Kerala Syllabus Class 9 Chemistry Chapter 2 Periodic Table Notes Solutions

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Kerala SCERT Class 9 Chemistry Chapter 2 Solutions Periodic Table

Kerala Syllabus Std 9 Chemistry Chapter 2 Periodic Table Notes Solutions Questions and Answers

Class 9 Chemistry Chapter 2 Let Us Assess Answers Periodic Table

Question 1.
The symbols of a few elements are given. Write the electron configurations of these elements and find the period and group to which they belong.
a) \({ }_{11}^{23} \mathrm{Na}\)
b) \({ }_{13}^{27} \mathrm{Al}\)
c) \({ }_{17}^{35} \mathrm{Cl}\)
d) \({ }_{8}^{16} \mathrm{O}\)
e) \({ }_{10}^{20} \mathrm{Ne}\)
f) \({ }_{6}^{12} \mathrm{C}\)
Answer:

Element	Atomic Number	Electron configuration	Period number	Group number
a) \({ }_{11}^{23} \mathrm{Na}\)	11	2, 8, 1	3	1
b) \({ }_{13}^{27} \mathrm{Al}\)	13	2, 8, 3	3	13
c) \({ }_{17}^{35} \mathrm{Cl}\)	17	2, 8, 7	3	17
d) \({ }_{8}^{16} \mathrm{O}\)	8	2, 6	2	16
e) \({ }_{10}^{20} \mathrm{Ne}\)	10	2, 8	2	18
f) \({ }_{6}^{12} \mathrm{C}\)	6	2, 4	2	14

Question 2.
The electron configuration of element X is 2, 8, 8, 1. (Symbol is not real.)
a. Find the atomic number of X.
b. To which group does it belong?
c. What is its period number?
d. To which family does it belong?
e. Write the electron configuration of the noble gas which comes just before X.
Answer:
a. 19
b. Group 1
c. Period 4
d. Alkali metals
e. 2, 8, 8

Question 3.
There are 3 shells in an atom of element P. There are 7 electrons in its outermost shell. (Symbol is not real.)
a. Write the electron configuration of element P.
b. What is its atomic number?
c. To which period does it belong?
d. To which group does it belong?
e. Draw the model of this atom.
Answer:
a. 2, 8, 7
b. Atomic number – 17
c. Period – 3
d. Group – 17
e.

Question 4.
The element M belongs to the 3rd period and group 1. (Symbol is not real)
a. Write the electron configuration of this element.
b. Write its name and symbol.
c. To which family does this element belong?
d. Write the electron configuration of the element belonging to the Same period and group 13.
Answer:
a. 2, 8, 1
b. Sodium, Na
c. Alkali metals
d. 2, 8, 3

Question 5.
Electron configurations of elements P, Q, R and S are given. (Symbols are not real)
P – 2, 7
Q – 2, 8
R- 2, 8, 1
S – 2, 8, 7
a) Which of these elements belong to the same period?
b) Which of these elements belong to the same group?
c) Identify the noble gas among these.
d) Find the group number and period number of element S.
Answer:
a) P and Q, R and S
b) P and S
c) Q (electron configuration: 2, 8)
d) Group number – 17
Period number – 3

Question 6.
Electron configurations of a few elements are given.
A – 2, 1
B – 2, 8, 1
C – 2, 8, 7
(Symbols are not real)
a. Which of these elements has bigger atom, A or B?
b. Which atom is bigger, B or C?
Answer:
a. B
b. B

Question 7.
A portion of the modern periodic table is given. (Symbols are not real) Answer the following questions.

a. Which of these elements belong to the halogen family?
b. Which are the transition elements?
c. Write the elements of group 1 in the decreasing order of their atomic size.
d. Which element has a smaller atom, B or I?
e. Write the elements of period 3 in the increasing order of their atomic size.
f. Which of these are alkaline earth metals?
g. Which element has 8 electrons in its outermost shell?
h. Find the real symbols of the given elements with the help of the periodic table.
Answer:
a. M and N
b. G and H
c. D > C > B > A
d. I
e. N < J < F < C
f. E and F
g. O
h. A – H, B – Li, C – Na, D – K, E – Be, F – Mg, G – Cr, H – Fe
I – B, J – Al, K – N, L – O, M – F, N – Cl, O – Ne

Question 8.
An element belonging to the 2nd period has 2 electrons in the outermost shell of its atom.
a. Write the electron configuration of this element.
b. Write the electron configuration of the noble gas belonging to the same period.
c. What is its group number?
d. Write the electron configuration of an element in the same group and in the third period.
Answer:
a. 2, 2
b. 2, 8
c. 2
d. 2, 8, 2

Question 9.
Analyse the table and answer the following questions.

