Upto which element, the Law of Octaves was found to be applicable
Oxygen
Calcium
Cobalt
Potassium
According to Mendeleev’s Periodic Law, the elements were arranged in the periodic table in the order of
increasing atomic number
decreasing atomic number
increasing atomic masses
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
Germanium
Chlorine
Oxygen
Silicon
Which of the following statement(s) about the Modern Periodic Table 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
(i) only
(i), (ii) and (iii)
(i), (ii) and (iv)
(iv) only
Which of the following statements about the Modern Periodic Table is correct:
It has 18 horizontal rows known as Periods
It has 7 vertical columns known as Periods
It has 18 vertical columns known as Groups
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, B, C
B, C, D
A, D, E
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 and B
B and D
A and C
D and E
Where would you locate the element with electronic configuration 2,8 in the Modern Periodic Table?
Group 8
Group 2
Group 18
Group 10
An element which is an essential constituent of all organic compounds belongs to
group 1
group 14
group 15
group 16
Which of the following is the outermost shell for elements of period 2?
K shell
L shell
M shell
N shell
Which one of the following elements exhibit maximum number of valence electrons?
Na
Al
Si
P
Which of the following gives the correct increasing order of the atomic radii of O, F and N?
O, F, N
N, F, O
O, N, F
F, O, N
Which among the following elements has the largest atomic radii?
Na
Mg
K
Ca
Which of the following elements would lose an electron easily?
Mg
Na
K
Ca
Which of the following elements does not lose an electron easily?
Na
F
Mg
Al
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
(i), (iii) and (iv)
(ii), (iii) and (iv)
(ii) and (iii)
(ii) and (iv)
Arrange the following elements in the order of their decreasing metallic character: Na, Si, Cl, Mg, Al
Cl > Si > Al > Mg > Na
Na > Mg > Al > Si > Cl
Na > Al > Mg > Cl > Si
Al > Na > Si > Ca > Mg
Arrange the following elements in the order of their increasing non-metallic character: Li, O, C, Be, F
F < O < C < Be < Li
Li < Be < C < O < F
F < O < C < Be < Li
F < O < Be < C < Li
What type of oxide would Eka-aluminium form?
EO₃
E₃O₂
E₂O₃
EO
Three elements B, Si and Ge are
metals
non-metals
metalloids
metal, non-metal and metalloid respectively
Which of the following elements will form an acidic oxide?
An element with atomic number 7
An element with atomic number 3
An element with atomic number 12
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?
Metal
Metalloid
Non-metal
Left-hand side element
Which one of the following depict the correct representation of atomic radius (r) of an atom?
(i) and (ii)
(ii) and (iii)
(iii) and (iv)
(i) and (iv)
Which one of the following does not increase while moving down the group of the periodic table?
Atomic radius
Metallic character
Valence
Number of shells in an element
On moving from left to right in a period in the periodic table, the size of the atom
increases
decreases
does not change appreciably
first decreases and then increases
Which of the following set of elements is written in order of their increasing metallic character?
Be < Mg < Ca
Na < Li < K
Mg < Al < Si
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 is called a 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 Döbereiner's triad?
(a) Na, Si, Cl
(b) Be, Mg, Ca
Atomic masses: Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40. Explain by giving reason.
(a) No. These elements do not have similar properties so they cannot be classified as a Döbereiner triad, even though Si's atomic mass lies between Na and Cl.
(b) Yes. Be, Mg and Ca have similar properties and the atomic mass of Mg is approximately the average of Be and Ca, so they form a Döbereiner triad.
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.
Elements were arranged by chemical properties as well as atomic masses. Cobalt was placed before nickel because its chemical properties (and its position in the periodic pattern of properties) fitted that place better despite the small difference in atomic mass.
"Hydrogen occupies a unique position in Modern Periodic Table". Justify the statement.
Hydrogen resembles alkali metals (Group 1) in having one electron and can form H+ but it also resembles halogens in forming H− and covalent compounds. Thus it shows properties of both groups and occupies a unique position.
Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev.
Eka-silicon: GeCl4.
Eka-aluminium: GaCl3.
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.
Element A: Group 13 (valency 3).
Element B: Group 14 (valency 4).
Element C: Group 2 (valency 2).
If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride?
Formula: XCl4.
Nature of bonding: 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
Y is a cation of X (Y has lost two electrons) and therefore has a smaller radius than X because reduced electron–electron repulsion and greater effective nuclear attraction shrink the radius of Y compared to X.
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
Metals: (a) 2,8,2 → Magnesium (Mg).
(b) 2,8,1 → Sodium (Na).
(d) 2,1 → Lithium (Li).
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?
Product formula: KCl.
Electronic dot structure: K : → :Cl (transfer of one electron from K to Cl forming K⁺ and Cl⁻).
Nature of bond: Ionic bond.
Arrange the following elements in the increasing order of their metallic character: Mg, Ca, K, Ge, Ga.
Increasing metallic character: Ge < Ga < Mg < Ca < K.
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) Soft and reactive metal: Sodium (Na) or Potassium (K).
(b) Important constituent of limestone: Calcium (Ca).
(c) Metal liquid at room temperature: Mercury (Hg).
Increasing reactivity order: Hg < Ca < Na < 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) — Group 1, Period 3 (or Potassium (K) — Group 1, Period 4).
(b) Phosphorus (P) — Group 15, Period 3 (variable valency).
(c) Carbon (C) — Group 14, Period 2 (tetravalent, basis of organic chemistry).
(d) Helium (He) — Group 18, Period 1 (inert gas with atomic number 2).
(e) Aluminium (Al) — Group 13, Period 3 (forms thin oxide layer used in anodising).
