(a) Explain why, the first period of the modern periodic table has only two elements whereas second period has eight elements
(b) Why do elements in the same group show similar properties but the elements in different groups show different properties?
(c) For each of the following triads, name the element with the characteristics specified below:

Elements	Least atomic radius	Chemically least reactive
(i) F AcademicChemistryNCERTClass 10 (a) The 1st period has two elements because the 1st electron shell of an atom can take a maximum of two electrons only. The 2nd period of the periodic table has 8 electrons because the maximum no. of electrons that can accumulate in the 2nd shell of an atom is 8.  (b) The elements in the same group show similar properties because they have similar electronic configurations whereas the elements of different groups have different electronic configurations due to which they show different properties. (c)  Elements Least atomic radius Chemically least reactive (i) F, Cl, Br F Br (ii) Li, Na, K Li Li (d) Fluorine and chlorine have been placed in the same group because both of them have 7 valence electrons.   (e) Merits of the modern periodic table are given below: (i) The modern periodic table is based on the atomic numbers of elements which is the most fundamental property of elements. (ii) It helps us to understand why elements in a group show similar properties but elements in different groups show different properties. (iii) It explains the reasons for the periodicity in properties of elements. (iv) It tells us why the properties of elements are repeated after 2, 8, 18, and 32 elements. Tutorialspoint Updated on: 10-Oct-2022 37 Views Related Articles What is periodicity in properties of elements with reference to the Modern Periodic Table? Why do all the elements of the same group have similar properties? How does the tendency of elements to gain electrons change as we move from left to right in a period? State the reason of this change? (a) Explain why:(i) All the elements of a group have similar chemical properties. (ii) All the elements of a period have different chemical properties. (b) The atomic radii of three elements X, Y, and Z of a period of the periodic table are 186 pm; 104 pm, and 143 pm respectively. Giving a reason, arrange these elements in the increasing order of atomic numbers in the period. (a) What is the main characteristic of the last elements in the periods of the periodic table? What is the general name of such elements?(b) What is the number of elements in: (a) 1st period, and (b) 3rd period, of the modern periodic table? (a) What is a group in the periodic table? In which part of a group would you separately expect the elements to have (i) the greatest metallic character (ii) the largest atomic size?(b) In what respects do the properties of group 1 elements differ from those of group 17 elements? Explain with examples by taking one element from each group. (c) From the standpoint of atomic structure, what determines which element will be the first and which the last in a period of the periodic table? (d) Explain why, the properties of elements are repeated after 2, 8, 18, and 32 elements in the periodic table. (e) What are the advantages of the periodic table? Given below are some elements of the modern periodic table: 4Be, 9Fe, 14Si, 19K, 20Cai. Select the element that has one electron in the outermost shell and write its electronic configuration.ii. Select two elements that belong to the same group. Give reasons for your answer.iii. Select two elements that belong to the same period. Which one of the two has bigger atomic size? Consider the following elements:Na, Ca, Al, K, Mg, Li (a) Which of these elements belong to the same period of the periodic table? (b) Which of these elements belong to the same group of the periodic table? Mendeleev predicted the existence of certain elements not known at that time and named two of them as eka-aluminium, and eka-silicon.(a) Name the element which has taken the place of (i) eka-aluminium, and (ii) eka-silicon (b) Mention the period/periods of these elements in the modern periodic table. (c) Write the group/ groups of these elements in the modern periodic table. (d) Classify these elements as metals, non-metals or metalloids. (e) How many valence electrons are present in the atoms of each of these elements? Fill in the following blanks with suitable words:(a) The basis for modern periodic table is ______. (b) The horizontal rows in a periodic table are called ______. (c) Group 1 elements are called ______. (d) Group 17 elements are known as ______. (e) Group 18 elements are called ______. (f) According to Newlands’ classification of elements, the properties of sulphur are similar to those of oxygen because sulphur is the ______ element starting from oxygen. State whether the following statement are true or false:(a) Newlands divided the elements into horizontal rows of eight element each. (b) According to Mendeleev’s periodic law, the properties of elements are a periodic function of their atomic numbers. (c) The elements in a group have consecutive atomic numbers. Given below are some elements of the modern periodic table. Atomic number of the element is given in parentheses. A (4), B (9), C (14), D(19), E(20)(a) Select the element that has one electron in the outermost shell. Also, write the electronic configuration of this element.(b) Which two elements amongst these belong to the same group? Give reasons for your answer.(c) Which two elements amongst these belong to the same period? Which one of the two has bigger atomic radius? Atomic number of a few elements are given below 10, 20, 7, 14(a) Identify the elements(b) Identify the Group number of these elements in the Periodic Table(c) Identify the Periods of these elements in the Periodic Table(d) What would be the electronic configuration for each of these elements?(e) Determine the valency of these elements. (a) What is meant by (i) a group, and (ii) a period, in a periodic table?(b) How many periods and groups are there in the long form of periodic table? (c) Give two examples each of (i) group 1 elements (ii) group 17 elements (iii) group 18 elements. In the modern periodic table, the element calcium (atomic number = 20) is surrounded by elements with atomic numbers 12, 19, 21, and 38. Which of these elements has physical and chemical properties resembling those of calcium and why? (a) How does the electropositive character of elements change on going down in a group of the periodic table?(b) State how the valency of elements varies (i) in a group, and (ii) in a period, of the periodic table. Define the Periodic Table with elements name. Kickstart Your Career Get certified by completing the course Get Started Print Page Previous Next Advertisements × To Continue Learning Please Login Login with Google