Periodic Classification of Elements : Practice Questions



1 Mark Questions

 

1.  Write two reasons responsible for late discovery of noble gases.


2.  Write the valency and usual number of valence electrons of group 18 of the Periodic Table.


3.  Name the most metallic and most non- metallic elements in the Periodic Table.


4.  Mention the type of compounds formed between group 1 and group 17 elements.


5.  How many horizontal rows are there i the Modern Periodic Table and what are they called


6.  Modern Periodic Table, name the metals among the first ten elements.


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


8.  Give one example each of :

(i) Halogen

(ii) Alkali metals


9.  What is meant by periodicity in properties of elements with reference to Periodic Table ?


10.  Size of sodium atom is bigger than that of hydrogen atom. Why ?


11.  What is the similarity in the valency of all the elements of group 1 in the Modern Periodic Table ?


12. Write the electronic configuration of the element which belongs to second period and third group of the Periodic Table.


13.  Out of two elements potassium and sodium, which one can lose electron easily ? Give reason for your answer.


14.  How many shells are present in the elements of the second period ?


15.  Atomic radius of hydrogen is 37 pm. Express it in meters.


16.  An element 'X' forms a chloride with formula XCl3. The element 'X' would most likely be in the same group of the Periodic Table is Na, Mg, Al or Ca ?


17.  An element 'X' is in second period and group 16 of the Periodic Table. Is it metal or non - metal ? Give reason for your answer.


18.  Mention the common name give to the following elements :

Boron, Silicon, Germanium, Arsenic, Antimony.

State their one property that justifies their name.


19.  State the place of metalloids in the Periodic Table.


20.  Name the element which has twice as many electrons in its second shell as in its first shell. Write its electronic configuration also.


21.  Why are isotopes of an element having different atomic masses placed at the same position in the Periodic Table ?


22.  Elements A, B, C and D have atomic numbers 1, 8, 11 and 19 respectively. Choose the odd element and give reason for your answer.


23.  Account for the following :

Elements of group 17 are monovalent.


24.  Why do all the elements of the same period have different properties ?


25.  Account for the following :

Elements of group 18 are called zerovalent.

 

Solutions

 

1.  - Noble gases are very inert.

- They are present in extremely low concentrations in our atmosphere.


2.  - Valency – 0

- No. of valence electrons – 8


3.  - Most metallic element – Francium (Fr)

- Most non - metallic element – Helium (He)


4.  Ionic compounds.


5.  There are 7 horizontal rows in the Modern Periodic Table. These are called periods.


6.  Lithium (Li) and beryllium (Be).


7.  - XCl4

- Ionic bonds.


8.  (i) Chlorine (Cl)

(ii) Sodium (Na)


9.  The repetition of the properties of elements after regular intervals, when the elements are arranged in the order of their increasing atomic numbers, is called periodicity.


10.  Atomic size increases down the group as new shell are added.


11.  Valency is same i.e., 1.


12.  K   L

.      2    3


13.  Potassium, because the tendency to lose electron goes on increasing as we down the group.


14.  Two shells (K and L).


15.  1 pm = 10–12 m

Therefore, Atomic radius = 37 × 10–12 m


16.  Al.


17.  Non - metal because its atomic number is 16. So, electronic configuration will be 2, 8, 6 i.e., it can gain two electrons.


18.  All are metalloids. They have both the properties of metals as well as non - metals.


19.  Metalloids have been placed in the middle of the Periodic Table.


20.  - Carbon

- Electronic configuration : K  L

.                                               2  4


21.  All isotopes of an element have same number of protons and they have same atomic number. So, they can be put in one place.


22.  Odd element : B having atomic number 8.

Reason : B has six electrons in valence shell but A, C and D have one electron in their valence shells.


23.  Group 17 elements e.g., F, Cl, Br and I have seven valences electrons. By gaining one electron, they achieve inert gas configuration. Hence, they are called monovalent.