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) Identification of the element: The element placed in Group 2 and Period 3 is magnesium (Mg).
(b) Electronic configuration: \( 1s^2 \ 2s^2 \ 2p^6 \ 3s^2 \). Using shell representation: K = 2, L = 8, M = 2.
(c) Balanced equation for burning in air:
\[ 2Mg(s) + O_2(g) \rightarrow 2MgO(s) \]
(d) Reaction of the oxide with water:
\[ MgO(s) + H_2O(l) \rightarrow Mg(OH)_2(aq) \]
(e) Electron dot structure:
Magnesium loses two electrons to form \( Mg^{2+} \), and oxygen gains two electrons to form \( O^{2-} \). The final dot structure represents ionic bonding: \( Mg^{2+} : O^{2-} \).
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) Position of elements:
Element X (Z = 17): Group 17, Period 3.
Element Y (Z = 20): Group 2, Period 4.
(b) Classification:
X is a non-metal (halogen). Y is a metal (alkaline earth metal).
(c) Nature of oxide and bonding:
Element Y forms a basic oxide because it is a Group 2 metal. The compound formed between X and Y is ionic because Y donates two electrons and X accepts one electron each.
(d) Electron dot structure:
\( Y^{2+} \Rightarrow [ X^{-} : X^{-} ] \). Each halogen atom gains one electron from Y, forming a divalent ionic halide \( YX_2 \).
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) Identification:
10 → Neon (Ne)
20 → Calcium (Ca)
7 → Nitrogen (N)
14 → Silicon (Si)
(b) Group numbers:
Ne → Group 18
Ca → Group 2
N → Group 15
Si → Group 14
(c) Period numbers:
Ne → Period 2
Ca → Period 4
N → Period 2
Si → Period 3
(d) Electronic configurations:
Ne: \( 1s^2 2s^2 2p^6 \)
Ca: \( 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 \)
N: \( 1s^2 2s^2 2p^3 \)
Si: \( 1s^2 2s^2 2p^6 3s^2 3p^2 \)
(e) Valency:
Ne → 0 (inert gas)
Ca → 2
N → 3
Si → 4
Complete the crossword puzzle (Figure 5.1) using the given clues.
Across:
(1) An element with atomic number 12
(3) Metal used in making cans and a member of Group 14
(4) A lustrous non-metal which has 7 electrons in its outermost shell
Down:
(2) Highly reactive and soft metal which imparts yellow colour when subjected to flame and is kept in kerosene
(5) The first element of the second Period
(6) An element used in making fluorescent bulbs and second member of Group 18
(7) A radioactive element which is the last member of halogen family
(8) Metal important in steel and forms rust in moist air
(9) The first metalloid in the Modern Periodic Table used in making bullet-proof vests
Completed crossword answers:
(1) Magnesium
(3) Tin
(4) Iodine
Down:
(2) Sodium
(5) Lithium
(6) Neon
(7) Astatine
(8) Iron
(9) Boron
In the ladder (Figure 5.2) symbols of elements are jumbled. Rearrange these symbols of elements:
(a) In the increasing order of their atomic number
(b) In the order of their groups
(a) Increasing order of atomic number:
H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca
(b) Order based on groups:
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 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) Modern equivalents:
Eka-silicon → Germanium (Ge)
Eka-aluminium → Gallium (Ga)
(b) Group and period:
Ge → Group 14, Period 4
Ga → Group 13, Period 4
(c) Classification:
Ge → Metalloid
Ga → Metal
(d) Valence electrons:
Ge → 4
Ga → 3
Based on the trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9:
(a) Name the most electropositive element
(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
Answers based on periodic trends:
(a) Lithium (most electropositive)
(b) Fluorine (most electronegative)
(c) Fluorine (smallest atomic size)
(d) Boron (metalloid)
(e) Carbon (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 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) Identification: The element X is sulphur (S).
(b) Electronic configuration: \( 1s^2 2s^2 2p^6 3s^2 3p^4 \). Shell notation: K = 2, L = 8, M = 6.
(c) Thermal decomposition of ferrous sulphate:
\[ 2FeSO_4(s) \xrightarrow{\text{Heat}} Fe_2O_3(s) + SO_2(g) + SO_3(g) \]
(d) Nature of the oxides: Both \( SO_2 \) and \( SO_3 \) are acidic oxides.
(e) Position in the Modern Periodic Table: Period 3, Group 16.
An element X of group 15 exists as a diatomic molecule and combines with hydrogen at 773 K in presence of a catalyst to form ammonia. Ammonia 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 state the type of bond formed in it
(a) Identification: X is nitrogen (N). It has 5 valence electrons.
(b) Electron dot structure of \( N_2 \): The two nitrogen atoms share three electron pairs forming a triple covalent bond.
(c) Electron dot structure of ammonia (NH3): Nitrogen forms three single covalent bonds with three hydrogen atoms. The structure shows three shared pairs and one lone pair on nitrogen.
Which group of elements could be placed in Mendeleev’s Periodic Table without disturbing the original order? Give reason.
The noble gases (Group 18) could be added to Mendeleev’s Periodic Table without disturbing the existing arrangement. This is because they are inert and chemically unreactive. Their placement as a separate group does not affect the order of other elements, which were arranged based on their valency and atomic mass.
Give an account of the process adopted by Mendeleev for the classification of elements. How did he arrive at the “Periodic Law”?
Mendeleev examined all known 63 elements and studied their properties, including the formation of oxides and hydrides. He grouped together the elements showing similar properties and arranged them in order of increasing atomic masses.
He observed a periodic recurrence of similar physical and chemical properties at regular intervals when arranged by atomic mass. This led him to propose the Periodic Law: “The properties of elements are a periodic function of their atomic masses.”