How many of the following have 10 electrons: O2-, O, Al3+, Al, F, F-, Mg2+, Mg, N-3
Solution and Explanation
Correct answer: 5 (O2-, Al3+, F-, Mg2+, N3-)
A negative sign means more electrons, and a positive sign means a lack of electrons.
- N3- with atomic number 7 has 7 + 3 = 10 electrons
- O2- with atomic number 8 has 8 + 2 = 10 electrons
- F- with atomic number 9 has 9 + 1 = 10 electrons
- Na+ with atomic number 11 has 11 - 1 = 10 electrons
- Mg2+ with atomic number 12 has 12 - 2 = 10 electrons
- Al3+ with atomic number 13 has 13 - 3 = 10 electrons
Since all these ions have 10 electrons in their shell, therefore, these are iso-electronic species.
The more positive the charge, the smaller the ionic radius. Remember that negative means adding electrons.
These electrons go in the outermost shells.
Top Questions on Classification of elements and periodicity in properties
Match List I with List II.
- BITSAT - 2024
- Chemistry
- Classification of elements and periodicity in properties
In which of the following reactions of H$_2$O$_2$ acts as an oxidizing agent (either in acidic, alkaline, or neutral medium)?
% Given Reactions
(i) \( 2Fe^{2+} + H_2O_2 \rightarrow \)
(ii) \( 2MnO_4^- + 6H^+ + 5H_2O_2 \rightarrow \)
(iii) \( I_2 + H_2O_2 + 2OH^- \rightarrow \)
(iv) \( Mn^{2+} + H_2O_2 \rightarrow \)
- BITSAT - 2024
- Chemistry
- Classification of elements and periodicity in properties
- A metalloid is:
- KCET - 2024
- Chemistry
- Classification of elements and periodicity in properties
- A pair of isoelectronic species having a bond order of one is:
- KCET - 2024
- Chemistry
- Classification of elements and periodicity in properties
- Which of the following statements related to lanthanoids is incorrect?
- KCET - 2024
- Chemistry
- Classification of elements and periodicity in properties
Notes on Classification of elements and periodicity in properties
Concepts Used:
Classification of Elements & Periodicity in Properties
Since many elements were being discovered in the 19th century and the study of these elements individually was proving difficult, classification of elements was made necessary.
Classification by Johann Dobereiner - German chemist Johann Dobereiner classified certain elements on the basis of their similar properties in the groups of continuing - three elements each. These groups were called ‘triads’. In every triad, the atomic weight of the middle element was equal to the average of the atomic weights of the first and third elements.
Newlands Law of Octaves - The elements were arranged in increasing order of their atomic weights and found that every 8th element shows similarity with the 1st element.
Mendeleev’s Periodic Table - The arrangement of all 63 elements in rows or columns in order of their atomic weight was made by Mendeleev. He left some space for corresponding elements in his periodic table which were not even discovered till then. Although he predicted the properties of those elements through his periodic classification of elements.
Modern Periodic Law - The properties of the elements of the modern periodic law are periodic functions of their atomic numbers.