Lesson: Periodic Classification of Elements
Upto which element, the Law of Octaves was found to be applicable:
According to Mendeleev’s Periodic Law, the elements were arranged in the periodic table in the order of:
(a) Increasing atomic number
(b) Decreasing atomic number
(c) Increasing atomic masses
(d) Decreasing atomic masses
In Mendeleev’s Periodic Table, gaps were left for the elements to be discovered later.
Which of the following elements found a place in the periodic table later?
Which of the following statement(s) about the Modern Periodic Table is(are) incorrect:
(i) The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number.
(ii) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses.
(iii) Isotopes are placed in adjoining group(s) in the Periodic Table.
(iv) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number.
(a) (i) only
(b) (i), (ii) and (iii)
(c) (i), (ii) and (iv)
(d) (iv) only
Which of the following statements about the Modern Periodic Table are correct:
(a) It has 18 horizontal rows known as Periods
(b) It has 7 vertical columns known as Periods
(c) It has 18 vertical columns known as Groups
(d) It has 7 horizontal rows known as Groups
Which of the given elements A, B, C, D and E with atomic number 2, 3, 7, 10 and 30 respectively belong to the same period?
(a) A, B, C
(b) B, C, D
(c) A, D, E
(d) B, D, E
The elements A, B, C, D and E have atomic number 9, 11, 17, 12 and 13 respectively.
Which pair of elements belong to the same group?
(a) A and B
(b) B and D
(c) A and C
(d) D and E
Where would you locate the element with electronic configuration 2,8 in the Modern Periodic Table?
(a) Group 8
(b) Group 2
(c) Group 18
(d) Group 10
An element which is an essential constituent of all organic compounds belongs to:
(a) Group 1
(b) Group 14
(c) Group 15
(d) Group 16
Which of the following is the outermost shell for elements of period 2?
(a) K shell
(b) L shell
(c) M shell
(d) N shell
Which one of the following elements exhibit maximum number of valence electrons?
Which of the following gives the correct increasing order of the atomic radii of O, F and N?
(a) O, F, N
(b) N, F, O
(c) O, N, F
(d) F, O, N
Which among the following elements has the largest atomic radii?
Which of the following elements would lose an electron easily?
Which of the following elements does not lose an electron easily?
Which of the following are the characteristics of isotopes of an element?
(i) Isotopes of an element have same atomic masses
(ii) Isotopes of an element have same atomic number
(iii) Isotopes of an element show same physical properties
(iv) Isotopes of an element show same chemical properties
(a) (i), (iii) and (iv)
(b) (ii), (iii) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)
Arrange the following elements in the order of their decreasing metallic character:
Na, Si, Cl, Mg, Al
(a) Cl > Si > Al > Mg > Na
(b) Na > Mg > Al > Si > Cl
(c) Na > Al > Mg > Cl > Si
(d) Al > Na > Si > Ca > Mg
Arrange the following elements in the order of their increasing non-metallic character Li, O, C, Be, F
(a) F < O < C < Be < Li
(b) Li < Be < C < O < F
(c) F < O < C < Be < Li
(d) F < O < Be < C < Li
What type of oxide would Ekaaluminium form?
Three elements B, Si and Ge are:
(d) Metal, non-metal and metalloid respectively
Which of the following elements will form an acidic oxide?
(a) An element with atomic number 7
(b) An element with atomic number 3
(c) An element with atomic number 12
(d) An element with atomic number 19
The element with atomic number 14 is hard and forms acidic oxide and a covalent halide.
To which of the following categories does the element belong?
(d) Left-hand side element
Which one of the following depicts the correct representation of atomic radius(r) of an atom?
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
Which one of the following does not increase while moving down the group of the periodic table?
(a) Atomic radius
(b) Metallic character
(d) Number of shells in an element
On moving from left to right in a period in the periodic table, the size of the atom.
(c) Does not change appreciably
(d) First decreases and then increases
Which of the following set of elements is written in order of their increasing metallic character?
(a) Be Mg Ca
(b) Na Li K
(c) Mg Al Si
(d) C O N
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 arrangement of these elements is known as Döbereiner’s triad.
Example: Lithium, Sodium and Potassium
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?
(a) (i) F and Cl
(ii) Na and K.
(b) Newland’s law of octaves
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.
(a) No, because all these elements do not have similar properties although the
atomic mass of silicon is approximately average of the atomic masses of
sodium (Na) and chlorine (Cl).
(b) Yes, because they have similar properties and the mass of magnesium (Mg) is
roughly the average of the atomic mass of Be and Ca. Therefore, they form a
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.
This was done to ensure that elements with similar chemical properties were placed in the same group.
“Hydrogen occupies a unique position in Modern Periodic Table”. Justify the statement.
Hydrogen has one electron in its outermost orbit. Alkali metals too have the same number of electrons in its outermost orbit. Hydrogen resembles alkali metals as well as halogens. Though hydrogen is placed along with alkali metals in group 1, hydrogen is not included in the discussion of group 1 metals.
Thus, hydrogen occupies a unique position in the modern periodic table and is studied separately.
Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev.
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 valences.
If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride?
; Covalent bonding.
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
Radius of Y is lesser than that of X because Y is the ion formed when X loses 2 electrons.
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
(b) Cl < Br < I < At
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.
Here (a), (b) and (d) are metals.
Write the formula of the product formed when the element A (atomic number 19) combines with the element B (atomic number 17). Draw its electronic dot structure. What is the nature of the bond formed?
The formula of the product will be AB.
