Kerala SSLC Class 9 Solutions for Physical Sciences – Periodic Table and the Chemical Bond

Kerala SSLC Class 9 Solutions for Physical Sciences – Periodic Table and the Chemical Bond (English Medium) Part-1

Page No. 25:

Question 1:

• What are the constituent elements of sugar?
• Similarly, what are the other compounds in which the constituent elements are familiar to you? Fill up the table.
  

  Compound	Constituent elements
  Water	……………………………
  ……………………………	……………………………
  ……………………………	……………………………

Solution:

• Carbon, hydrogen and oxygen are the constituent elements of sugar.

• Compound	Constituent elements
  Water	Hydrogen, Oxygen
  Baking soda	Sodium, Carbon, Hydrogen, Oxygen
  Washing soda	Sodium, Carbon, Oxygen
  Marble	Calcium, Carbon, Oxygen
  Sand	Silicon, Oxygen
  Salt	Sodium, Chlorine

Question 2:

• How many elements were tabulated in the modern periodic table?
• In how many ways were they classified?
• Are the majority of them metals or non-metals?

Solution:

• 118 elements were tabulated in the modern periodic table.
• Elements are mainly classified into metals, non-metals and metalloids and are further classified as solids, liquids and gases.
• Most of the elements are metals in the periodic table.

Page No. 26:

Question 1:

You have learned the common characteristics of metals and that of non-metals. What are they? Try to recollect.

Solution:

Common characteristics of metals:

• Malleable, i.e. metal can be beaten into thin sheets with a hammer
• Ductile, i.e. metal can be drawn (or stretched) into thin wires
• Contains a single atom (monatomic)
• Good conductors of heat and electricity
• Lustrous or shiny
• Generally hard and strong
• Have high melting points and boiling points
• Solids at room temperature

Exceptions:

• Zinc is non-malleable and non-ductile.
• Mercury is a liquid metal at room temperature.
• Tungsten is a poor conductor of electricity.
• Sodium and potassium are not hard. They are so soft that they can be easily cut with a knife.

Common characteristics of non-metals

• Do not conduct heat and electricity
• Neither malleable nor ductile
• Contains two kind of atoms (monatomic or diatomic).
• Bad conductors of heat and electricity
• Not lustrous
• Generally soft
• Mostly not strong and are easily broken
• May be solid, liquid or gases at the room temperature
• Have low densities, i.e., non-metals are light substances
• Have different colours
• Have comparatively low melting points and boiling points.

 Exceptions:

• Carbon fibre is ductile but not malleable.
• Graphite is a good conductor of electricity.
• Iodine and graphite are lustrous.

It is the distinct differences in properties of elements that have led to their classification into various groups.

Page No. 29:

Question 1:

From among the elements familiar to you, where do you find those with similar properties in groups or in periods?

Solution:
Elements with the similar properties are located in groups

Question 2:

Why has the name ‘Periodic Table’ been given to the table of elements? Think of it in relation to the periodic law.

Solution:
The properties of elements depend on their atomic masses. When the elements are arranged in the increasing order of their atomic mass; their properties repeat after regular intervals. This was termed as ‘periodicity’ of the elements. The elements showing periodicity were arranged in a table format. Hence, the name ‘Periodic Table’ was given to the table of elements.

Page No. 30:

Question 1:

• Did Mendeleev strictly adhere to the ascending order of atomic masses in his periodic table?
• Examine Co, Ni, Te, and I

Co 58.93

Ni 58.69

Te 127.6

I 126.9

Why was the ascending order not followed?

Solution:

• No, Mendeleev didn’t adhere to the ascending order of atomic masses in his periodic table
• The ascending order was not followed because more importance was given to the placing of elements with similar properties in the same group than to the ascending order of their atomic masses. 

page No. 32:

Question 1:

Examine the modern periodic table and find out the following.

• How many periods are there?
• How many groups are there?
• Compare the modern periodic table with Mendeleev’s periodic table. What similarities and differences can you find? Make a note and present it in the class.

