Class 11 Chemistry - WEST-BENGAL
Classification of Elements and Periodicity in Properties
The chapter 'Classification of Elements and Periodicity in Properties' in Class 11 Chemistry explores how elements are organized in the Modern Periodic Table based on their atomic numbers. It covers Dobereiner's Triads, Newlands' Octaves, Mendeleev's Periodic Table, and the Modern Periodic Law. Students learn about periodic trends in physical and chemical properties such as atomic radius, ionic radius, ionization enthalpy, electron gain enthalpy, and electronegativity. This chapter is fundamental for West Bengal (WBBSE) board exams, serving as a building block for chemical bonding and coordination chemistry, usually carrying around 4 to 6 marks in final evaluations.
Start Learning FreeKey Concepts
Modern Periodic Law
The physical and chemical properties of elements are periodic functions of their atomic numbers, not their atomic masses.
Atomic Radius
The distance from the centre of the nucleus to the outermost shell of electrons, which generally decreases across a period and increases down a group.
Ionization Enthalpy
The energy required to remove an electron from an isolated gaseous atom in its ground state, increasing across a period and decreasing down a group.
Electron Gain Enthalpy
The enthalpy change when an electron is added to a neutral gaseous atom to form an anion, becoming more negative across a period.
Electronegativity
The ability of an atom in a chemical compound to attract shared electrons towards itself, generally increasing from left to right across a period.
Important Formulas
Board Exam Info
In the West Bengal Council of Higher Secondary Education (WBBSE) Class 11 annual examinations, this chapter typically carries 4 to 6 marks. Questions usually include 1-mark multiple choice questions (MCQs), 2-mark short answer questions explaining periodic trends (like why atomic size decreases across a period), and reasoning-based questions regarding ionization energy or electronegativity.
Frequently Asked Questions
Why does atomic radius decrease across a period?
As we move from left to right across a period, the nuclear charge increases while electrons are added to the same shell. This creates a stronger pull from the nucleus, pulling the electron cloud closer and reducing the size.
What is the difference between electron gain enthalpy and electronegativity?
Electron gain enthalpy is the actual energy released when an isolated gaseous atom accepts an electron, whereas electronegativity is a relative tendency of a bonded atom to attract shared electrons in a molecule.
Why do noble gases have positive electron gain enthalpies?
Noble gases have completely filled stable electronic configurations (octet or duplet). Adding an extra electron requires energy input and is unfavorable, making their electron gain enthalpy positive.
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