Download Periodic classificatiion of elements

How many elements are known at present?
A. 114 elements.
2. How many elements are known around 1800?
A. 30 elements.
3. What is the earliest attempt of classification?
A. The earliest attempt of classification is grouping the then known elements as metals and
non-metals.
4. In which year Dobereiner classified elements into groups?
A. 1817.
5. What are traids?
A. Dobereiner classified elements, three elements in each group. So he called these groups
as traids.
6. How are elements arranged in a traid and what is the importance of traid in his
classification?
A. Elements are arranged in the order of increasing atomic masses. The atomic mass of
middle element was roughly the average of the atomic masses of the other two elements
7. In which year did Newlands classified elements?
A. 1866.
8. What is the main feature of Newlands classification?
A. In octaves classification, the properties of the first and the eighth element are same.
9. How did Newland compared his classification?
A. In this Law of octaves (every eight note is equal to first note].
10. What are the limitations of Newlands classification?
A. Limitations of Newlands classification are
a. Newland’s law was applicable only upto calcium.
1. He assumed that only 56 elements existed in nature and no more elements would be
discovered in future.
2. Cobalt [Co] and Nickel [Ni] are placed in the same slot and these are placed in the same
column as Fluorine [F], Chlorine [Cl] and Bromine [Br] which are different in
properties. Iron [Fe] which resembles Cobalt [Co] and Nickel [Ni] in properties has
been placed far away from these elements. Thus, they worked for lighter elements only.
11. Who is the most important contributor to the early development of periodic table?
A. Dmitri Ivanovich Mendeleev.
12. How many elements were known during the periodic classification of Mendeleev?
A. 63 elements.
13. What is the basic property treated by Mendeleev in classification?
A. The formula of the hydrides and oxides formed by and element is treated as one of the
basic properties of classification.
14. What is the periodic law formulated by Mendeleev?
A. The properties of elements are the periodic function of their atomic masses.
15. What are groups?
A. Vertical columns in periodic table are called groups.
16. What are periods?
A. Horizontal rows in periodic table are called periods.
17. What are the achievements of Mendeleev’s periodic table?
A. Achievements of Mendeleev’s periodic table
1. Mendeleev left some gaps in periodic table. Due to this he boldly predicted the existence
of some other elements.
2. When inert gases were discovered they found place in the Mendeleev periodic table.
18. What are the imitations of Mendeleev periodic table?
A. Limitations of Mendeleev periodic table
1. Mendeleev could not assign a correct position to hydrogen in his table.
2. Isotopes of all elements posed a challenge to his periodic law.
3. Atomic masses do not increase in a regular manner in going from one element to the
next.
19. Who showed that atomic number is more fundamental than atomic mass in
classification?
A. Henry Moseley [in1913].
20. What is modern periodic law?
A. Modern periodic law states ‘properties of elements are a periodic function of their
atomic number’.
21. How can we get modern periodic table?
A. Elements when arranged in order of increasing atomic number, lead us to the
classification known as Modern periodic table.
22. How many groups are there in modern periodic table?
A. 18 groups.
23. How many periods are there in modern periodic table?
A. 7 periods.
24. What do groups in a modern periodic table signify?
A. Groups in periodic table signify an identical outer shell electronic configuration.
25. When do number of shells increase in a group?
A. The number of shells increases as we go down the group.
26. What happens to valency electrons when we move from left to right in a period?
A. Valence electrons increase by one unit as we move from left to right in a period.
27. Write the formula on which maximum number of electrons in a shell depends?
A. 2n2 (where n is number of given shell from nucleus).
28. What happens to atomic size when we move from left to right in a period?
A. Atomic size decreases when we move from left to right in a period.
29. Why does atomic size decreases on moving from left to right in a period?
A. Atomic size decreases on moving from left to right in a period because an increase in
nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of
the atom.
