Q.1. 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.
Q.2. Elements have been arranged in the following sequence on the basis of their increasing atomic masses.
F, Na, Mg, Al, Si, P, S, Cl, Ar, K
(a) Pick two sets of elements which have similar properties.
(b) The given sequence represents which law of classification of elements?
(b) Newland’s Law of Octaves
Q.3. Can the following groups of elements be classified as Dobereiner’s triad?
(a) Na, Si, Cl
(b) Be, Mg, Ca
Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40. Explain by giving reason. [Delhi 2019]
(a) No, it is because these three elements do not resemble in their properties although atomic mass of Si is nearly average of the atomic masses of Na and Cl.
(b) Yes, because these elements resemble with each other and the atomic mass of Mg is nearly equal to average of the atomic masses of Be and Ca.
Q.4. In Mendeleev’s Periodic Table, the elements were arranged in the increasing order of their atomic masses. However, cobalt with atomic mass of 58.93 amu was placed before nickel having an atomic mass of 58.71 amu. Give reason for the same.
Ans. It was because elements with similar properties were grouped together, and increasing order of atomic mass could not be followed.
Q.5. “Hydrogen occupies a unique position in the Modern Periodic Table”. Justify the statement.
Ans. Hydrogen resembles with both group 1 (Alkali metals) and group 17 (Halogens). Therefore, it occupies a unique position in the Modern Periodic Table.
Q.6. Write the formula of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev.
Q.7. Three elements A, B and C have 3, 4 and 2 electrons respectively in their outermost shell. Give the group number to which they belong in the Modern Periodic Table. Also, give their valencies.
Q.8. If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride?
Q.9. Compare the radii of two species X and Y. Give reasons for your answer.
(a) X has 12 protons and 12 electrons
(b) Y has 12 protons and 10 electrons
Q.10. Arrange the following elements in increasing order of their atomic radii.
(a) Li, Be, F, N
(b) Cl, At, Br, I
(a) F < N < Be < Li, is increasing order of atomic size because atomic size decreases along a period from left to right.
(b) Cl < Br < I < At, is increasing order of atomic size because atomic size increases down the group due to increase in the number of shells.
Q.11. Identify and name the metals out of the following elements whose electronic configurations are given below.
(a) 2, 8, 2
(b) 2, 8, 1
(c) 2, 8, 7
(d) 2, 1
Q.12. Arrange the following elements in the increasing order of their metallic character: Mg, Ca, K, Ge, Ga.
Q.13. Identify the elements with the following property and arrange them in increasing order of their reactivity.
(a) An element which is a soft and reactive metal.
(b) The metal which is an important constituent of limestone.
(c) The metal which exists in liquid state at room temperature.
(a) Na (Sodium) or K (Potassium)
(b) Ca (Calcium)
(c) Hg (Mercury)
Reactivity order: Hg < Ca < Na < K.
Q.14. Properties of the elements are given below. Where would you locate the following elements in the periodic table?
(a) A soft metal stored under kerosene.
(b) An element with variable (more than one) valency stored underwater.
(c) An element which is tetravalent and forms the basis of organic chemistry.
(d) An element which is an inert gas with atomic number 2.
(e) An element whose thin oxide layer is used to make other elements corrosion-resistant by the process of “anodising”.
(a) Group 1 and period 3 or group 1 and period 4 (Sodium or Potassium).
(b) Group 15 and period 3 (Phosphorus).
(c) Group 14 and period 2 (Carbon).
(d) Group 18 and period 1 (Helium).
(e) Group 13 and period 3 (Aluminium).
Q.15. An element is placed in 2nd Group and 3rd Period of the Periodic Table burns in the presence of oxygen to form a basic oxide.
(a) Identify the element.
(b) Write the electronic configuration.
(c) Write the balanced equation when it burns in the presence of air.
(d) Write a balanced equation when this oxide is dissolved in water.
(e) Draw the electron dot structure for the formation of this oxide.
Q.16. An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide.
(a) Where in the periodic table are elements X and Y placed?
(b) Classify X and Y as metal(s), non-metal(s) or metalloid(s)
(c) What will be the nature of oxide of element Y? Identify the nature of bonding in the compound formed.
(d) Draw the electron dot structure of the divalent halide.
(a) ‘X’ is in group 17 and 3rd period, ‘Y’ is in group 2 and 4th period.
(b) ‘X’ is non-metal, and 'Y’ is a metal.
(c) ‘Y’ forms basic oxide. It has ionic bonding in the oxide formed.
(d) is electron dot structure. YX2 is the formula.
Q.17. 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.
Q.18. Mendeleev predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium.
(a) Name the elements which have taken the place of these elements.
(b) Mention the group and the period of these elements in the Modern Periodic Table.
(e) Classify these elements as metals, non-metals or metalloids.
(d) How many valence electrons are present in each one of them?
(c) Ge is metalloid, Ga is metal.
(d) Ge has 4 valence electrons, and Ga has 3 valence electrons.
Q.19. (i) Electropositive nature of the elements(s) increases down the group and decreases across the period.
(ii) Electronegativity of the element decreases down the group and increases across the period.
(iii) Atomic size increases down the group and decreases across a period (left to right).
(iv) Metallic character increases down the group and decreases across a period.
On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9.
(a) Name the most electropositive element among them.
(b) Name the most electronegative element.
(c) Name the element with the smallest atomic size.
(d) Name the element, which is a metalloid.
(e) Name the element which shows maximum valency.
(a) Lithium (3)
(b) Fluorine (9)
(c) Fluorine (9)
(d) Boron (5)
(e) Carbon (6). Its valency is 4.
Q.20. An element X which is a yellow solid at room temperature shows catenation and allotropy. X forms two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and are the major air pollutants.
(a) Identify the element X.
(b) Write the electronic configuration of X.
(c) Write the balanced chemical equation for the thermal decomposition of ferrous sulphate crystals.
(d) What would be the nature (acidic/basic) of oxides formed?
(e) Locate the position of the element in the Modern Periodic Table.
(a) ‘X’ is sulphur.
(b) Electronic configuration of ‘X' is 2, 8, 6.
(d) SO2 and SO3 are acidic oxides.
(e) It belongs to Group 16 and 3rd period.
Q.21. An element X of group 15 exists as diatomic molecule and combines with hydrogen at 773 K in the presence of the catalyst to form a compound, ammonia which has a characteristic pungent smell.
(a) Identify the element X. How many valence electrons does it have?
(b) Draw the electron dot structure of the diatomic molecule of X. What type of bond is formed in it?
(c) Draw the electron dot structure for ammonia, and what type of bond is formed in it?
(a) ‘X’ is nitrogen. It has 5 valence electrons.
The bond formed is a covalent bond.
Q.22. Which group of elements could be placed in Mendeleev’s Periodic Table without disturbing the original order? Give reason.
Ans. Noble gases can be placed in a separate group without disturbing original order as the elements are arranged in increasing order of their atomic masses in Mendeleev’s Periodic Table.
Q.23. Give an account of the process adopted by Mendeleev for the classification of elements. How did he arrive at “Periodic Law”?