24.  All the elements of the same period have different properties because they have different number of valence electrons.


25.  Elements of group 18 have completely filled outermost shells and have no tendency to gain or lose electrons. So, they are called zerovalent.

 

2 Marks Questions

 

1.  Why is position assigned to hydrogen in Periodic Table considered anomalous ?


2.  Some of the element and their atomic numbers are mentioned in the given table.

(i) How many valence electrons are there in the element 'R' ?

(ii) What is the valency of 'P' ?

(iii) Write the chemical formula of the compound formed by combining the elements 'P' and 'Q' ?

(iv) Out of the two elements 'P' and 'S', which one is larger in size ?


3.  State Modern Periodic Law. Name the two elements of first period.


4. Two elements X and Y have atomic number 12 and 16 respectively. Write the electronic configuration of these elements. State the period of these elements. What type of bond will be formed if these two elements combine together ?


5.  "Elements in Periodic Table show periodicity of properties "List any four such properties.


6.  Calcium, magnesium and strontium have been but together in the same group of Periodic Table on the basis of their similar chemical properties.

(i) Mention those properties (Any two)

(ii) Out of the three elements. which one will have atom of biggest size and why ?


7.  (a) State the basis of classification of elements in the Modern Periodic Table.

(b) An element belongs to group 17 of the  Periodic Table, how many electrons does it have in its outermost shell ?


8.  (i) Mention one property each of elements in a group and of elements in a period in Modern Periodic Table.

(ii) What is the number of valence electrons in magnesium and sulphur whose atomic numbers are 12 and 16 respectively ?


9.  The atomic radii of three elements A, B and C of the  Periodic Table are 186 pm, 104 pm and 143 pm respectively. Giving a reason, arrange these elements in the increasing order of atomic numbers in the period.


10.  An elements X belongs to 13th group of the Periodic Table. Find its valency. What will be the formula of its sulphate ?


11.  (i) An atom has electronic configuration 2, 8, 7. What is the atomic number of the element ? To which of the following elements would it be chemically similar ?
[N (7), F (9), P (15), Ar (18) ]

(ii) How would the tendency to gain electrons changes as you go from left to right across a period ?


12.  Out of the two elements X and Y which has bigger atomic radius ? Give reason to justify your answer.

(i) X has atomic number 18 and atomic mass 40.
(ii) y has atomic number 20 and atomic mass 40.


13.  The position of three elements X,Y and Z in the Periodic Table are shown alongside.

Group 1 Group 2
X
Y Z

(i )  Which type of ion – cation or anion, will be formed by element X ?

(ii) Which element – Y or Z, has the atom of comparatively larger size ? Give reason in each case.


14.  (a) How does the tendency to gain electrons change as we go down a group ? Give reason.

(b) A part of the Periodic Table is given alongside. How does the valency very, as we move vertically downward from Li to Fr ? Give reason.

Li Be
Na  
K  
Rb  
Cs  
Fr Ra

15.  (a) Elements F, Cl and Br are in group 17. What is the number  of electrons  in outermost shell of these elements ? Give reason for your answer.

(b) Write down the electronic configuration of Al and Si. Their atomic numbers are 13 and 14 respectively.


16.  There elements X, Y and Z belong to 17th group but to 2nd, 3rd and 4th period respectively.

Number of valence electrons in Y is 7. Find the number of valence electrons in X and Z.


17.  On which side of the Modern Periodic Table, will you find metals ? Are they electropositive or electronegative ? Justify your answer.


18.  'X' is an element with atomic number 20.

(i) Is it a metal or a non - metal ?

(ii) Which of the two 'X' or Mg (with atomic number 12) is more reactive ?

(iii) What is the valency of 'X'

(iv) What will be the formula of its chloride ?


19.  Identify the similarity in the atoms of pairs of elements given below :

(a) Na (At. No.11) and K (At. No. 19)

(b) B (At. No. 5) and C(At. No. 6)


20.  Boron, atomic number  5 and aluminium, atomic number 13 are placed in the same group of the periodic table. Write their electronic configuration. Which of the two will be more electropositive and why ?


