Periodic Classification of Elements f

Lesson: Periodic Classification of Elements

Question: 1

Which of the following statements is not a correct statement about the trends when going from left to right across the periods of the Periodic Table?

(a) The elements become less metallic in nature.

(b) The number of valence electrons increases.

(c) The atoms lose their electrons more easily.

(d) The oxides become more acidic.

Solution:

(c)

Question:2

Element X forms a chloride with the formula XCl2$$, which is a solid with a high

melting point. X would most likely be in the same group of the Periodic Table as

(a) Na

(b) Mg

(c) AI

(d) Si

Solution:

(b)

Question:3

Which element has:

(a) two shells, both of which are completely filled with electrons?

(b) the electronic configuration 2, 8, 2?

(c) a total of three shells, with four electrons in its valence shell?

(d) a total of two shells, with three electrons in its valence shell?

(e) twice as many electrons in its second shell as in its first shell?

Solution:

(a) Neon

(b) Magnesium

(c) Silicon

(d) Boron

(e) Carbon

Question:4

(a) What property do all elements in the same column of the Periodic Table as boron have in common?

(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?

Solution:

(a) Valency equal to 3.

(b) Valency equal to 1.

Question:5

An atom has electronic configuration 2, 8, 7.

(a) What is the atomic number of this element?

(b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.)

N (7), F (9), P (15), Ar (18)

Solution:

(a) 17.

(b) Fluorine (F) with the configuration as 2, 7

Question:6

The position of three elements A, B and C in the Periodic Table are shown below

Group 16	Group 17
-	-
-	A
-	-
B	C

(a) State whether A is a metal or non-metal.

(b) State whether C is more reactive or less reactive than A.

(c) Will C be larger or smaller in size than B?

(d) Which type of ion, cation or anion, will be formed by element A?

Solution:

(a)   A is a non-metal.

(b)   C is less reactive than A, as reactivity decreases down the group in halogens.

(c)   C will be smaller in size than B as moving across a period, the nuclear charge increases. Therefore, electrons come closer to the nucleus.

(d)   A will form an anion as it accepts an electron to complete its octet.

Question:7

Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to

group 15 of the Periodic Table. Write the electronic configuration of these two

elements. Which of these will be more electronegative? Why?

Solution:

Nitrogen (7): 2, 5

Phosphorus (15): 2, 8, 5

Since, electronegativity decreases with moving from top to bottom in a group, nitrogen will be more electronegative.

Question:8

How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?

Solution:

In the Modern Periodic Table, atoms with similar electronic configurations are placed in the same column. In a group, the number of valence electrons remains the same. Elements across a period show an increase in the number of valence electrons.

Question:9

In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium?

Solution:

Both calcium and the elements with atomic number 12 and 38 have same number of valence electrons, i.e. 2. Hence both these elements have the same properties.

Question: 10

Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table

and the Modern Periodic Table.

Solution:

Mendeleev's Periodic Table	Modern Periodic Table
Elements are arranged in the increasing order of their atomic masses.	Elements are arranged in the increasing order of their atomic numbers.
There are 8 Groups.	There are 18 Groups.
Groups are subdivided into sub-groups.	Groups are not subdivided into sub-groups.
Groups for noble gases were not present.	A separate group is meant for noble gases.
Position of isotopes could not be explained by Mendeleev’s periodic table.	Position of isotopes is well explained.

 Lesson: Periodic Classification of Elements

Question: 1

Upto which element, the Law of Octaves was found to be applicable:

(a) Oxygen

(b) Calcium

(c) Cobalt

(d) Potassium

Solution:

(b)

Question:2

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 numbery

(c) Increasing atomic masses

(d) Decreasing atomic masses

Solution:

(c)

Question:3

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?

(a) Germanium

(b) Chlorine

(c) Oxygen

(d) Silicon

Solution:

(a)

Question: 4

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

Solution:

(b)

Question: 5

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

Solution:

(c)

Question:6

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

Solution:

(b) 

Question:7

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

Solution:

(c)

Question: 8

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

Solution:

(c)

Question: 9

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

Solution:

(b)

Question; 10

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

Solution:

(b)

Question: 11

Which one of the following elements exhibit maximum number of valence electrons?

