CBSE Class 10 Chemistry Periodic Classification of Elements Worksheet Set B

Question. By considering their position in the periodic table, which one of the following elements would you expect to have maximum metallic characteristic?
Ga, Ge, As, Se, Be
Answer: Metallic character of an element is defined as the easiness of its atom in losing electrons. According to the modern periodic table, the metallic character of an element decreases while moving from left to right across a period and increases down the group. Among the elements Ga, Ge, As, Se Be, Be and Ga are expected to be most metallic and out of Be and Ga, Ga is bigger in size and hence has a greater tendency to lose electrons than Be. Thus, Ga is more metallic than Be.

Question. The electronic configuration of two elements X and Y are 2, 8, 8, 3 respectively. Write atomic numbers of X and Y.*
Answer: Atomic number of X = 2, 8, 7 = 17
Atomic number of Y = 2, 8, 8, 3 = 21

Question. Answer the following questions:
(i) How would the tendency to lose electrons change as we go from left to right across a period of the periodic table?
(ii) How do the atomic radii of elements change as we go from left to right in a period of the periodic table?
Answer: (i) On moving from left to right in a period, the tendency of atoms to lose electrons decreases.
(ii) On moving from left to right in a period, the atomic size decreases.

Question. State one reason for placing Mg and Ca in the same group of the periodic table.
Answer: They have same number of valence electrons and show similar chemical properties.

Question. Elements have been arrangement in the following sequence on the basis of their increasing atomic masses.
F, Na, Mg, Al, Si, P, S, Cl, Ar, K
(i) Pick two sets of elements which have similar properties.
(ii) The given sequence represents which law of classification of elements?
Answer: (i) (a) F and Cl (b) Na and K.
(ii) Newland’s law of octaves.

Question. The atomic numbers of three elements A, B and C are 12, 18, and 20 respectively. State giving reason, which two elements will show similar properties.
Answer: A and C will show similar properties due to same number of valence electrons i.e., 2.

Question. Write any one difference between the electronic configuration of group-1 and group -2 elements.
Answer: Group 1 elements have 1 valence electron while group 2 elements have 2 valence electrons.

Question. The atomic numbers of three elements X, Y and Z are 3, 11 and 17 , respectively. State giving reason which two elements will show similar chemical properties.
Answer: The two elements X and Y will show same chemical properties because they have same number of valence electron in group.
They form positively charged ions by losing one electron.

Question. What were the criteria used by Mendeleev in creating his periodic table?
Answer: Mendeleev’s periodic table was based on atomic masses and similarity in formula of hydrides and oxides of elements.
According to him, the properties of elements are a periodic function of their atomic masses.

Question. Compare the radii of two species X and Y. Give reasons for your answer.
(i) X has 12 protons and 12 electrons, (ii) Y has 12 protons and 10 electrons.
Answer: Y has less electrons than X. This means that Y is cation of X. Therefore, radii of Y is less than X.

Short Answer Type Questions :

Question. Answer the following questions:
(i) How many groups and periods are there in the modern periodic table? How do the atomic size and metallic character of elements vary as we move:
(a) down a group and
(b) from left to right in a period
(ii) State the changes in valency and metallic character of elements as well as we move from left to right in a period.
Also state the changes, if any, in the valency and atomic size of elements as we move down a group.
Answer: (i) There are a total of 18 groups and 7 periods in a periodic table.
(a) As we move down the group the atomic size as well as metallic character of elements increases.
(b) Both metallic character and atomic size decreases as we move from left to right in a period.
(ii) Valency increases and the metallic character decreases as we move from left to right. Valency remains same and the size increases as we move down the group in periodic table.

Question. The position of three elements A, B and C in the Periodic Table are shown below: 
(i) State whether A is a metal or non-metal.
(ii) State whether C is more reactive or less reactive than A.
(iii) Will C be larger or smaller in size than B?
(iv) Which type of ion, cation or anion, will be formed by element A?
Answer: (i) A is a non-metal.
(ii) C is less reactive than A, as reactivity decreases down the group in halogens.
(iii) C will be smaller in size than B as moving across a period, the nuclear charge increases and therefore, electrons come closer to the nucleus.
(iv) A will form an anion as it accepts an electron to complete its octet.