21.  The elements of second an third period of the Periodic Table are given below :

Li Be B  C N O F
Na Mg Al Si P S Cl

(a) Which atom is bigger in size Li or Be ? Why ?

(b) Which one element out of those given above is the most metallic and why ?


22.  The atomic number of three elements A, B and C are 11, 14 and 17 respectively.

(a) State the group to which these elements belong in the Modern Periodic Table.

(b) Write the formula of the compound formed when the element B reacts with C.


23.  The following questions refer to the elements of the Periodic Table with atomic numbers 3 to 18.

(a) Which of them are noble gases ?

(b) Which of them are halogens?

(c) Which of them are alkali metals ?

(d) What is the electronic configuration of an element with atomic number 10 ?


24.  Account for the following :

(a) Noble gases are placed in a separate group

(b) All the elements of the same group have similar chemical properties.


25.  Give reasons for the following :

(a) Lithium atom is smaller than sodium atom.

(b) Chlorine (atomic number 17) is more electronegative than sulphur (atomic number 16).


26.  Write the trend of atomic size and metallic character along a group and a period in the Modern Periodic Table.


27.  Why does the chemical reactivity of metals increase on moving down a group ?


28.  Write reason for the following (Number in parenthesis is atomic number of the substance) :

(i) Lithium (3) and sodium (11) are considered as active metals.

(ii) Fluorine (9) is more reactive than chlorine (17).


29.  The elements of the third period of the periodic table are given as below : 

Group → 1 2 13 14 15 16 17 18
Period 3 → Na Mg Al Si P S Cl Ar

i) Out of the above, name the elements which separate metals from non - metals.

Mention the name by which such elements are known as.

(ii) How does the tendency to gain electrons change from Group 1 to Group 17 ? Give reason for your answer.


30.  The atomic number of elements A,B,C,D and E are given below :

Element A B C D E
Atomic No. 7 10 12 4 19

From the above table, answer the following question :

(a) Which two elements are chemically similar ?

(b) Which is an inert gas ?

(c) Which element belongs to 3rd period of Periodic Table ?

(d) Which element among these is a non - metal ?

 

Solutions

 

1.  It is because hydrogen resembles properties of both alkali metals and halogens. In one hand, it can lose one electron like alkali metals, in the other, it forms diatomic molecule like halogens and combines with metals and non  - metals to form covalent compounds


2.  (3), (ii) 1, (iii) PQ (iv) S.


3.  

Element Atomic number
P 3
Q 17
R 13
S 11

- Modern Periodic Law : The properties of elements are the 3 periodic functions of their atomic number.

- Hydrogen and helium.


4.  X : 2, 8, 2

Y : 2, 8, 6

- 3rd period

- Electrovalent / Ionic bond.


5.  (i) Atomic size.

(ii) Valency or combining capacity.

(iii) Metallic property.

(iv) Non - metallic property.


6.  (i) - They have two electrons in their outermost shells.

- They all are metals

(ii) Strontium, because new shells are added when we go down the group.


7.  (a) Atomic number was adopted as the basis of classification of elements.

(b) Seven electrons.


8.  (i) Group : Similar chemical properties.

Period : Atomic size decreases from left to right. Tendency to gain electron increases from left to right. (any one)

(ii) Magnesium (12) : 2, 8, 6.

Valency electrons 6.


9.  - A < C < B.

- Since atomic size generally decreases along a period, so B has the highest atomic number followed by C and A.


10.  - Group is 13. So, the number of valence electrons = (13 – 10 ) = 3.

- Valency = 3

- Formula of its sulphate is X2(SO4)3


11.  (i) Atomic no. 17. It will be similar to F (9) because both have same outer configuration.

(ii) Increases : It is due to decrease in atomic size which leads to an increases in the force of attraction between the nucleus and the electron to be added.