The electron dot structure will be as given below:
The elements A and B will form an ionic bond.
A = K (Potassium)
B = Cl (Chlorine)
Arrange the following elements in the increasing order of their metallic character.
Mg, Ca, K, Ge, Ga.
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 or K
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 under water.
(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) Sodium (Na) in Group 1 and Period 3 or Potassium (K) in Group 1 and Period 4
(b) Phosphorus (P) in Group 15 and Period 3
(c) Carbon (C) in Group 14 and Period 2
(d) Helium (He) in Group 18 and Period 1
(e) Aluminium (Al) in Group 13 and Period 3
An element is placed in 2nd Group and 3rd Period of the Periodic Table, burns in 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
(a) An element in 2nd group and 3rd period is magnesium (Mg).
(b) The electronic configuration of magnesium is 2, 8, 2.
(c) When magnesium burns in the presence of air, magnesium oxide is formed. The balanced reaction would be:
(d) When magnesium oxide dissolves in water, magnesium hydroxide is formed. The balanced reaction would be:
(e) The electron dot structure is:
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?
(d)Identify the nature of bonding in the compound formed
(e) Draw the electron dot structure of the divalent halide.
(a) The atomic number of X is 17. So, its electronic configuration would be 2, 8, 7. This element would therefore belong to Group 17 and 3rd period. The atomic number of Y is 20. So, its electronic configuration would be 2, 8, 8, 2. This element would belong to Group 2 and 4th period.
(b) The electronic configuration of X is 2, 8, 7. It will be easier for X to gain an electron and complete its octet during formation of bonds. Thus, X is a non-metal.
(c) The electronic configuration of Y is 2, 8, 8, 2. It will be easier for Y to lose 2 electrons and complete its octet during formation of bonds. Thus, Y is a metal.
(d) Oxide of Y will be basic in nature. Also, the oxide will have ionic bond.
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
The table below gives the elements with atomic number 10, 20, 7, 14, their electronic configuration, group, period and valency:
2, 8, 8, 2
2, 8, 4
Complete the following cross word puzzle given below:
(1) An element with atomic number 12.
(2) Metal used in making cans and member of Group 14.
(3) A lustrous non-metal which has 7 electrons in its outermost shell.
(4) Highly reactive and soft metal which imparts yellow colour when subjected to
flame and is kept in kerosene.
(5) The first element of second Period
(6) An element which is used in making fluorescent bulbs and is second member
of Group 18 in the Modern Periodic Table
(7) A radioactive element which is the last member of halogen family.
(8) Metal which is an important constituent of steel and forms rust when exposed
to moist air.
(9) The first metalloid in Modern Periodic Table whose fibres are used in making
(a) In this ladder 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) H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca
(b) Group 1 H, Li, Na, K
Group 2 Be, Mg, Ca
Group 13 B, Al
Group 14 C, Si
Group 15 N, P
Group 16 O, S
Group 17 F, Cl
Group 18 He, Ne, Ar
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.
(c) Classify these elements as metals, non-metals or metalloids
(d) How many valence electrons are present in each one of them?
(a) The elements discovered after Mendeleev’s prediction are germanium (Ge) and gallium (Ga).
(b) Germanium (Ge) belongs to group 14 and period 4 while gallium (Ga) belongs to group 13 and period 4.
(c) Germanium (Ge) is a metalloid and gallium (Ga) is a metal.
(d) Germanium (Ge) has 3 valance electrons and gallium (Ga) has 4.
i. Electropositive nature of the element(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 smallest atomic size
(d) Name the element which is a metalloid
(e) Name the element which shows maximum valency.
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
(d) What would be the nature (acidic/basic) of oxides formed?
(e) Locate the position of the element in the Modern Periodic Table.
(a) The element described here is sulphur (atomic no. 16).
(b) The electronic configuration of sulphur is 2, 8, 6.
(c) When heated, ferrous sulphate gives, ferric oxide, sulphur dioxide and sulphur trioxide. The balanced equation for the reaction is:
(d) The oxides of sulphur are acidic in nature.
(e) Sulphur belongs to the 3rd period and group 16 of the Modern Periodic Table.
An element X of group 15 exists as diatomic molecule and combines with hydrogen at 773 K in 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.
(c) What type of bond is formed in it?
(d) Draw the electron dot structure for ammonia and what type of bond is formed in it?
(a) The element described here is nitrogen. It has atomic number 7. Its electronic configuration is 2, 5. It has 5 valence electrons.
Which group of elements could be placed in Mendeleev’s Periodic Table without disturbing the original order? Give reason.
Noble gases could be placed in Mendeleev’s periodic table without disturbing the original order.
According to Mendeleev’s classification, the properties of elements are the periodic function of their atomic masses. Noble gases are inert and could be placed in a separate group without disturbing the original order.
Give an account of the process adopted by Mendeleev for the classification of elements. How did he arrive at “Periodic Law”?
In 1869, Mendeleev made a remarkable contribution to the classification of elements. When Mendeleev selected his work, 63 elements were known. He examined the relationship between the atomic masses of the elements and their physical and chemical properties. Among the chemical properties, the compounds of these elements with oxygen and hydrogen were studied (formation of oxides and hydrides). He then took 63 cards and on each he wrote down the properties of one element. He sorted out the elements with similar properties and paired the cards together. He observed that, elements with similar properties recur at regular intervals or periodically. He also observed that most of the elements get a place in the periodic table and was arranged in order of their increasing atomic masses.
On this basis, Mendeleev formulated a periodic law, which states that “the properties of elements are the periodic function of their atomic masses”.