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FAQs on NCERT Textbook: Classification of Elements & Periodicity in Properties - Science & Technology for UPSC CSE

1. What is the periodic table and why is it important?
Ans. The periodic table is a tabular arrangement of chemical elements based on their atomic number, electron configuration, and recurring chemical properties. It is an essential tool in chemistry as it provides a systematic way to organize and categorize elements based on their properties, allowing scientists to predict and understand the behavior of different elements and compounds.
2. How are elements classified in the periodic table?
Ans. Elements in the periodic table are classified based on their atomic number, which represents the number of protons in the nucleus of an atom. The elements are arranged in periods (rows) and groups (columns) on the basis of their similar chemical properties and electronic configurations. Elements within the same group share similar characteristics and tend to exhibit similar chemical reactions.
3. What are the main trends observed in the periodic table?
Ans. The periodic table exhibits several trends or patterns. Some of the main trends include: - Atomic size: Atomic size generally decreases from left to right across a period and increases from top to bottom within a group. - Ionization energy: Ionization energy tends to increase from left to right across a period and decrease from top to bottom within a group. - Electronegativity: Electronegativity generally increases from left to right across a period and decreases from top to bottom within a group. - Metallic character: Metallic character tends to decrease from left to right across a period and increase from top to bottom within a group.
4. How are elements arranged in periods and groups in the periodic table?
Ans. The periodic table consists of periods (rows) and groups (columns). Elements in the same period have the same number of electron shells or energy levels. Elements in the same group have similar outer electron configurations and exhibit similar chemical properties. For example, elements in Group 1 (alkali metals) have one valence electron, while elements in Group 17 (halogens) have seven valence electrons.
5. How can the periodic table be used to predict element properties?
Ans. The periodic table allows scientists to make predictions about the properties of elements. By examining an element's position in the periodic table, one can infer its atomic size, ionization energy, electronegativity, and other properties. For example, elements in the same group tend to have similar chemical reactivity and form similar types of compounds. This predictive power of the periodic table is crucial in understanding and designing chemical reactions, identifying unknown elements, and exploring new areas of research in chemistry.
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