12.  Radius of Y is bigger than that X. In X, the number of shells is two while in Y. it is three.


13.  (i) The valency of X is one. It has tendency to lose one electron. Therefore, X will form cation.

(ii) Y; because atomic radius decreases across a period due to increase in the electrostatic force between electrons and nucleus.


14.  (a) Tendency to gain electrons decreases on moving down a group because with increase in size effective positive nuclear charge decreases.

(b) Valency remains constant as we move downwards. Elements of same group have the same number of valence electrons.


15.  (a) 7, because they are elements of group 17.

(b) Al : 2, 8, 3

Si : 2, 8, 4


16.  It will be 7 in X as well as in Z.

The reason being that number of electrons in outermost shell in the elements in same group is same.


17.  - Metals are in the left side of the Modern Periodic Table.

- They are electorpositive because of their tendency to lose electrons.


18.  (i) 'X' is a metal.

(ii) 'X' is more reactive than magnesium.

(iii) Two

(iv) XCl2


19.  (a) Na : 2, 8, 1

K : 2, 8, 8, 1

Both elements have same valence electron. Therefore, they belong to the same group (number 1).

(b) B : 2, 3

C : 2, 4

Both the elements have two shells, hence they belong to the same period (number 2).


20.  - Electronic configuration of B is 2, 3.

Electronic configuration of Al is 2, 8, 3.

- Al will be more electropositive than B because the effective nuclear charge experienced by valence electrons decreases as they are farther away form the nucleus. So, they can be lost easily.


21.  (a) Li

Reasons : Because as we move down the group, atomic size increases and so tendency to lose electrons increases.


22.  (a) A,B and C belong to group 1, 14 and 17 respectively.

(BC4)


23. (a) Noble gases : Elements having atomic numbers 10 and 18.

(b) Halogens : Elements having atomic numbers 9 and 17.

(c) Electronic configuration of Ne (10) = 2, 8.


24.  (a) Noble gases like helium, neon and argon were discovered very late because they are very inert and present in extremely low concentrations in our atmosphere. Hence, they were placed in a new group without disturbing the existing order.

(b) Thus is because they have same number of valence electrons.


25.  (a) Electronic configuratin of CI is 2, 8, 7 and that of W is 2, 8, 6.

As sulphur is placed before chlorine in the Periodic Table, so it has a bigger size and its tendency to gain electrons is less than chlorine.


26. Trend of atomic size.

Along group – atomic size increases from top to bottom.

Along period – atomic size decreases from left to right.

Trend of metallic character :

Along group – metallic character increases from top to bottom>

Along period – metallic character decreases from left to right.


27.  Down the group, the effective nuclear charge experience by valence electrons decreases because the outermost electrons are farther away from the nucleus. Thus, these can be lost easily. Hence, metallic character increases down a group.


28.  (i) Because they have only one valence electron which they can lose easily and thus show high reactivity.

(ii) The reactivity of non metals depends upon the tendency to gain electrons since fluorine is smaller in size and have more nuclear hold as compared  to chlorine.

Therefore, Fluorine accepts electrons more easily than chlorine.


29. (i) Silicon (Si), metalloid.

(ii) Increases, because as we go from Group 1 to Group 17 , atomic size decreases due to increasing the force of attraction between nucleus and electrons.


30.  (a) C and D.

(b) B

(c) C

(d) A

 

3 Marks Questions

 

1.  (a) An element X has both the shells K and L completely filled with electrons. The elements has atomic number  10. Identify the element X.

(b) In which group of the Periodic Table is this element placed ?

(c) Write  its electronic configuration. What is the valency of the element 


2.  An element Y has a total of three shells, with six electrons in its valence shell.

(1) What will be the atomic number of this element ?

(2) In which period will you find this element ?

(3) Name another element which belongs to the same group as this element.