Element	Mass number	Number of neutrons
A	9	5
B	35	18
C	39	20
D	40	22

(Hint: Symbols are not real)
a. Find the atomic number of these elements.
b. Write their electron configurations.
c. Which among these is a noble gas?
d. To which family does the element B belong?
e. To which period and group does the element C belong?
f. Which of these elements belong to the same period?
Answer:
a. Atomic numbers: A – 4, B – 17, C – 19, D – 18.
b. Electron configurations: A – 2, 2, B – 2, 8, 7, C – 2, 8, 8, 1, D – 2, 8, 8
c. D
d. Halogens
e. Period – 4, Group – 1
f. B and D

Extended Activities

Question 1.
Two English alphabets have not been used as symbols of elements so far. Find them with the help of the periodic table.
Answer:
The letters “J” and “Q” are the only two letters not found on the periodic table.

Question 2.
Prepare the biography of scientists involved in the classification of elements and publish it in the science magazine.
Answer:
Hints
Title: Pioneers of Periodicity
1. Dmitri Mendeleev (1834 – 1907):

• Formulated Periodic Law and created the first periodic table.
• Predicted properties of undiscovered elements.

2. Henry Moseley (1887 – 1915):

• Determined atomic number’s significance in element arrangement.
• Resolved periodic table inconsistencies.

3. Glenn T. Seaborg (1912 – 1999):

• Discovered transuranium elements.
• Proposed modem periodic table layout, including actinides.

Question 3.
Draw a model of the modern periodic table and exhibit it in your classroom.
Answer:
Hints

1. Materials: Poster board, markers, index cards.
2. Layout: Draw a grid with rows (periods) and columns (groups).
3. Element Blocks: Write element symbols and numbers on index cards.
4. Colour Coding: Use different colours for metals, non-metals, and metalloids.
5. Periods and Groups: Label rows 1 – 7 as periods and columns 1 – 18 as groups.
6. Element Placement: Arrange cards by atomic number and properties.
7. Display: Hang the model in the classroom for easy reference.

Question 4.
Prepare a table including the symbol, the electron configuration, and the physical state of elements having atomic numbers 1 to 36, using Kalzium software.
Answer:

Element	Symbol	Electron configuration	Physical state
Hydrogen	H	1	Gas
Helium	He	2	Gas
Lithium	Li	2, 1	Solid

Similarly, complete the table.

Question 5.
Using cardboard pieces, design a periodic table as shown in the figure given in the first page of this unit.
Answer:

• Gather cardboard, scissors, markers, and glue.
• Create a base structure with rows and columns.
• Cut out element tiles and label them.
• Arrange tiles by periods and groups.
• Add transition metals and separate lanthanides/actinides if desired.
• Decorate and label for clarity.
• Glue tiles onto the base.
• Display your cardboard periodic table.

Periodic Table Class 9 Notes Questions and Answers Kerala Syllabus

Question 1.
List the merits of Mendeleev’s periodic table.
Answer:

• Elements are classified in such a way that elements of similar properties were placed in the same group. Thus, learning chemistry was made easier.
• Corrected the wrongly determined atomic masses and gave the correct position to elements.
• Columns were left vacant for elements that were not known at that time, and predicted their properties.

Question 2.
List the limitations of Mendeleev’s periodic table.
Answer:

• Elements with large differences in properties were included in the same group.
• Eg: Hard metals like copper (Cu) and silver (Ag), along with soft metals like Sodium (Na) and potassium (K).
• No proper position could be given to the element hydrogen. Non-metallic hydrogen was placed along with metals like lithium (Li), Sodium (Na) and potassium (K).
• The increasing order of atomic mass was not strictly followed throughout.
• If elements are arranged in the order of atomic mass, isotopes should also be given a position. That was not done.

Question 3.
How do isotopes of the same element differ from one another?
Answer:
Isotopes are the atoms of the same element with the same atomic number and different mass numbers.
Eg: \({ }_{1}^{1} \mathrm{H}\), \({ }_{1}^{2} \mathrm{H}\) and \({ }_{1}^{3} \mathrm{H}\)
You know that elements are arranged on the basis of atomic mass in Mendeleev’s periodic table. Since isotopes have different atomic masses, it is necessary to assign different positions for them in the periodic table.

For example, \({ }_{1}^{1} \mathrm{H}\), \({ }_{1}^{2} \mathrm{H}\) and \({ }_{1}^{3} \mathrm{H}\) are the isotopes of hydrogen. As per Mendeleev’s periodic table, it is not possible to assign a specific position to each of them on the basis of atomic mass.