(a) Na

(b) Al

(c) Si

(d) P

Solution:

(d)

Question: 12

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

Solution:

(d)

Question: 13

Which among the following elements has the largest atomic radii?

(a) Na

(b) Mg

(c) K

(d) Ca

Solution:

(c)

Question 14

Which of the following elements would lose an electron easily?

(a) Mg

(b) Na

(c) K

(d) Ca

Solution:

(c)

Question: 15

Which of the following elements does not lose an electron easily?

(a) Na

(b) F

(c) Mg

(d) Al

Solution:

(b) 

Question: 16

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)

Solution:

(d) 

Question: 17

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   

Solution:

(b) 

Question: 18

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

Solution:

(b) 

Question: 19

What type of oxide would Eka–$$aluminium form?

(a) EO3$$

(b) E3O2$$

(c) E2O3$$

(d) EO$$

Solution:

(c)

Question: 20

Three elements B, Si and Ge are:

(a) Metals

(b) Non-metals

(c) Metalloids

(d) Metal, non-metal and metalloid respectively

Solution:

(c)

Question: 21

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

Solution:

(a)

Question: 22

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?

(a) Metal

(b) Metalloid

(c) Non-metal

(d) Left-hand side element

Solution:

(b)

Question: 23

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)

Solution:

(b)

Question: 24

Which one of the following does not increase while moving down the group of the periodic table?

(a) Atomic radius

(b) Metallic character

(c) Valence

(d) Number of shells in an element

Solution:

(c)

Question 25

On moving from left to right in a period in the periodic table, the size of the atom.

(a) Increases

(b) Decreases

(c) Does not change appreciably

(d) First decreases and then increases

Solution:

(b)

Question: 26

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

Solution:

(a)

Question: 27

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.

Solution:

The arrangement of these elements is known as Döbereiner’s triad.

Example: Lithium, Sodium and Potassium

Question: 28

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?

Solution:

(a)        (i) F and Cl

            (ii) Na and K.

(b) Newland’s law of octaves

Question: 29

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.

Solution:

(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

Dobereiner’s triad.

Question: 30

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.

Solution:

This was done to ensure that elements with similar chemical properties were placed in the same group.

Question: 31

“Hydrogen occupies a unique position in Modern Periodic Table”. Justify the statement.

Solution:

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.

Question: 32

Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev.

Solution:

GeCl4, GaCl3$$

Question: 33

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.

Solution:

Element	Group No.	Valence
A	Group-13	3
B	Group-14	4
C	Group-2	2

Question: 34

If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride?

Solution:

XCl4$$; Covalent bonding.

Question: 35

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

Solution:

Radius of Y is lesser than that of X because Y is the ion formed when X loses 2 electrons.

Question: 36

Arrange the following elements in increasing order of their atomic radii.

(a) Li, Be, F, N

(b) Cl, At, Br, I.

Solution:

(a)  F < N < Be < Li

(b) Cl < Br < I < At

Question: 37

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.

Solution:

Here (a), (b) and (d) are metals.

(a) Magnesium

 (b) Sodium

(d) Lithium.

Question: 38

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?

Solution:

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)

Question: 39

Arrange the following elements in the increasing order of their metallic character.

Mg, Ca, K, Ge, Ga.

Solution:

Ge <  Ga < Mg < Ca < K$$

Question: 40

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

Solution:

(a) Na or K

(b) Ca

(c) Hg

Hg < Ca < Na < K$$ 

Question: 41

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”.

Solution:

(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

Question: 42

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

Solution:

(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:

2Mg(s)+O2(g)→2MgO(s)$$

(d)   When magnesium oxide dissolves in water, magnesium hydroxide is formed. The balanced reaction would be:

MgO(s)+H2O(l)→Mg(OH)2(aq)$$

(e)   The electron dot structure is:

Question: 43

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.

Solution:

(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 3^rd 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 4^th 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.

Question: 44

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

Solution:

The table below gives the elements with atomic number 10, 20, 7, 14, their electronic configuration, group, period and valency:

Atomic number	Element	Electronic configuration	Group	Period	Valency
10	Neon (Ne)	2, 8	18	2	0
20	Calcium (Ca)	2, 8, 8, 2	2	4	2
7	Nitrogen (7)	2, 5	15	2	3
14	Silicon (Si)	2, 8, 4	14	3	4

Question: 45

Complete the following cross word puzzle given below:

Across:

(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.