3.  The position of three element X, Y and Z in the Periodic Table is given below :

Group 16 Group 17
Y
X Z

Giving reason, answer the following question :

(1) Out of Y and Z which element  will be more metallic ?

(2) Will atomic size of Z be smaller or larger than that of X ?

(3) Out of Y and Z which element will be more electronegative ?


4.  An element X is placed in group fourteen and third period of the Periodic Table.

(1) Write the formula of its chloride.

(2) What will be the nature of bonding of the chloride ?

(3) Write the electronic configuration of the element X.


5.  Which of the following elements belong to

(i) same period

(ii) same group ?

Explain giving reason.

Element Atomic no.
A 3
B 11
C 17

6.  Lithium is an alkali metal with atomic number 3 and no. of valence electron is 1. The formula of the hydride of lithium is LiH. Boron and carbon are placed in group 13 and 14 respectively with valence electrons 3 and 4. Write the formulae of the hydrides  of boron and carbon giving reason reason for your answer.


7.  The electronic configuration of an element 'X' is 2, 8, 8, 2. To which

(a) period and

(b) group of the Modern Periodic Table does 'X' belong ? State its valency. Justify your answer in each case.


8.  Four elements P, Q, R and S have atomic number 12, 13, 14 and 15 respectively.

Answer the following questions giving reasons :

(i) What is the valency of Q ?

(ii) Classify these elements as metals and non - metals.

(iii) Which of these elements will form the most basic oxide ?


9.  Atomic radii of the elements of the second period are given below :

Period 2 elements B Be O N Li C
At radii (pm) 88 111 66 74 152 77

(1) Arrange the elements in the decreasing order of their atomic radii.

(2) Identify the element the respectively has (i) largest radius. (ii) smallest radius.

(3) Give reason for variation in atomic radii.


10.  Given below are some elements of the Modern Periodic Table :

4Be, 9F, 14Si, 19K, 20Ca

(i) Select the element that has one electron in the outermost shell and write its electronic configuration.

(ii) Select two elements that belong to the same group. Give reason for your answer.

(iii) Select two elements that belong to the same period. Which  one of the two has bigger atomic size ?


11.  An element has same number of electrons in I and IV shells as in the II and III shells.

(a) Write down the electronic configuration of the element.

(b) Write the group number and period to which it belongs.

(c) What is the valency of the element ?


12.  The elements Li, Na and K, each having one valence electron, are in periods 2, 3 and 4 respectively of Modern Periodic Table.

(a) In which group of the Periodic Table should they be ?

(b) Which one of them has the largest atomic radius ? Give reason to justify your answer in each case.


13.  Atoms of seven elements A, B, C, D, E, F and G have a different number of electronic shells but have the same number  of electrons in their outermost shells. How will the following property vary as we move from A to G ?

(1) Metallic character,

(2) Atomic radii,

(3) Valency.


14.  Atomic number of three elements X, Y and Z are given below :

Element Atomic number
X 4
Y 13
Z 18

Identify the group and period which these elements belong to.


15.  An element Y has a total of three shells with four electrons in its valence shell. Another element X has twice as many electrons in its second shell as in its first shell.

(1) Identify the element Y and X.

(2) Is there any similarity between the element Y and X ? If so what ?


16.  Name two metalloids. Mention the position of metalloids in Periodic Table. Why these elements are called metalloids ?


17.  (a) How does electronic configuration of an atom relate to its position in the Modern Periodic Table ?

(b) Which element has a total of three shells with four electrons in its valence shell ?


18.  Name :

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

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

(c) Three elements with filled outermost shell.


19.  An atom of an element has electronic configuration 2, 8, 1.

(a) What is the (i) atomic number and (ii) valency of this element ?

(b) What is the (i) period and (ii) group of this element ?

(c) To which of the following elements would it be chemically similar and why ?

N (7); F(9); Cl(17); K(19)


20.  An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a compound.


21.  (i) Write the electronic configuration of potassium.

(ii) Predict the number of valance electrons in the atom of Ca.