Through his X-ray diffraction experiments, Henry Moseley proved that the properties of elements depend mainly on atomic number rather than atomic mass. He then revised Mendeleev’s periodic law. This is known as modem periodic law.

Question 4.
How many periods are there?
Answer:
There are seven periods in the modem periodic table.

Question 5.
Write the total number of groups.
Answer:
Eighteen

Question 6.
Which period has the least number of elements?
Answer:
Period 1. (Two elements only: Hydrogen and Helium)

Question 7.
Are the number of elements in periods 2 and 3 the same?
Answer:
Yes (eight elements each)

Question 8.
How many elements are included in the 4th period?
Answer:
Eighteen

Question 9.
What all information about an element can be obtained from the periodic table? Note down in the science diary.
Answer:
Name, Symbol, Atomic number, Mass number, Electronic configuration, Physical state, Group number, Period number.

Question 10.
Elements of group 1 are given in the table. Complete the table

Name of the element	Symbol	Atomic number	Electron configuration
Lithium	Li	3	–
Sodium	Na	11	–
Potassium	–	–	2, 8, 8, 1
Rubedium	Rb	–	2, 8, 18, 8, 1
Caesium	–	55	2, 8, 18, 18, 8, 1
Francium	Fr	–	2, 8, 18, 32, 18, 8, 1

Answer:

Name of the element	Symbol	Atomic number	Electron configuration
Lithium	Li	3	2,1
Sodium	Na	11	2, 8, 1
Potassium	K	19	2, 8, 8, 1
Rubedium	Rb	37	2, 8, 18, 8, 1
Caesium	Cs	55	2,8, 18, 18, 8, 1
Francium	Fr	87	2,8, 18, 32, 18, 8, 1

Question 11.
Have you noticed any peculiarity regarding the number of outermost electrons in the elements of group 1?
Answer:
All elements in group 1 have the same number of outermost electrons.

Question 12.
With the help of the periodic table, write the electron configuration of the elements in group 2.
Answer:

Name of the Element	Symbol	Atomic Number	Electron Configuration
Beryllium	Be	4	2,2
Magnesium	Mg	12	2, 8, 2
Calcium	Ca	20	2, 8, 8, 2
Strontium	Sr	38	2, 8, 18, 8, 2
Barium	Ba	56	2, 8, 18,18, 8, 2
Radium	Ra	58	2, 8, 18, 32, 18, 8, 2

It is clear that the number of outermost electrons of the elements in a given group is the same.The
chemical properties of elements are based on the number of outermost electrons in them. Usually,
these electrons take part in chemical reactions.

Based on the common characteristics of elements in each group, they can be considered as families.
A table enlisting the various families of elements is given below.

Group number	Name of family
1	Alkali metals
2	Alkaline earth metals
From 3 to 12	Transition elements
13	Boron family
14	Carbon family
15	Nitrogen family
16	Oxygen family
17	Halogens
18	Noble gases

Question 13.
Which of these elements are familiar to you?
Answer:
Hydrogen, Nitrogen, Oxygen, Chlorine, Aluminium, Sodium.

Question 14.
Write the examples of metals among these elements.
Answer:
Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, Ga, Sn, Pb etc.

Question 15.
Do these elements include non-metals?
Answer:
Yes. B, C, Si, N, P, O, S, F, Br, He, Ne, Ar etc.

Question 16.
Do these groups include elements belonging to the solid state, liquid state and gaseous state?
Answer:
Solids: – Li, Na, K, Rb, Be, Mg, Ca, Sr, Ba, Ra, B, Al, In, Tl, C, Si, Ge, Sn, Pb, S, Se, Te, Po, I, At
Liquids:- Cs, Fr, Hg, Ga, Br
Gases:- H, N, O, F, Cl, He, Ne, Ar, Kr, Xe, Rn

Question 17.
How does electron filling take place in the outermost shell of these elements?
Answer:
From left to right, with an increase in atomic number, the number of electrons in the outermost shell increases by one.

Question 18.
What change do you observe in the number of outer electrons on moving from left to right along a period?
Answer:
On moving along a period from left to right, there is an increase of one electron in the outermost shell of the main group elements until eight electrons are gained.

Question 19.
Which are the families included in the main group elements?
Answer:
Alkali metals, Alkaline earth metals, Boron family, Carbon family, Nitrogen family, Oxygen family, halogens and noble gases.