Solution:

• There are total 7 periods in the modern periodic table.
• There are total 18 groups in the modern periodic table.
• Modern periodic table is lengthy. But Mendeleev’s periodic table is very short. So Mendeleev’s periodic table is known as short form periodic table and modern periodic table is known as long form periodic table.Mendeleev arranged the elements in the ascending order of their atomic mass. But, in the modern periodic table, the elements are arranged in the ascending order of their atomic number.

Page  No.33:

Question 1:

Look at the portion of the periodic table given.

• In each period, as the atomic number increases, does the number of valence electrons increase?
• At fixed intervals, does the distribution of electrons in the outermost shell get repeated?
• Write the electron distribution of elements in groups 1 and group 2 in table.

• What peculiarity do you see in the number of valence electrons of the elements in the same group?
• Does this apply to also? Examine.
• If so, what could be the elements in the showing similar other groups the reason for same group properties? Discuss and note in the science diary.

Group 1	Group 2
H ………………
Li ………………	Be ………………
Na ………………	Mg ………………
K ………………	Ca ………………

• What peculiarity do you see in the number of valence electrons of the elements in the same group?
• Does this apply to also? Examine.
• If so, what could be the elements in the showing similar other groups the reason for same group properties? Discuss and note in the science diary.

Solution:

• In each period, as the atomic number increases the number of valence electrons also increases.
• Yes, after fixed intervals, the distribution of electrons in the outermost shell gets repeated.
  

  Group 1	Group 2
  H 1
  Li 2, 1	Be  2, 2
  Na 2, 8, 1	Mg  2, 8, 2
  K  2, 8, 8, 1	Ca  2, 8, 8, 2

• The number of valence electrons of the elements that come in the same group are equal.
• This is applicable to all elements that come under the main group.

Science Diary

• The elements in the same group show similar properties because the number of valence electrons is equal down the group and the general electron structure is also the same.
• Since elements in a group show similar properties, the groups are termed as element families.

Question 2:

Note down the number of valence electrons in each group in table.
Can you find any relationship between the group number and the number of valence electrons?

Group Number	Name of the Element Family	Number of valence electrons	Valency
1	Alkali metal family	1	1
2	Alkaline earth metal family
13	Boron family
14	Carbon family
15	Nitrogen family
16	Oxygen family
17	Halogen family
18	Noble gas family

Solution:

Group Number	Name of the Element Family	Number of valence electrons	Valency
1	Alkali metal family	1	1
2	Alkaline earth metal family	2	2
13	Boron family	3	3
14	Carbon family	4	4
15	Nitrogen family	5	3
16	Oxygen family	6	2
17	Halogen family	7	1
18	Noble gas family	8	0

• Yes there is a relationship between the group number and the number of valence electrons.
• In group 1 and 2, number of valence electrons is equal to the group number.
• When elements 13, 18 and 10 is added to the valence electrons, we get group number.
• We can find the group number and valency by knowing the number of valence electrons in that element.
• Valency is the number of electrons gained or lost by the atom of the element to complete its octet.

Question 3:

What does an atom having two electrons in its outermost shell do to attain stability? (✓) whichever is applicable.
□Donates two electrons.
□Accepts two electrons.
□Donates one electron.
□Accepts one electron.

Solution:
✓Donates two electrons.
□Accepts two electrons.
□Donates one electron.
□Accepts one electron.

Page No. 34:

Question 1:

Valency is the number of electrons donated, accepted or shared in this manner.
What about an atom having seven electrons?
Solution:
An atom having seven electrons will accept one electron to complete its octet.

Question 2:

Let the atomic number of element ‘X’ be 6. If so, find out the details given below. (‘X’ is not the correct symbol of the element.)
Electronic configuration ……………….
Group number ……………….
Valency ……………….

Solution:
Electronic configuration 2, 4
Group number 14
Valency 4

Question 3:

Which are the groups not included in following table? Examine.

