Class 9 Science - ICSE-CHEMISTRY
The Periodic Table
The chapter 'The Periodic Table' in Class 9 ICSE Chemistry introduces students to the systematic arrangement of elements based on the Modern Periodic Law. Students explore Dobereiner's Triads, Newlands' Octaves, and Mendeleev's Periodic Table to understand how historical attempts paved the way for Henry Moseley's modern atomic number-based table. This chapter covers periods, groups, and the classification of elements into metals, non-metals, metalloids, and noble gases. Mastering this chapter is crucial for board exams as it builds the foundational understanding of chemical bonding, valency, and periodic properties needed for Class 10 ICSE Chemistry.
Start Learning FreeKey Concepts
Dobereiner's Triads
A group of three elements arranged in increasing order of atomic mass where the atomic mass of the middle element is approximately the arithmetic mean of the first and third elements.
Newlands' Law of Octaves
States that when elements are arranged in increasing order of atomic mass, every eighth element has properties similar to the first, much like the notes of music.
Mendeleev's Periodic Law
States that the physical and chemical properties of elements are a periodic function of their atomic masses.
Modern Periodic Law
States that the physical and chemical properties of elements are a periodic function of their atomic numbers, formulated by Henry Moseley.
Periods and Groups
The horizontal rows in the periodic table are called periods (7 in total), and the vertical columns are called groups (18 in total).
Important Formulas
Board Exam Info
In ICSE Chemistry (Class 9), this chapter typically carries around 6 to 8 marks in the final exams. Common question types include defining periodic laws, stating merits and demerits of Mendeleev's table, identifying positions of elements based on atomic numbers, and differentiating between groups and periods.
Frequently Asked Questions
Why is the Modern Periodic Table based on atomic number instead of atomic mass?
Atomic number represents the number of protons or electrons in an atom, which is a more fundamental property than atomic mass and successfully resolves anomalies like the position of isotopes.
What are alkali metals and halogens?
Alkali metals are reactive metals found in Group 1 of the periodic table, while halogens are reactive non-metals found in Group 17.
How do you find the group and period of an element from its electronic configuration?
The number of shells gives the period number, and the number of valence electrons determines the group number (for groups 1, 2, and 13 to 18, valence electrons plus 10).
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