Class 11 Chemistry - ISC
Classification of Elements and Periodicity in Properties
The chapter Classification of Elements and Periodicity in Properties forms the foundation of inorganic chemistry for Class 11 ISC students. It explores how elements are organized in the Modern Periodic Table based on their electronic configurations and atomic numbers. You will study periodic trends such as atomic radius, ionization enthalpy, electron gain enthalpy, and electronegativity, which help predict element behavior. Mastering this chapter is crucial for board exams as it explains chemical bonding and reactivity, frequently appearing in both objective and descriptive ISC questions.
Start Learning FreeKey Concepts
Modern Periodic Law
Properties of elements are a periodic function of their atomic numbers, resolving anomalies present in Mendeleev's mass-based table.
Atomic and Ionic Radii
Atomic radius decreases across a period due to increasing effective nuclear charge and increases down a group due to the addition of new electron shells.
Ionization Enthalpy
The energy required to remove an electron from an isolated gaseous atom; it increases across a period and decreases down a group.
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 to attract shared electrons in a covalent bond, with Fluorine being the most electronegative element.
Important Formulas
Board Exam Info
In the ISC Class 11 Chemistry examination, this chapter typically carries around 4 to 6 marks. Questions frequently include reasoning-type problems based on periodic trends (such as comparing sizes of isoelectronic species), defining periodic laws, and explaining anomalous behaviors like why the electron gain enthalpy of fluorine is less negative than that of chlorine.
Frequently Asked Questions
Noble gases are measured using van der Waals radius, which is non-bonded and naturally larger than the covalent radius used for halogens.
Noble gases are measured using van der Waals radius, which accounts for non-bonded atoms and is larger than covalent radii.
What are isoelectronic species and how do we compare their sizes?
Isoelectronic species have the same number of electrons. For these, size decreases as nuclear charge (atomic number) increases because a higher positive charge pulls the electron cloud closer.
Why does electron gain enthalpy become less negative down a group?
As you go down a group, atomic size increases and the incoming electron is added further from the nucleus, reducing the attractive force and making energy release less favorable.
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