30. What happens to the atomic size as we go down a group?
A. Atomic size increases as we go down a group.
31. Why does atomic size increase on moving from up to down in a group?
A. Atomic size increases on moving from up to down in a group because new shells are
being added as we go down the group. This increases the distance between the outermost
electrons and the nucleus so that the atomic size increases in spite of the increase in nuclear
charge.
32. Give some examples of metalloids.
A. Boron [B], Silicon [Si], Germanium [Ge], Arsenic [As], Antimony, Tellurium and
Polonium.
33. What is a metalloid?
A. The element which exibhits both the properties of metals and non-metals is called
metalloid.
34. What happens to metallic character on moving from left to right?
A. Metallic character decreases on moving from left to right.
35. What of these are electropositive-metals or non-metals?
A. Metals.
36. What happens to metallic character on moving down a group?
A. Metallic character increases on moving down a group.
37. Why does the tendency to lose electrons decrease on moving from left to right in a
period?
A. The tendency to lose electrons decreases on moving from left to right in a period because
the effective nuclear charge acting on the valence shell electrons increases across a period,
the tendency to lose electrons will decrease.
38. Why tendency to lose electrons increases on moving down in a group?
A. Down the group the effective nuclear charge experience by valence electrons is
decreasing because the outermost electrons are farther away from the nucleus. Therefore,
these can be lost easily.
39. What are electronegative-metals or non-metals?
A. Non-metals.
40. In which form is matter present?
A. Matter is present in the form of elements, compounds and mixtures.
41. What type of atoms does an element contain?
A. Elements contain atoms of only one type.
42. Why do scientists started looking for some pattern in their properties, on the basis of
which they could study such a large no. of elements with ease?
A. As different elements were being discovered, scientists, gathered more and more
information about the properties of elements. They started looking for some pattern in
their properties, on the basis of which they could study such a large number of elements
with ease.
43. To which country does Mendeleev belong to?
A. Mendeleev belongs to Russia.
44. In which year was Mendeleev’s periodic table published n a Germany journal?
A. 1872.
45. What is R in RO, RH etc?
A. R is used to represent any of the elements in the group.
46. Why are inert gases discovered late?
A. Inert gases are discovered very late because they are very inert and present in extremely
low concentrations in our atmosphere.
47. Why is no fixed position be given to hydrogen in the periodic table?
A. Like alkali metals, hydrogen combines with halogens, oxygen and sulphur to form
compounds having same formula.
On the otherhand, just like halogens, hydrogen also exists as diatomic molecules and it
combines with metals and non-metals to form covalent compounds.
48. In which year Henery Moseley showed that atomic number is a more fundamental
property than atomic mass of element in classification?
A. 1913.
49. What is common in a period of elements?
A. All elements in a period contain same number of shells.
50. What is common in a group of elements?
A. All elements in a group have the same number of valence electrons.
51. What tells about the chemical reactivity of an element in the periodic table?
A. The position of an element in the periodic table tells us about its chemical reactivity.
52. How is the valency of an element determined?
A. The valency of an element in determined by the number of valence electrons present in
the outermost shell of its atom.
53. What is atomic size?
A. The term atomic size refers to the radius of an atom.
54. How is the atomic size visualized?
A. The atomic size may be visualized as the distance between the center of the nucleus and
the outermost shell of an isolated atom.
55. What is the atomic size of hydrogen atom?
A. 37pm.
56. Express picometer in metre.
A. 1picometre = 10-12metre.
57. What is the nature of metallic oxides?
A. Basic.
58. What is the nature of non-metallic oxides?
A. Acidic.
59. Where are non-metals found in the periodic table?
A. Non-metals are found on the right-hand side of the periodic table towards the top.
60. What is the basis for the classification of elements?
A. Elements are classified on the basis of similarities in their properties.
61. Which properties periodicity is shown by elements in classification?
A. Elements arranged show periodicity of properties including atomic size, valency and
metallic and non-metallic character.