Science NCERT Solutions Chapter 5 Periodic Classification of Elements Class 10 deals with the foundation of the periodic table and the positioning of the elements. Students studying for their Class 10 exams will learn about the classification of elements based on properties, such as whether the components in this table are metals or non-metals. It covers all major concepts in detail, allowing students to understand the ideas better. NCERT Periodic Classification of Elements Class 10 solutions the fifth chapter of the section, concentrates on topics such as Dobereiner's Triads, Newland's law of octaves, Mendeleev's periodic table, and the Modern Periodic table will help students grasp the periodic table. The chapter briefly examines the organization of elements in increasing atomic number order and chemical characteristics. These solutions consist of a series of direct questions and answers, followed by thorough explanations of several subtopics. Periodic Classification of Elements Class 10 Questions and Answers are very useful for getting good grades in tests and properly preparing you with all of the important concepts. These NCERT Solutions are valuable tools that can assist you not only in covering the full syllabus but also in providing an in-depth analysis of the subjects.
Limitations of Dobereiner’s classification:
| Mendeleev's periodic table|| Modern periodic table|
|1. Elements were arranged in increasing order of atomic masses.||1. Elements are arranged in increasing order of atomic numbers.|
|2. There are 8 groups.||2. There are 18 groups.|
|3. Each group is divided into subgroups a and b.||3. Groups are not divided into subgroups.|
|4. The group for noble gases was not present, as noble gases were not discovered at that time.||4. A separate group, i.e. group 18 is present for noble gases.|
|5. There was no place for isotopes.||5. This problem was rectified, as slots are determined on the basis of atomic number.|
The periodic table is a tabular representation of chemical elements in which components with comparable properties are found in the same vertical column or group. The periodic table is divided into sections based on atomic weight and valence electrons.
In 1817, Johann Wolfgang Döbereiner, a German scientist, identified certain groups with three elements each. As a result, he dubbed these groups "triads." The atomic mass was used to classify these elements. Döbereiner demonstrated that when the atomic masses of the three elements in a triad were listed in ascending order, the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.
For example, consider the triad of lithium (Li), sodium (Na), and potassium (K) having atomic masses of 6.9, 23.0, and 39.0, respectively.
In 1866, John Newlands, an English physicist, organized the known elements in ascending order of atomic mass. When atoms were placed in increasing atomic mass order, he discovered that every eighth element exhibited properties similar to the first. He linked it to the musical octaves. As a result, he dubbed it the "Law of Octaves."
The periodic table of Mendeleev is based on the physical and chemical properties of elements as well as their atomic masses. The elements were ordered according to their fundamental attribute, atomic mass, as well as chemical property similarity. The Periodic Table of Mendeléev has vertical columns called 'groups' and horizontal rows called 'periods.'
Henry Moseley demonstrated in 1913 that an element's atomic number is a more fundamental feature than its atomic mass. The atomic number (Z) of an element is equal to the number of protons in its nucleus.
The modern periodic table has 18 vertical columns called groups and 7 horizontal rows called periods. From left to right in the periodic table, the number of valence electrons in the elements present increases from 1 to 8. The number of shells remains constant when travelling from left to right. Each element in a periodic table group has the same number of valence electrons.
Q1. Explain the Periodic Table of Mendeleev in short.
Q2. Explain the demerits of Newland’s classification.
Answer: When heavier elements beyond Ca were organized according to Newland's law of octaves, this categorization failed. Noble gases were unknown at the time of this law. When noble gases such as Neon (Ne) between F and Na, and Argon (Ar) between Cl and K were discovered, they became the ninth element rather than the eighth.