Down:

(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

bullet-proof vests.

Solution:

Question: 46

(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.

Solution:

(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

Question: 47

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?

Solution:

(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.

Question: 48

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.

Solution:

(a) Lithium

(b) Fluorine

(c) Fluorine

(d) Boron

(e) Carbon

Question: 49

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.

Solution:

(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:

2 FeSO4(s)−→−HeatFe2O(s)+SO2(g)+SO3(g)$$

(d)   The oxides of sulphur are acidic in nature.

(e)   Sulphur belongs to the 3^rd period and group 16 of the Modern Periodic Table.

Question: 50

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?

Solution:

(a)     The element described here is nitrogen. It has atomic number 7. Its electronic configuration is 2, 5. It has 5 valence electrons.

Question: 51

Which group of elements could be placed in Mendeleev’s Periodic Table without disturbing the original order? Give reason.

Solution:

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.

Question: 52

Give an account of the process adopted by Mendeleev for the classification of elements. How did he arrive at “Periodic Law”?

Solution:

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”.

Lesson: Periodic Classification of Elements

Question:1

Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves?

Compare and find out?

Solution:

Yes, Döbereiner's triads also existed in the columns of Newlands' Octaves.

The second column of the classification has Li, K, and Na which constitutes Döbereiner’s triads.

Question:2

What were the limitations of Döbereiner’s classification?

Solution:

Dobereiner’s triads had a major limitation that all known elements could not be classified into groups of triads having similar properties.

Question:3

What were the limitations of Newlands’ Law of Octaves?

Solution:

Limitations of Newlands' law of octaves are:

·         It was applicable up to calcium only. The properties of the elements listed

after calcium did not obey Newlands’ law of octaves.

·         To fit elements in his table, Newland had put two elements together in 

one slot that too having different properties.

·         Newland assumed the existence of only 56 natural elements. Several new elements that were discovered later could not be fit into the law of octaves.

Question:4

Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements:

K, C, AI, Si, Ba.

Solution:

·         K is in group 1. Therefore, the oxide will be K2O$$.

·         C is in group 4. Therefore, the oxide will be CO2$$.

·         Al is in group 3. Therefore, the oxide will be Al2O3$$.

·         Si is in group 4. Therefore, the oxide will be SiO2$$.

·         Ba is in group 2. Therefore, the oxide will be BaO$$.

Question:5

Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (Any two)

Solution:

Scandium and Germanium.

Question: 6

What were the criteria used by Mendeleev in creating his Periodic Table?

Solution:

Mendeleev used atomic mass of the elements as the unique criteria for creating his Periodic Table.

Mendeleev’s Periodic Table contains vertical columns called ‘groups’ and horizontal rows called ‘periods’. He proposed that the chemical properties of elements are the periodic function of their atomic masses.

Question: 7

Why do you think the noble gases are placed in a separate group?

Solution:

The noble gases are placed in a separate group in the Periodic Table as the valence shell of each of these gases is completely filled with electrons. All noble gases show similar chemical properties.

Question: 8

How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?

Solution:

The modern periodic table is an improvement over Mendeleev’s periodic table. In case of the modern periodic table, the elements are arranged in the increasing order of their atomic numbers.

The isotopes of an element have the same atomic number with different atomic masses. They have similar chemical properties and cannot be placed separately. Using the atomic number as the basis of classification helps explaining the position of isotopes in the periodic table.

The modern periodic table also clarifies the position of hydrogen as it is kept in the group with the elements having the same number of valence electrons.

Question: 9

Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?

Solution:

Calcium (Ca) and strontium (Sr) are expected to show chemical reactions similar to magnesium (Mg). This is because the number of valence electrons in all these three elements is 2.

Question: 10

Name:

(a) Three elements that have a single electron in their outermost shells.

(b) Two elements that have two electrons in their outermost shells.

(c) Three elements with filled outermost shells.

