group can be determined by the formula: (number of valence electrons + 10).
3.If the element is in the d block, then the number of the group can be determined by the formula: [number of electrons in (n-1) d subshell] + (number of electrons in (n) s subshell).
4.If the element is in the f block, then the number of the group is always 3.
-Let us solve an example to understand these concepts. Let us consider Iron:
The atomic number of iron is 26. Hence the electronic configuration is given as .
Since the valence electron enters into the 3d subshell, the given element belongs to the d block.
The principal quantum number of the valence electron of Fe is 3. Hence, it belongs to the 3rd period.
Since iron belongs to d block, its group number can be calculated by using:
[number of electrons in (n-1) d subshell] + (number of electrons in (n) s subshell)
Hence, iron belongs to the 8th group.
According to Aufbau’s principle, the order in which the orbitals fill up is as follows:
Each orbital has a fixed capacity for the maximum number of electrons accommodated, s-orbitals have the capacity of 2 electrons, while p orbitals have the capacity for 6 electrons, d orbitals have the capacity for 10 electrons and f orbitals have the capacity for 14 electrons. One we get the atomic number of the element; we can start filling the orbitals in the order mentioned by the Aufbau principle.
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