(iii) What is th number of shells in the atom of Na ?

(iv) Arrange Be, Mg, Ca, Sr in the increasing order of the  size of their respective atoms.

(v) Predict whether Rb is a metal or non - metal.

(vi) Out of Na, Li, Be and Mg which one has biggest atom in size ?


22.  An element A reacts with oxygen to form A2O.

(i) Sate the number of electron in the outermost orbit of A.

(ii) To which group of Periodic Table does A belong ?

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


23.  The electronic configuration of three elements X, Y and Z are given below :

X 2

Y 2, 6

Z 2, 8, 2

(i) Which element belongs to the second period ?

(ii) Which element belongs to the eighteenth period ?

(iii) Which element belongs to the second group ?

(iv) What is the valency of Y ?

(v) Y and Z, are they metal or a non - metal ?


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

Group I II IIII IV V VI VII VIII
Periods                
1                
2     B          
3 A C            

Give reason t explain the following :

(a) Element 'A' is a metal.

(b) Element 'C' has larger size than 'B'

(c) Element 'B' has a valency of 2.


25.  From the part of a Periodic Table, answer the following questions :

1
Hydrogen
2 13 14
Carbon
15 16
Oxygen
17
X           Q
Y           R
Z           T

(a) Atomic number of oxygen is 8. What would be the atomic number of, fluorine ?

(b) Out of 'X' and 'Q' which element has larger atomic size ? Give reason for your answer.

(c) Out of 'Y' and 'Z' which element has smaller atomic size ? Give reason for your answer.


26.  Answer the following questions :

(i) Metals like lithium, sodium, potassium react with water to liberate hydrogen gas. What is the similarity in the atoms of these elements ?

(ii) Which out of the following is having highest metallic character and why ? (Given that Mg and K are on left side in Periodic Table and Cl and P on right Mg, K, Cl, P)

(iii) An atom has electronic configuration 2, 82 7. What is its atomic number ?


27.  The elements of a period of the Periodic Table are given below in order, from left to right with one of its element missing :

Li            Be        B         C        O        F        Ne

(i) To which period do these elements belong ?

(ii) One element of this period is missing. Which is the missing element and where should it be placed ?

(iii) Which one of these elements in this period shows the property of catenation ?

(iv) Which one of the above elements belongs to the halogen series ?

(v) Identify the noble gas.


28.  State Modern Periodic Law. List the characteristics that are determined by knowing the position of an element in the Periodic Table.


29.  The atomic number of nitrogen (N), oxygen (O) and fluorine (F) are , 8 and 9 respectively.

(i) What is the number of valence electrons in N and F

(ii) Name the element having smallest and largest atomic radii of any of the above three elements. Give reason for your answer.


30.  (a) Name an element you would expect to show chemical reactions similar to sodium. State the reason in support of your answer.

(b) Write electronic configuration of the element belonging to 3rd period and 13th group of the Periodic Table. Predict whether it is a metal or a non - metal. give reason.


31.  The elements of the second period of the Periodic Table are given below :

Li, Be, B, C, N, O, F, Ne

(a) Give reason to explain why atomic radius decreases from Li to F.

(b) Identify the most metallic and non - metallic elements.

(c) How does valency change from Li to Ne ?

 

Solutions

 

1.  (a) Element X is neon (Ne).

(b) It is placed in group 18 of the Modern Periodic Table.

(c) - Electronic configuration of neon (Ne) is :

K   L

2    8

- Its valency is zero (0).


2.  (1) The atomic number of 'Y' would be 16 (2 + 8 + 16).

(2 ) 'Y' is placed in 3rd period as it has a total of three shells.

(3) Oxygen (O) / Selenium (Se).


3.  (1) Z is more metallic than Y as elements become more metallic as we go down the group.

(2)  Atomic size of Z is larger than that of X as atomic size increases on going down the group.

(3) Y is more electronegative than Z as electronegativity decreases on going down the group.


