Curious in Science

 Give reason questions. 1. It is necessary to classify elements. ​ Reason: There are 118 known elements, each possessing distinct physical and chemical properties. Classifying elements into groups based on their shared characteristics makes it systematic and significantly easier to study their behaviors, chemical trends, and reactions without having to memorize each element individually. ​2. Sodium and chlorine belong to different groups, but both have a valency of 1. ​ Reason: Valency is determined by the number of electrons an atom loses, gains, or shares to achieve a stable octet (outer electron shell): ​ Sodium ( \text{Na} ): Located in Group 1 with an electronic configuration of 2, 8, 1. It loses 1 electron to become stable, so its valency is 1. ​ Chlorine ( \text{Cl} ): Located in Group 17 with an electronic configuration of 2, 8, 7. It gains 1 electron to complete its shell, so its valency is also 1. ​Since both atoms transfer or share a single electron to ...

  Answers to Questions a. What is meant by classification of elements? Grouping elements by shared properties. Making the study of elements easy. b. State the modern periodic law. The physical and chemical properties of elements are a periodic function of their atomic numbers. c. How many periods are there in the modern periodic table? There are 7 horizontal rows called periods.   d. What are noble gases? Elements in Group 18 of the periodic table. They are unreactive and stable gases like helium and neon.   e. Why are alkali metals placed in Group 1? They have one valence electron in their outer shell. They share similar chemical properties.   f. Why do noble gases have zero valency? Their outermost electron shells are completely full. They do not need to lose, gain, or share electrons.

Test Your Concept multiple-choice questions: 1. Tick the correct alternative. a. Which of the following is the correct number of periods in the modern periodic table? ii. 7 b. Why do elements in the same group show similar chemical properties? iii. They have the same number of valence electrons. c. Which element will have the highest electronegativity in the second period? iv. Fluorine d. Which statement best explains why atomic size decreases across a period? i. Nuclear charge increases while shells remain the same. e. In which group does sodium belong to in the periodic table? iii. group 1 f. On which basis, are elements arranged in the modern periodic table? iii. atomic number g. Which of the following belong to the same period? (Looking at the table: A=2 (Helium, Period 1), B=10 (Neon, Period 2), C=5 (Boron, Period 2), D=11 (Sodium, Period 3)) ii. B, C h. What is the molecular weight of ammonia? (Nitrogen = 14 amu, Hydrogen = 1 amu × 3 = 3 amu. Total = 17 amu) i. 17 amu