Class 11 Chemistry - TELANGANA
Classification of Elements and Periodicity in Properties
The chapter 'Classification of Elements and Periodicity in Properties' in Class 11 Chemistry is foundational for understanding chemical behavior. It explores the historical development of the Periodic Table, starting from Dobereiner's Triads to Mendeleev's periodic law and the modern long form of the periodic table based on atomic numbers. Students learn how electronic configurations dictate chemical properties. Crucially, the chapter details periodic trends such as atomic radius, ionic radius, ionization enthalpy, electron gain enthalpy, and electronegativity across periods and down groups. Mastering this chapter is essential for scoring well in Telangana TSBSE board exams and competitive entrance tests.
Start Learning FreeKey Concepts
Modern Periodic Law
The physical and chemical properties of elements are a periodic function of their atomic numbers, resolving the anomalies of Mendeleev's table.
Atomic and Ionic Radius
Atomic radius decreases across a period due to increasing effective nuclear charge and increases down a group due to the addition of principal energy shells.
Ionization Enthalpy
The energy required to remove an electron from an isolated gaseous atom in its ground state; it generally increases across a period and decreases 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, with fluorine being the most electronegative element.
Important Formulas
Board Exam Info
In the Telangana (TSBSE) Class 11 Chemistry examinations, this chapter typically carries around 4 to 6 marks. Questions usually include very short answer questions (VSAQ - 2 marks) on periodic trends and definitions, and short answer questions (SAQ - 4 marks) explaining exceptions to ionization enthalpy or electron gain enthalpy.
Frequently Asked Questions
Why is the electron gain enthalpy of fluorine less negative than that of chlorine?
Due to the small size of the fluorine atom, the inter-electronic repulsions in its compact 2p orbital are relatively high, making the addition of a new electron slightly less favorable compared to chlorine.
What is screening effect or shielding effect?
The repulsion felt by valence electrons from the inner core electrons, which shields them from the full positive charge of the nucleus.
Why do noble gases have positive electron gain enthalpies?
Noble gases have stable, fully filled electronic configurations, so adding an extra electron requires energy rather than releasing it, resulting in endothermic (positive) values.
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