Question 20.
In which groups are metalloids present?
Answer:
The metalloids are found in a zig-zag arrangement in the periodic table between group 13 and group 17.
They are found between the metals and non-metals in the periodic table.
Eg: silicon is in group 14 along with germanium, whereas arsenic belongs to group 15.

Question 21.
A few elements of groups 1 and 2 are given in the Table below.
Complete the table and record it in your science diary.

Answer:

Question 22.
What is the relation between the number of outermost electrons and the group number here?
Answer:
Both are same.
In the elements of groups 1 and 2, the number of outermost electrons represents the group number
Let us examine whether groups 13 to 18 follow the same relation.

Question 23.
Complete the Table on the basis of the periodic table.

Answer:

Question 24.
Find the number that is added to the number of outermost electrons to get the group number of elements in groups 13 to 18.
Answer:
10

Question 25.
Have you ever thought why the number 10 is added to the number of outermost electrons?
Answer:
Between 2 and 13 groups of elements, 10 groups of transition elements are included.

Question 26.
In how many groups are they distributed?
Answer:
From 3 to 12
The position of transition elements is after the second group elements in the periodic table. The elements from groups 13 to 18 are placed after these 10 groups of transition elements.
It is clear why the number 10 is added to the number of outermost electrons to get the group number of groups 13 to 18.

Question 27.
Complete the Table with the help of the periodic table.

Answer:

Question 28.
Can you find any relation between the period number and the number of shells of the given elements?
Answer:
In these elements, the number of shells is the period number.
The number of shells in the atoms of elements is their period number

Question 29.
Certain data regarding the main group elements are given in the following table. Complete the Table and record it in your science diary.

Answer:

Question 30.
You know that the elements given in the table are noble gases. To which group do they
belong?
Answer:
Group 18

Question 31.
What peculiarity do you notice in the number of the outermost electrons of elements except helium?
Answer:
All elements have 8 electrons in the outermost shell except helium.
If elements other than hydrogen and helium have 8 electrons in their outermost shell, they attain . stability. It is to attain this stability that atoms of all elements undergo chemical reactions. (You can leam more about this in the next unit.)

Usually, 18th-group elements do not take part in chemical reactions because of the stable arrangement of electrons.

Question 32.
Elements ₈P, ₁₀Q, ₁₂R, ₁₈S are given, (symbols are not real)
a) Write down the electron configuration of these elements.
b) Which among these are noble gases?
Answer:
a) P : 2, 6
Q : 2, 8
R : 2, 8, 2
S : 2, 8, 8

b) Q and S

Question 33.
Which transition elements are familiar to you? List them with the help of the periodic table.
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Answer:
Iron, copper, zinc, silver, mercury etc.

Question 34.
Are all of them metals?
Answer:
Yes. All of them are metals.

Question 35.
From which period onwards can you locate transition elements in the periodic table?
Answer:
From the fourth period.

The elements of groups 1 and 2 are generally more metallic in nature and are placed on the left side of the periodic table. Meanwhile, the elements from groups 13 to 18 are placed on the right side, of the periodic table and are generally less metallic in nature. Based on this, how will you indicate the position of the transition elements?

The transition elements lie in between the more metallic elements and the comparatively less metallic ones.

The elements from group 3 upto group 12 are known as the transition elements because they indicate a regular change or transition from more metallic elements of group 2 to less metallic elements of group 13
Let us consider another peculiarity of the transition elements. The electron configuration of a few elements in the 4th period is given in the Table below

It is evident from the table that in the elements of group 1 and 2, the electron is being added to the last shell.

However, in groups 3,4 and 5, electrons are being added to the penultimate shell.

In ten groups from group 3 to 12 (transition elements), electron filling takes place in the penultimate shell.

You have learnt that elements in the same group show similarity in properties.
Generally, transition metals also show such similarity in groups.
Let us examine whether they exhibit any peculiarity along a period.

Question 36.
Analyse the transition elements of the 4th period given in the Table above.
Do they have any peculiarity in the number of outermost electrons?
Answer:
They have the same number of outermost electrons.
Usually, transition elements in the same period have the same number of outermost electrons. Hence,they show similarity in properties along a period too.

Question 37.
You have seen coloured chemicals in your lab. Examine the chemicals given in the Table given below. Find their molecular formulae and identify their colours with the help of your teacher. Complete the table and record it in your science diary.

