(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) (i) All the elements of a group have similar chemical properties because they have the same number of valence electrons in their outermost shell.
(ii) All the elements of a period have different chemical properties because they have different numbers of valence electrons in their atoms.
(b) As the atomic number increases in a period from left to right, the size of atoms goes on decreasing and the order of atomic numbers of elements will be X < Z < Y.
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- The atomic radii of the first group elements are given below :Group-I elementAtomic Radii (pm)Na86K231Rb244Cs282State the reason behind the observed trend in the above elements.
- (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:
- 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?
- The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called as? Give one example of such a set of elements.
- The atomic masses of three elements X, Y and Z having similar chemical properties are 7, 23 and 39 respectively.(a) Calculate the average atomic mass of elements X and Z. (b) How does the average atomic mass of elements X and Z compare with the atomic mass of element Y? (c) Which law of classification of elements is illustrated by this example? (d) What could the elements X, Y and Z be? (e) Give another example of a set of elements which can be classified according to this law.
- The atomic numbers of the three elements X, Y and Z are 2, 6 and 10 respectively.(i) Which two elements belong to the same group? (ii) Which two elements belong to the same period? Give reasons for your choice.
- How do the atomic radii of elements change as we go from left to right in a period of the periodic table?
- (a) What is a period in a periodic table? How do atomic structures (electron arrangements) change in a period with increase in atomic numbers from left to right?(b) How do the following change on going from left to right in a period of the periodic table? (i) Chemical reactivity of elements (ii) Nature of oxides of elements Give examples in support of your answer.
- (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?
- (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.
- 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.
- (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) In this ladder (Figure 5.2) symbols of elements are jumbled up. Rearrange these symbols of elements in the increasing order of their atomic number in the Periodic Table.(b) Arrange them in the order of their group also."
- (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?
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