Question. Which group of elements could be placed in Mendeleev’s periodic table without disturbing the original order? Give reason.
Answer: 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 and there is a periodic recurrence of elements with similar physical and chemical properties. Noble gas being inert, could be placed in a
separate group without disturbing the original order.

Question. How it can be proved that the basic structure of the Modern Periodic Table is based on the electronic configuration of atoms of different elements?
Answer: Modern periodic law states that the physical and chemical properties of an element are the periodic function of the atomic number of that element. Electronic configuration of the elements plays an important role in the placement of element in the modern periodic table. The valence shell electron on an element decides its position in a particular group or period for example, if the configuration of an element is 2, 1 it means that the element is lithium (Li = 2, 1) and it belongs to the 2nd period and 1st group of the modern periodic table.

Question. Answer the following questions:
(i) What property do all elements in the same column of the periodic table as boron have in common?
(ii) What property do all elements in the same column of the periodic table as fluorine have in common?
Answer: (i) All the elements in the same column as boron have the same number of valence electrons i.e., 3. Hence, they all have valency equal to 3.
(ii) All the elements in the same column as fluorine have the same number of valence electrons i.e., 7. Hence, they all have valency equal to 1.

Question. An element belongs to third period and group 16 of modern periodic table.
(i) Determine the number of valence electrons and valency of T.
(ii) Molecular formula of the compound when X reacts with hydrogen and write its electron dot structure.
(iii) Name the element X and state whether it is metallic or nonmetallic.
Answer: (i) Valency electron = 6
Valency = 2
(ii) H2S
(iii) Sulphur, Non-metal.

Question. An element X has both K and L shell completely filled with electrons. The element has atomic number 10.
(i) Identify the element.
(ii) To which group does it belong?
(iii) Write its electronic configuration.
Answer: (i) The element is Neon.
(ii) It belongs to group 18 of periodic table.
(iii) Electronic configuration: 2,8.

Question. The electronic configuration of an element is 2, 8, 4. State its:*
(i) Group and period in the Modern Periodic Table.
(ii) Name and write its one physical property.
Answer: (i) Si = 2, 8, 4
(a) It means that it belongs to 3rd period and 14th group.
(b) The name of element is silicon.
(ii) It is a metalloid. (i.e., element that has properties of both metals and non-metals).

Question. The atomic numbers of the three elements X, Y and Z are 2, 6 and 10 respectively. Which two elements belong to the same group ? Which two elements belong to the same period ? Give reasons for your choice.
Answer: X (2) and Z (2, 8). Both X and Z have zero valency hence they belong to same group: noble gases. Y and Z. Y: 2, 4 and Z: 2, 8 so, both of them belong to second period with two shells filled.

Question. An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide.
(i) Where in the periodic table are elements X and Y placed?
(ii) Classify X and Y as metal (s), non-metal (s) or metalloid (s).
(iii) What will be the nature of oxide of element Y ? Identify the nature of bonding in the compound formed.
(iv) Draw the electron dot structure of the divalent halide.
Answer: (i) X belongs to Group 17 and 3rd period Y belongs to Group 2 and 4th period.
(ii) X — Non-metal and Y — Metal.
(iii) Basic oxide; Ionic bonding. 

Question. An element ‘P’ belongs to group = 2 and period = 3, state whether it is a metal or nonmetal and nature of its oxides.
Answer : Group 2 = Metals
Nature of oxide = Basic oxide

Question. Fluorine, chlorine, bromine belong to same group. What is common between them?
Answer : All three elements i.e. fluorine, chlorine, bromine, have same number of valence electrons and same valency.