4.  (1) XCl4,

(2) Covalent bond,

(3) 2, 8, 4.


5.  (i) Elements B and C belong to the same period in the Periodic Table because both have same number of shells as the electronic configuration of B and C are 2, 8, 1 and 2, 8, 7 respectively.

(ii) Elements A and B belong to same group as both have same number of valence electrons as the electronic configuration of A and B are 2, 1 and 2, 8, 1 respectively.


6.  - Formula of the hydride of boron is BH3.

- Formula of hydride of carbon is CH4.

Reason : The valency of boron and carbon are 3 and 4 respectively as they have and 4 valence electrons an valency of hydrogen is 1.


7.  The electronic configuration of 'X' is given by 2, 8, 8, 2.

(a) As there are four shells in X, it belongs to period 4.

(b) - No. of valence electron in X is 2. Therefore, it belongs to group 2.

- It acquire noble gas configuration by losing 2 electron from its valence shell. Therefore, its valency is 2.


8.  (i) Valency of Q is 3 because it obtains a noble gas configuration by losing its 3 valence electrons as its electronic configuration is 2, 8, 3.

(ii) - Metals : P and Q

- Non - metals : R and S

(iii) Reasons : - The electronic configuration of P and Q are 2, 8, 2 and 2, 8, 3 respectively. So they will tends to lose their valence electrons while forming bonds.

- The electronic configuration of R and S are 2, 8, 4 and 2, 8, 5 respectively. So, they will form bonds by either sharing or gaining electrons.


9.  (1) Li > Be > B C > N > O

(2) (i) Li (Lithium), (ii) O (Oxygen).

(3) Atomic radius decreases on moving from left to right along a period. This is due to an increases in nuclear charge which tends to pull the electrons closer to the nucleus.


10.  (i) - 19K has one electron in its outermost shell.

- Its electronic configuration is 2, 8, 8, 1.

(ii) 4Be and 20Ca belong to the same group because both have 2 valence electrons as their electronic configurations is 2, 8, 8, 1.

(ii) 4Be and 20Ca belong to the same group because both have 2 valence electrons as their electronic configurations are 2, 2 and 2, 8, 8, 2 respectively.

(iii) - 19K and 20Ca belong to the same period because both have 4 shells as their  electronic configurations are 2, 8, 8, 1  and 2, 8, 8, 2 respectively.

- 19K has bigger atomic size than 20Ca


11.  (a) 2, 8, 8, 2

(b) - Group — 2

- Period — 4

(c) 2


12.  (a) Group 1 as each have one valence electron.

(b) Li is the least reactive as reactive increases as we move down the group.

(c) K has the largest atomic radius s atomic radius increases on going down the group.


13.  As all the atoms of seven given elements have same number  of electrons in their outermost shells, they will belong to same group and  hence we move from A to G.

(1) Metallic character increases.

(2) Atomic radii increases.

(3) Valency increases from A to D then decreases to G.


14. 

Element Group Period
X 2 2
Y 13 3
Z 18 3

15.  (1) - 'X' is carbon (C).

- 'Y' is silicon (Si)

(2) Both 'X' and 'Y' have same physical and chemical properties as they belong to the same group.


16.  - Boron (B) and silicon (Si) are metalloids.

- metalloids are found in the middle of the Modern Periodic Table.

- These are called metalloids because they exhibit some properties of both metals and non - metals.


17.  (a) The position of an element can be determined by its electronic configuration. The number of shells present in the atom determines its period and the number of valence electrons determines its group.

(b) Silicon (Si)


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

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

(c) Helium (He), neon (Ne) and argon (Ar).


19.  (a) (i) (ii) 1

(b) (i) 3, (ii) 1.

(c) It will be chemically similar to F(9) and (17) as they belong to the same group.


20.  (a) Write the position of these elements in the Modern Periodic Table as its electronic configuration is 2, 8,7.