Solution:

(a) Lithium (Li), sodium (Na), and potassium (K)

(b) Magnesium (Mg) and calcium (Ca)

(c) Neon (Ne), argon (Ar), and xenon (Xe)

Question: 11

a)      Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?

b)      Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Solution:

a)      Yes, the atoms of all the three elements lithium, sodium, and potassium have one electron in their outermost shells.

b)      Both helium (He) and neon (Ne) have filled outermost shells. Helium has 

2 electrons in its K shell, while neon has 8 in its L shell.

Question: 12

In the Modern Periodic Table, which are the metals among the first ten elements?

Solution:

Lithium (Li) and beryllium (Be)

Question: 13

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$$ 

Solution:

The metallic character of an element decreases as one moves from left to right in a period. Since Be lies to the extreme left-hand side of the periodic table, it will have maximum metallic characteristic among the given elements.

Questions

Q1	Which element has the smallest atom with highest electronegativity?

Q2	How does the increase in atomic number affect the density of alkali metals?

Q3	State two merits of the Modern Periodic Table?

Q4	What is the common feature of the electronic configurations of the elements in Group 17?

Q5	What is meant by the electronegativity of an element?

Q6	Why do lanthanides and actinides have similar properties?

Q7	State two limitations of the law of octaves.

Q8	Define periodicity.

Q9	Why is it that the electron affinity of a noble gas is zero?

Q10	How will the tendency to gain electrons change as we go from left to right across a period?  Why?

Q11	Which period in the Modern Periodic Table is known as an incomplete period?

Q12	Why is a cation always smaller than the parent atom from which it is formed?

Q13	Why is atomic number more vital than any other quality to determine the characteristics of an element?

Q14	What are lanthanides and actinides?

Q15	Give 3 examples of each of the following: Metalloids, alkali metals, halogens, alkaline earth metals, noble gases or inert elements.

Q16	Two unknown elements A which has atomic number 9 and B which has atomic number 17 belong to group 17 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?

Q17	What are the defects of Mendeleev’s Periodic Table?

Q18	What are the factors that influence the atomic radius?

Q19	Compare the Mendeleev’s Periodic Table with the Modern Periodic Table.