Question. The electronic configuration of an atom is 2, 8, 7. Give its atomic number, nature of oxide.
Answer : Electronic configuration = 2, 8, 7
∴ Atomic number = 17
Nature of oxide = Acidic oxide

Question. An element ‘A’ has atomic number 11, name the period and group number to which it belongs.
Answer : A’ — atomic number = 11
Electronic configuration = K L M
2, 8, 1
∴ Period number = Shell No. = 3
Group number = Valence electron = 1

Question. What are metalloids? Give 2 examples.
Answer : The elements which show some properties of metal and some properties of non-metal are called semi-metals or metalloids. Example — Boron, Silicon, Germanium, Arsenic.

Question. Atomic number of 4 elements is given below which element will belong to the group of Helium.
     W     X     Y        Z
     8     15     36     20
Answer : Element Y, with atomic number 36 will belong to the same group as He.
Both are inert gas.
atomic number of Y 36 = 2, 8, 18, 8
atomic number of helium 4 = 2, 2

Question. The following elements belong to same period arrange them in order.
    ​​​​​​​    ​​​​​​​    ​​​​​​​    ​​​​​​​    ​​​​​​​    ​​​​​​​    ​​​​​​​    ​​​​​​​X     Y     Z
Atomic Radius → 231 262 242
Answer :                    Y        Z         X
                                262     242     231
                                ⚪       ◯        〇
The atomic size decreases in a period.

Question. What is the valency of magnesium with atomic number 12 and nitrogen with atomic number 7?
Answer : Magnesium, atomic number = 12
Electronic configuration = 2, 8, 2
∴ Valency = 2
Nitrogen, atomic number = 7
Electronic configuration = 2, 5
∴ Valency = 3

Question. How many shells are present in all the elements that belong to period 3?
Answer : All elements in period 3 contain 3 shells in which the electrons are distributed (K, L, M).

Question. What happens to the electropositive character of elements as we move from left to right of the period in the Periodic Table?
Answer : On moving from left to right in a period, the electropositive character decreases as the tendency to lose electrons decreases.

Question. What are halogens? Where are they located in the Periodic Table?
Answer : Halogens are those elements which react with metals to form salts. They are present in 17th group of the Periodic Table.

Long Answer Type Questions :

Question. An element belongs to group 2 and element Q belongs to group 17 of long form of periodic table.
(i) How many valence electrons are there in P?
(ii) What is the valency of P?
(iii) How many valence electrons are there in Q?
(iv) What is the valency of Q?
(v) Write the chemical formula of P and Q.
Answer: (i) P has 2 valency electrons as valence electrons are equal to group number.
(ii) Valency of P is +2.
(iii) Q has 7 valence electrons.
(iv) Valency of Q is – 1. (valency = group number – 18 i.e., 17 -18)
(v) The formula of the compound is PQ2.

Question. Compare and contrast the arrangement of elements in Mendeleev’s periodic Table and the Modern Periodic Table.
Answer: 

Question. Mendeleev arranged 63 elements known at that time in the periodic table. According to Mendeleev “the properties of the elements are a periodic function of their atomic masses.” The table consists of eight vertical columns called ‘groups’ and horizontal rows called ‘periods’. Merits of Mendeleev’s Periodic Table: At some places the order of atomic weight was changed in order to justify the chemical and physical nature. Mendeleev left some gap for new elements which were not discovered at that time. One of the strengths of Mendeleev’s periodic table was that, when inert gases were discovered they could be placed in a new group without disturbing the existing order. Its main characteristics are that the elements are arranged in vertical rows called groups and horizontal rows called periods. 183
(i) What is the basis of arrangement of elements in Mendeleev’s periodic table?
(ii) Why were there some gaps in Mendeleev’s periodic table?
(iii) State whether the statement is true or false. Mendeleev’s periodic table consists of eight vertical columns called ‘groups’ and horizontal rows called ‘periods’.
(iv) X, Y and Z are the elements of a Dobereiner’s triad. If the atomic mass of X is 7. and that of Z is 39. What should be the atomic mass of Y?
Answer: (i) In Mendeleev’s periodic table, elements are arranged according to atomic masses.
(ii) There were some gaps in Mendeleev’s periodic table for unknown elements.
(iii) Mendeleev’s periodic table was divided into groups and columns. Therefore, the given statement is true.
(iv) According to Dobereiner’s triad, the atomic mass of middle element is the average of other two elements. Therefore, (7 + 39) = 46/2 Y = 23.

