Class 11 Chemistry - BIHAR
Classification of Elements and Periodicity in Properties
The chapter 'Classification of Elements and Periodicity in Properties' for Class 11 Chemistry under the Bihar Board (BSEB) explores the systematic organization of elements in the periodic table. It builds upon early attempts like Dobereiner's triads and Newlands' law of octaves, leading to Mendeleev's periodic law and ultimately the modern periodic table based on atomic numbers. Students will learn about s, p, d, and f-block elements and periodic trends such as atomic radius, ionization enthalpy, electron gain enthalpy, and electronegativity. This foundational chapter carries significant weight in board exams and competitive tests like NEET and JEE.
Start Learning FreeKey Concepts
Modern Periodic Law
Physical and chemical properties of elements are periodic functions of their atomic numbers.
Atomic and Ionic Radii
The distance from the center of the nucleus to the outermost shell of electrons, which 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.
Electron Gain Enthalpy
The enthalpy change when an electron is added to a neutral gaseous atom to form a negative ion.
Electronegativity
The qualitative measure of the ability of an atom in a chemical compound to attract shared electrons to itself.
Important Formulas
Board Exam Info
In the Bihar Board (BSEB) Class 11 Chemistry examination, this chapter typically carries around 5 to 7 marks. Questions usually include objective (multiple-choice) questions on periodic trends, short-answer questions explaining why certain properties vary down a group or across a period, and reasons for anomalies such as the high electronegativity of fluorine or exception in electron gain enthalpy of noble gases.
Frequently Asked Questions
Why does atomic size decrease across a period?
Atomic size decreases across a period because the nuclear charge increases while electrons are added to the same shell, pulling the electron cloud closer to the nucleus.
Why is the electron gain enthalpy of fluorine less negative than that of chlorine?
Due to the small size of the fluorine atom, its compact electron density creates strong interelectronic repulsions, making it less favorable to add a new electron compared to chlorine.
What is the difference between electron gain enthalpy and electronegativity?
Electron gain enthalpy is the measurable energy change when an isolated gaseous atom accepts an electron, whereas electronegativity is a dimensionless, relative property representing an atom's tendency to attract shared electrons in a molecule.
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