Class 11 Chemistry - HARYANA
Classification of Elements and Periodicity in Properties
The chapter 'Classification of Elements and Periodicity in Properties' in Class 11 Chemistry builds the foundational understanding of how the modern periodic table is organized based on atomic numbers and electronic configurations. Students explore periodic trends such as atomic radius, ionic radius, ionization enthalpy, electron gain enthalpy, and electronegativity. Mastering this chapter is crucial for Haryana Board (BSEH) exams as it directly links atomic structure with chemical reactivity, frequently appearing in both objective and descriptive questions. A strong grasp of these periodic trends makes predicting the behavior of elements across periods and groups much easier.
Start Learning FreeKey Concepts
Modern Periodic Law
Properties of elements are a periodic function of their atomic numbers, which resolved many anomalies of Mendeleev's table based on atomic masses.
Atomic and Ionic Radius
Atomic radius generally decreases across a period due to increased effective nuclear charge and increases down a group due to the addition of new shell levels.
Ionization Enthalpy
It is the energy required to remove an electron from an isolated gaseous atom, generally increasing across a period and decreasing down a group.
Electron Gain Enthalpy
The enthalpy change when an electron is added to a neutral gaseous atom, becoming more negative across a period and less negative down a group.
Electronegativity
The ability of an atom in a chemical compound to attract shared electrons, increasing across a period and decreasing down a group.
Important Formulas
Board Exam Info
In the Haryana Board (BSEH) Class 11 Chemistry examination, this chapter typically carries around 4 to 6 marks. Common question types include 1-mark multiple-choice questions on periodic trends, short-answer questions explaining why ionization energy drops or increases, and reasoning questions comparing sizes of atoms and their corresponding ions.
Frequently Asked Questions
A cation is formed by the loss of one or more electrons, which decreases the repulsion among remaining electrons while the nuclear charge remains the same, pulling the electron cloud closer to the nucleus.
Noble gases have fully filled stable electronic configurations, so adding an extra electron requires energy rather than releasing it, resulting in a positive electron gain enthalpy.
Metallic character decreases across a period from left to right because electronegativity and nuclear charge increase, and it increases down a group as atomic size increases and valence electrons are more easily lost.
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