Reasoning Based Questions :

Question. The elements Li, Na and K each having one valence electron are in the period 2, 3 and 4 respectively of Modern Periodic Table.
(i) In which group of the periodic table should they be?
(ii) Which one of them is least reactive?
(iii) Which one of them has the largest atomic radius? Give reason to justify your answer.
Answer: (i) They belong to group 1 because they have one valence electrons.
(ii) Lithium is least reactive.
(iii) Potassium has largest size because atomic size increases down the group.

Question. Write the name given to the vertical columns and horizontal rows in the Modern Periodic Table. How does the metallic character of elements vary on moving down a vertical column? How does the size of atomic radius vary on moving left to right in a horizontal row? Give reason in support of your answer in the above two cases.
Answer: Vertical columns are called groups and horizontal rows are called periods. Metallic character increases down the group. As the size increases, the distance between electron and nucleus increases and attraction between nucleus and valence electrons decreases. Atomic size decreases on moving left to right in a period because electron is added in the same shell. So attraction between nucleus and valence shell increases due to which the outermost shell is pulled in closer to the nucleus.
Nuclear charge is also increasing. Thus, effective nuclear charge increases and atomic size decreases.

Question. Nitrogen (Atomic number 7) and phosphorous (atomic number 15) belong to group 15 of the periodic table. Write the electronic configuration of these two electrons. Which of these will be more electronegative and why?
Answer: Nitrogen = 2, 5
Phosphorous = 2, 8, 5
N is more electronegative than P as from top to bottom down a group, electronegativity decreases. This is because number of shell increases down a group, and thus there is an increased distance between the valence electrons and nucleus, or a greater atomic radius.

Question. Why do you think the noble gases are placed in a separate group?
Answer: Noble gases are placed in a separate group because these are inert elements. They have properties which are different from all other elements.

Question. What is meant by atomic radius? Explain why it the decreases across a period?
Answer: The distance from centre of nucleus to outermost shell of an atom is atomic radius. Atomic radius decrease across a period because electron is added in the same shell. So attraction between nucleus and valence shell increases due to which outermost shell is pulled in closer to the nucleus. Nuclear charge is also increasing. Thus, effective nuclear charge
increases and atomic size decreases.

Question. Na, Mg and Al are the element of the same period of modern periodic table having one, two and three valence electrons respectively, which of these elements (i) has the largest atomic radius, (ii) is least reactive? Justify your answer starting reason for each case.
Answer: (i) Atomic radius decreases along the period with increase in atomic number. Therefore, the element with largest atomic radius is Na.
Na > Mg > Al
(ii) All these elements are metals. Reactivity of metals decreases with decrease in atomic radius along the period. Hence, Na is most reactive among the three. So, the order of reactivity is Na > Mg > Al.

Question. In the modern periodic table a zig-zag line separates metals from non-metals. What are these elements called and why?
Answer: A zig-zag line of elements that separates metal from nonmetals are known as metalloids because they have some properties of metals and some properties of non-metals.

Question. Why are elements chlorine, bromine and iodine called halogens?
Answer: Element chlorine, bromine and iodine are called halogens because these elements reacts readily with alkali metal and alkaline earth metals to form halide salts. (halo - salt, gene -producer.).

Question. How does the metallic character of elements change along a period of the periodic table from the left to the right and why?
Answer: The metallic character goes on decreasing along a period from left to right because atomic size goes on decreasing therefore, tendency to lose electrons decreases.

Question. How does the tendency of the elements to lose electrons change in the Modern Periodic Table in (i) a group , (ii) a period and why?
Answer: (i) Increase down a group.
Reason: At each succeeding element down a group the number of shells from the nucleus increases, and the effective nuclear force of attraction decreases on the last shell, so it becomes easy for the atom to lose electrons.
(ii) Decreases in a period from left to right.
Reason: As the effective nuclear charge on the valence shell electron increases, the attraction between the valence electron and nucleus increases, so it becomes difficult to lose electrons.