Q20

An unknown element has 5 shells and 3 valence electrons. Which group and period does the element belong? Questions Q1 Which element has the smallest atom with highest electronegativity? A1 Fluorine is an element which has the smallest atom with highest electronegativity. Q2 How does the increase in atomic number affect the density of alkali metals? A2 With the increase in the atomic number, the density of alkali metals decreases. Q3 State two merits of the Modern Periodic Table? A3 It is based on the atomic numbers of the element. It helps to understand why elements in the same group show similar properties. Q4 What is the common feature of the electronic configurations of the elements in Group 17? A4 The common feature of the electronic configurations of the elements in Group 17 is that all the elements in the group have 7 valence electrons. Q5 What is meant by the electronegativity of an element? A5 The relative tendency of an element’s atom to attract a bonded pair of electrons in a molecule is called electronegativity. So, an element’s electron affinity is measured by its electronegativity. Q6 Why do lanthanides and actinides have similar properties? A6 Lanthanides and actinides have similar properties because they belong to the same Group 3. Q7 State two limitations of the law of octaves.   A7 Two limitations of the law of octaves: · The law of octaves was applicable up to calcium only. · It was on the assumption that only 56 elements existed in nature. Q8 Define periodicity. A8 The recurrence of properties at regular intervals or in which there is gradual variation of increase or decrease at regular intervals, are called ‘periodic properties’. This phenomenon is known as the periodicity of elements. Q9 Why is it that the electron affinity of a noble gas is zero? A9 Electron affinity is defined as the energy released by adding an electron to a gaseous atom or the energy required to remove an electron from a gaseous anion. A noble gas has fully filled orbitals and hence it has no scope of adding an extra electron and hence its electron affinity is practically zero. Q10 How will the tendency to gain electrons change as we go from left to right across a period?  Why? A10 On moving from left to right across a period, metallic character decreases and non-metallic character increases. Since metals tend to lose electrons and non-metals tend to gain electrons, the tendency to gain electrons increases as we move from left to right across a period. Q11 Which period in the Modern Periodic Table is known as an incomplete period? A11 In the Modern Periodic Table, the seventh period is known as an incomplete period because there are blank spaces in this period which are assumed to be filled by the elements discovered in future. Q12 Why is a cation always smaller than the parent atom from which it is formed? A12 A cation is formed by the loss of electrons from the outermost shell of the parent atom. Protons being more than electrons in a cation, electrons are strongly attracted by the nucleus and are pulled inward. Hence they cause the ionic radius to decrease. Q13 Why is atomic number more vital than any other quality to determine the characteristics of an element? A13 Atomic number is more vital than any other quality as electronic configuration is written for atomic number, which gives us a clear view about the number of valence electrons. It is in fact the number of valence electrons which decides the chemical properties of an element. Q14 What are lanthanides and actinides? A14 The inner transition elements are two series of elements known as the lanthanides and the actinides which are shown, below all the other elements in the standard view of the Periodic Table. They really belong to the periods 6 and 7. The lanthanide series consists of the 14 elements; cerium through lutetium (atomic numbers 58-71), which immediately follow lanthanum. Likewise, the actinide series consists of the 14 elements; thorium through lawrencium (atomic numbers 90-103), which immediately follow actinium. Q15 Give 3 examples of each of the following: Metalloids, alkali metals, halogens, alkaline earth metals, noble gases or inert elements. A15 Metalloids – Boron, germanium, silicon Alkali metals – Lithium, potassium, sodium Halogens – Bromine, chlorine, fluorine          Alkaline Earth metals – Barium, calcium, magnesium Noble gases or inert elements – Helium, krypton, neon Q16 Two unknown elements A which has atomic number 9 and B which has atomic number 17 belong to group 17 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why? A16 Element A Atomic number: 9 Electronic configuration: 2, 7 Element B Atomic number: 17 Electronic configuration: 2, 8, 7 Since, electronegativity decreases as we go down a group, element A will be more electronegative than element B. Q17 What are the defects of Mendeleev’s Periodic Table? A17 Mendeleev’s Periodic Table is not without flaws. 1) In spite of its properties having similarity with those of halogens, hydrogen is to be found in Group 1 and so its position is controversial. 2) According to Mendeleev’s Table, isotopes of an element should fill a different position but all isotopes have been located in the same block. 3) Elements with higher atomic weights were found to be placed prior to elements having lower atomic weights. For example, cobalt (Co) with atomic weight 58.94 is placed before nickel (Ni) with atomic weight 58.68. 4) Mendeleev’s Periodic Table fails to reflect the electronic build of elements. As the electronic structure is a very important property of an element, any classification of element must reveal it. Q18 What are the factors that influence the atomic radius? A18 There are two factors that influence the atomic radius. 1) Number of shells: With the addition of the number of shells, the distance between the outermost shell and the nucleus increases, hence the atomic radius too increases. 2) Nuclear charge: With the strengthening of nuclear charge, the force of attraction between the nucleus and electrons in the outermost shell increases thereby attracting the valence electronic shell nearer to the nucleus. Hence the atomic radius decreases. Q19 Compare the Mendeleev’s Periodic Table with the Modern Periodic Table. A19 Mendeleev’s Periodic Table Modern Periodic Table 1.   There are no distinct positions for isotopes of an element as their atomic masses are distinct. 1.      Distinct positions for isotopes are not necessary as they have same atomic numbers. 2.   Elements are arranged in the increasing order of their atomic masses. 2.      Elements are arranged in the increasing order of their atomic numbers. 3.   Some elements of higher atomic masses have been placed before elements of lower atomic masses. 3.      No such problems arise in this table. All elements are properly organized. 4.   Electronic configuration of an element cannot be calculated from its position. 4.      Electronic configuration of an element can be easily calculated from its position. 5.   Some unrelated elements are grouped together while some related elements are not grouped together. 5.      All related elements are grouped together. Q20 An unknown element has 5 shells and 3 valence electrons. Which group and period does the element belong? A20 The period, to which the element belongs depends upon the number of shells that the atom of the element has. Since it has five shells, the period number will be five. Depending upon the valence electrons, the group number is allotted. If there are 1 or 2 valence electrons, then the group number will be 1 and 2 respectively. But when there are 3 or more than 3 valence electrons, then the group number is obtained by adding 10 to the number of valence electrons. Therefore in this case, the group number will be 13.