- Element Y lies in group 2 and period 4 of the Modern Period 3 of the Modern Periodic Table as its electronic configuration is  2, 8, 8, 2.

(b) YX2. Because the valency of X and Y are 1 and 2 respectively.


21. (i) 2, 8, 8, 1

(ii) 2,

(iii) 3,

(iv) Be < Mg < Ca < Sr,

(v) Metal,

(vi) Na.


22.  (i) A form A2O means two electrons are given to O2 atom by two atoms of A. So, each A atom has one electron in its outermost shell.

(ii) 'A' belongs to 1st - group of Periodic Table.

(iii) 'A' is a metal.


23.  (i) Y,

(ii) X,

(iii) Z,

(iv) 2,

(v) Y : non - metal, Z : metal.


24.  (a) Element 'A' is a metal because it is present in group 1 (1 valence electron) and can lose electron easily.

(b) Element 'C' has larger size than 'B' because it has more number of shells than 'B'

C = period 3 (3 shells)

B = period 2 (2 shells)

(c) 'B' being an element of 3rd group has three valence electrons therefore its valency is 3.


25. (a) 9, because atomic number increases by one in going from one element to the next in Modern Periodic Table.

(b) 'X' because of less effective nuclear charge.

(c) 'Z' has larger atomic size because new shells are added where we go down the group


26.  (i) They have same number of valence electrons.

(ii) K, because metallic character decreases along the period and increases down the group.

(iii) 17.


27. (i) Second period

(ii) Nitrogen and it should be placed in between carbon and oxygen.

(iii) Carbon (C)

(iv) Fluorine (F)

(v) Identify the noble gas.


28.  - The properties of elements are periodic function of their atomic number.

(i) Relative size of atom

(ii) Metallic or non - metallic properties

(iii) Valency

(iv) Nature of their oxides


29.  (i) Valence electrons of N = 5, Valence electrons of F = 7.

(ii) Smallest radius = F, Largest radius = N.

Atomic radius decreases from left to right across a period due to increases in the force of attraction between nucleus and electrons.


30.  (a) Potassium (K). Reason : They have similar electronic configuration.

(b) Electronic configuration : 2 8, 3

It is a metal as it loses three electrons to complete its octet.


31.  (a) Atomic radii decrease on moving from left to right along a period due to increase in nuclear charge which pulls electrons closer to the nucleus and thus reduces the size of the atom.

(b) Li is the most metallic element.

F is the most non - metallic element .

(c) Valency first increases from + 1 to 4 and then decreases from 3 to 0.

 

5 Marks Questions

 

1.  Consider the following elements :

20A; 8B; 18C; 16A; 4A; 2F;

Answer the following giving  reasons :

Which of the above elements you would expect to be :

(i) very stable

(ii) in group 2 of the Periodic Table

(iii) in group 16 of the Periodic Table

(iv) What type of bond will be formed when the element A reacts with B ? Explain


2.  (i) Why do we classify elements ?

(ii) What are the two  criteria used in the development of Modern Periodic Table ?

(iii) State the position (a) metals (b) non - metals, and (c) metalloids in the Periodic Table.

(iv) Would you place two isotopes of chlorine; Cl – 35 and Cl – 37 in different slots of because their chemical properties are same ? Justify your answer.

 

Solutions

 

1.  (i) 18C, as it has completely filled outermost shell.

(ii) 20A, as its electronic configuration is 2, 8, 8, 2.

(iii) 16D, as its electronic configuration is 2, 8, 6.

(iv) Ionic bond as A attains noble gas configuration by losing 2 electrons and B attains of  same by gaining 2 electrons.


2.  (i) We classify elements to study the properties of elements and to keep the elements with similar property together.

(ii) The two criteria used are chemical properties of elements and atomic number.

(iii) Metals are placed on extreme left, metalloids in the middle, non - metals on the right side in the Periodic Table.

(iv) They should be placed in the same place since they have same numbers of electrons.



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