Answer:

Name of the chemical	Molecular formula	Colour
Nickel sulphate	NiSO4	Bluish green
Copper sulphate	CuSO4	Blue
Calcium carbonate	CaCO3	No Colour
Potassium permanganate	KMnO4	Pink
Cabolt nitrate	CO(NO3)2	Blue
Potassium diehromate	K2Cr2O7	Orange
Ferrous sulphate	FeSO4	light green

It is clear that transition elements are present in the coloured compounds given in the table.Usually,
transition elements form coloured compounds.

• Elements included in groups 3 to 12 are transition elements.
• The filling of electrons takes place in the penultimate shell.
• Generally, they exhibit similanty in chemical properties in groups as well as in periods.
• They are metals.
• They generally form coloured compounds.

Question 38.
Have you noticed the number of elements included in the 6th period of the periodic table?
Answer:
18

Question 39.
Identify the position of lanthanum (atomic number -57) and the 14 elements following it.
Answer:
They are placed just below the main body of the periodic table as the first row.

Question 40.
Similarly, find the position of actinium (atomic number-89) and the 14 elements following it in the 7th period.
Answer:
They are placed just below the main body of the periodic table as the second row.

In the 6th period, lanthanum and the 14 elements following it, have been arranged separately at the bottom of the periodic table. The elements from lanthanum, (La, atomic number – 57) to lutetium (Lu, atomic number – 71) are known as lanthanoids.

In the 7th period, actinium and the 14 elements following it have ’been given a separate position below lanthanoids. The elements from actinium (Ac, atomic number – 89) to lawrencium (Lr, atomic number – 103) are called actinoids.

Lanthanoids and actinoids are known as inner transition elements. Lanthanoids are also called rare earths. Actinoids coming after uranium (U) are man-made elements.

Question 41.
You are familiar with situations in which transition elements and their compounds are used in our daily life. What are they?
Answer:

• All transition elements are useful metals.
• They are used to make alloys.
• Compounds of transition elements are used for adding colour to glass, fireworks etc.
• Transition elements and their compounds are used as catalysts.

Transuranium Elements

All the 118 elements discovered till now are included in the modem periodic table. Among elements from atomic number 1 to 92, the elements except technitium (atomic number 43) and promethium (atomic number 61) are naturally occurring. Elements coming after atomic number 92 are made artificially. Artificial elements are less stable and exhibit radio activity.
The elements coming after uranium (atomic number – 92) are known as transuranium elements

Question 42.
What change do you observe in the number of shells, on moving down the group?
Answer:
The number of shells increases.

Question 43.
How does the increase in the number of shells influence the size of an atom?
Answer:
When the number of shells increases, the size of the atom also increases.The nuclear charge depends on the number of protons present in the nucleus.

Question 44.
What change do you observe in the number of protons with the increase in the atomic number?
Answer:
Increases

Question 45.
If so, what happens to the nuclear charge with the increase in the atomic number?
Answer:
Increases
With an increase in nuclear charge, the force of attraction between the nucleus and the outermost electron increases.

Question 46.
If so, what happens to the size of the atom? Why?
Answer:
Size of atom decreases.
Because when nuclear charge increases, the attraction of nucleus on electrons increases.
Though nuclear charge increases down a group, its effect is overcome by the increase in the number of shells and hence, the size of the atom increases.
Though nuclear charge increases down a group, its effect is overcome by the increase in the number of shells and hence, the size of the atom increases.
The electron configuration of the elements belonging to the 2nd period of the periodic table is given below.

Question 47.
Do you observe any change in the number of shells on moving along a period from left to right?
Answer:
No

Question 48.
Does the nuclear charge increase?
Answer:
Nuclear charge increases on moving along a period from left to right, but there is no change in the number of shells.

Question 49.
What happens to the attractive force of the nucleus towards the outermost electrons? (increases/ decreases)
Answer:
Increases

Question 50.
What change takes place in the size of the atom?
Answer:
The size of the atom will decrease.
Moving along a period from left to right, there is no change in the number of shells. But nuclear charge increases gradually. The attractive force of the nucleus on the outermost electron increases. Hence, the size of the atom gradually decreases.

Screening Effect (Shielding Effect)
The number of shells increases down a group. As a result, the outermost electrons move away from the nucleus. As the number of electrons in the inner shells increases, the attractive force of the nucleus on the outermost electrons decreases gradually. This is known as the screening effect.
You have seen the change in the size of the atom in group and period.

Question 51.
If so, where can you locate the comparatively bigger atoms in the periodic table?
Answer:
Left bottom area

Question 52.
Where are the smaller atoms located?
Answer:
Right top area
Moving down the group, the size of an atom increases. The size of an atom decreases on moving from left to right along a period.
You will learn about periodic trends, such as ionisation energy, electronegativity etc in the next unit.