Class 11 Chemistry - KERALA
Classification of Elements and Periodicity in Properties
This chapter explores how millions of chemical elements are organized into the Modern Periodic Table based on their electronic configurations. You will learn about Döbereiner's Triads, Newlands' Octaves, Mendeleev's table, and the Modern Periodic Law. Crucially, the chapter explains periodic trends in properties such as atomic radius, ionization enthalpy, electron gain enthalpy, and electronegativity across periods and down groups. Mastering this chapter is essential for Kerala SCERT board exams as it forms the foundational building block for inorganic chemistry, helping you predict chemical behavior and bonding in later chapters.
Start Learning FreeKey Concepts
Modern Periodic Law
The physical and chemical properties of elements are periodic functions of their atomic numbers.
Atomic Radius
The distance from the center of the nucleus to the outermost shell of electrons; it 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, generally increasing across a period.
Electron Gain Enthalpy
The enthalpy change when an electron is added to a gaseous atom, becoming more negative across a period and less negative down a group.
Electronegativity
The tendency of an atom in a covalent bond to attract shared pair electrons towards itself, peaking in the top-right of the periodic table.
Important Formulas
Board Exam Info
In the Kerala (SCERT) Class 11 Chemistry board examinations, this chapter typically carries around 4 to 6 marks. Common question types include conceptual reasoning questions on periodic trends (e.g., 'Why is the size of a cation smaller than its parent atom?'), defining periodic laws, and explaining anomalous behaviors of second-period elements.
Frequently Asked Questions
A cation is formed by the loss of one or more electrons, which decreases the number of shells or increases the effective nuclear charge, pulling the remaining electrons closer to the nucleus.
Why do noble gases have positive electron gain enthalpies?
Noble gases have fully filled, stable electronic configurations, making it energetically unfavorable to add an extra electron, thus requiring energy input.
What is the difference between electronegativity and electron gain enthalpy?
Electron gain enthalpy is the measured energy released when a gaseous atom accepts an electron, whereas electronegativity is a theoretical, qualitative property representing an atom's ability to attract shared electrons in a chemical bond.
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