Question. Explain why:
(i) The elements of the same group have similar chemical properties.
(ii) The elements of the same period have different properties.
Answer: (i) The elements of the same group have similar chemical properties because of the presence of same number of valence electrons.
(ii) The elements of the same period have different properties because number of valence electrons are different.

Case Based Questions :

Read the following and answer the following questions from Metallic character: The ability of an atom to donate electrons and form positive ion (cation) is known as electropositivity or metallic character. Down the group, metallic character increases due to increase in atomic size and across the period, from left to right electro-positivity decreases due to decrease in atomic size. Non-metallic character: The ability of an atom to accept electrons to form a negative ion (anion) is called non-metallic character or electronegativity. The elements having high electronegativity have a higher tendency to gain electrons and form anion. Down the group, electronegativity decreases due to increase in atomic size and across the period, from left to right electronegativity increases due to decrease in atomic size.

Question. Which of the following correctly represents the decreasing order of metallic character of Alkali metals plotted in the graph?
(a) Cs > Rb > Li > Na > K
(b) K > Rb > Li > Na > Cs
(c) Cs > Rb > K > Na > Li
(d) Cs > K > Rb > Na > Li

Answer: C

Question. Hydrogen is placed along with Alkali metals in the modern periodic table though it shows non-metallic character:
(a) as Hydrogen has one electron and readily loses electron to form negative ion
(b) as Hydrogen can easily lose one electron like alkali metals to form positive ion
(c) as Hydrogen can gain one electron easily like halogens to form negative ion
(d) as Hydrogen shows the properties of non-metals

Answer: B

Question. Which of the following has highest electro-negativity? 
(a) F
(b) Cl
(c) Br
(d) I

Answer: A

Question. Identify the reason for the gradual change in electronegativity in halogens down the group. 
(a) Electronegativity increases down the group due to decrease in atomic size
(b) Electronegativity decreases down the group due to decrease in tendency to lose electrons
(c) Electronegativity decreases down the group due to increase in atomic radius/tendency to gain electron decreases
(d) Electronegativity increases down the group due to increase in forces of attractions between nucleus and valence electrons

Answer: C

Question. Which of the following reason correctly justifies that, “Fluorine (72pm) has smaller atomic radius than Lithium (152pm)”? 
(a) F and Li are in the same group. Atomic size increases down the group.
(b) F and Li are in the same period. Atomic size increases across the period due to increase in number of shells.
(c) F and Li are in the same group. Atomic size decreases down the group.
(d) F and Li are in the same period and across the period atomic size/radius decreases from left to right.

Answer: D

Read the following passage carefully and answer the following questions from Atomic radius is defined as the distance between the center of the nucleus and the outermost shell of electrons. As the effective nuclear charge increases as we move left to right along a period, hence the atomic radii decreases. There is a decrease in atomic size from Li to F in the second period and from Na to Cl in the third period. In any period the noble size has the largest radius. 

Question. Which among the following has the maximum atomic radius? 
(a) Si
(b) P
(c) Mg
(d) Al

Answer: C

Question. The element which has the smallest size in group 13 is: 
(a) Aluminum
(b) Gallium
(c) Boron
(d) Thallium

Answer: C

Question. The reason due to which atomic radius decreases as we move across a period is: 
(a) atomic number decreases
(b) electrons are removed from the atom
(c) atomic mass increases
(d) effective nuclear charge increases

Answer: D

Question. The element having the smallest size in the third period of the periodic table is: 
(a) Argon
(b) Chlorine
(c) Silicon
(d) Sodium

Answer: B

Question. The correct order of increasing atomic radii for the element set [O, C, F, Cl, Br] is: 
(a) F, O, C, Cl, Br
(b) F, C, O, Cl, Br
(c) F, Cl, Br, O, C
(d) C, O, F, Cl, Br

Answer: A