Class 11 Chemistry - ODISHA
Classification of Elements and Periodicity in Properties
The chapter 'Classification of Elements and Periodicity in Properties' for Class 11 Odisha (BSE) students explores the systematic arrangement of elements in the periodic table. You will learn about early attempts like Dobereiner's Triads and Newlands' Law of Octaves, leading to Mendeleev's Periodic Table and the Modern Periodic Law. The chapter emphasizes periodic trends such as atomic radius, ionization enthalpy, electron gain enthalpy, and electronegativity. Mastering these concepts is crucial for board exams as they explain chemical reactivity, bonding, and form the foundation for inorganic chemistry.
Start Learning FreeKey Concepts
Modern Periodic Law
Properties of elements are a periodic function of their atomic numbers, which resolved anomalies present in Mendeleev's table based on atomic mass.
Atomic and Ionic Radius
Atomic size generally decreases across a period from left to right due to increasing effective nuclear charge and increases down a group due to the addition of new shells.
Ionization Enthalpy
The amount of energy required to remove an electron from an isolated gaseous atom in its ground state, which increases across a period and decreases down a group.
Electron Gain Enthalpy
The enthalpy change when an electron is added to an isolated gaseous atom, becoming more negative across a period and less negative down a group.
Electronegativity
The tendency of an atom to attract shared electrons in a covalent bond, increasing across a period and decreasing down a group.
Important Formulas
Board Exam Info
This chapter typically carries around 4 to 6 marks in the Odisha (BSE) Class 11 chemistry examinations. Common question types include 1-mark objective questions on periodic trends, short-answer reasoning questions (such as why the size of a cation is smaller than its parent atom), and definition-based questions on ionization enthalpy and electronegativity.
Frequently Asked Questions
Why is the size of a cation smaller than its neutral atom?
A cation is formed by the loss of one or more electrons, resulting in fewer electrons while the nuclear charge remains the same. This increases the pull of the nucleus on the remaining electrons, reducing the size.
Why does electron gain enthalpy become more negative across a period?
As you move across a period, atomic size decreases and nuclear charge increases, making it easier and more energetically favorable for the atom to accept an incoming electron.
What is the difference between electronegativity and electron gain enthalpy?
Electron gain enthalpy is the measurable energy released when a gaseous atom accepts an electron, whereas electronegativity is a dimensionless relative tendency of a bonded atom to attract shared electrons.
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