Group Number	Name of the Element Family	Number of valence electrons	Valency
1	Alkali metal family	1	1
2	Alkaline earth metal family	2	2
13	Boron family	3	3
14	Carbon family	4	4
15	Nitrogen family	5	3
16	Oxygen family	6	2
17	Halogen family	7	1
18	Noble gas family	8	0

Solution:

• Group 3 to 12 are not included in the table.
• The elements of the families included in the given table are called representative elements.
• Some of their characteristics are:
  a. These elements show periodic repetition of electronic configuration.
  b. There are elements belonging to different categories like metals, non-metals and metalloids.
  c. These are a representation of elements in various physical states.
  d. Similar properties are exhibited within the group.
• The elements of groups 3 to 12 are called d-block elements or transition elements.
• The elements located at the left side of the periodic table are metals (s-block elements) and those located at the right side are non-metals (p-block elements). The position of transition elements (d-block elements) is in between s-block and p-block.
• They are called as transition elements because they indicate a gradual progressive change or transition from metallic properties to non-metallic properties.

Question 4:

If you examine the periodic table you will find that they are all metals, How many of them are familiar to you? Write down.

Solution:
Manganese, iron, copper, zinc, nickel, cobalt, silver, mercury, gold, platinum, chromium, cadmiu

Question 5:

Examine the modern periodic table and fill up the following table:

Period number	Number of elements in each period	Which are the shells in the atoms in each period	Total number of shells
1	2	K	1
2	8	K, L	2
3
4
5

• Which is the smallest period? What are the elements present in it?
• What is the relationship between the period number and the number of shells?
• Observe the last elements of all the periods. What is peculiar about them?
• See the sixth and seventh periods. Are the 14 elements coming after lanthanum (₅₇La), in the sixth period, arranged in the same row?
• Similarly, in the seventh period, what about the elements coming after actinium (₈₉Ac)?

Solution:

Period number	Number of elements in each period	Which are the shells in the atoms in each period	Total number of shells
1	2	K	1
2	8	K, L	2
3	8	K, L, M	3
4	18	K, L, M, N	4
5	18	K, L, M, N, O	5

• First period is the smallest period. There are 2 elements hydrogen and helium in the first period.
• The number of shells in the atom of the elements and the number of their period are the same. i.e., in the elements of the 1^st period, there is K shell only. Like this, the elements in the 2^nd period have two shells (K and L) and the elements of the 3^rd period have three shells (K, L and M) and so on. In this way, the number of shells increases with an increase in the number of period.
• Each period ends in a noble element. They have completely filled outermost shells. i.e., their outermost shells have 8 electrons. So the valency will be zero.
• No. Even though the sixth period contains 32 elements, all of them are not arranged in the same row. After including 18 elements in the periodic table, the remaining 14 elements are arranged at the bottom of the table. They are called actinides or f-block elements.
• The seventh period is incomplete. Some elements in this period are not discovered. From this, 14 elements are taken outside and are arranged at the bottom of the table in actinides row (f-block).Lanthanides are a total 14 elements which starts from the element lanthanum in the 6^th period of the periodic table.This lanthanides and actinides are generally termed as the inner transition elements. Most of the actinides are artificial elements.If these elements would have been placed in the main table then the study of the periodic table would have been lengthier.
• The lanthanides and actinides are arranged at the bottom of the periodic table and not in the main table in order to preserve the structure of the table.
• The 14 elements which starts from actinium in the 7^th period of the periodic table are known as actinides.

Page No. 35:

Question 1:

Can you predict the position of an element in the periodic table and its properties by knowing only the atomic number? As an example, write down the characteristics of the element having atomic number 17.

• Electronic configuration ……………………………
• Period number ………………………………
• Group number ……………………………………
• Element family ………………………………….
• Valency ……………………………………….
• Metal or non-metal ………………………………….
• Charge of ion ……………………………………..

Solution:

Yes. We can predict the position of an element in the periodic table and its properties by knowing only the atomic number.
The characteristics of the element having atomic number 17 will be:

• Electronic configuration – 2, 8, 7
• Period number – 3
• Group number – 17
• Element family – Halogen
• Valency – 1
• Metal or non-metal – Non-metal
• Charge of ion – Negative charge
• Element – Chlorine

Question 2:

Can you find out?
Given below is the distribution of electrons of elements A, B, C, and D. (The symbols are not real).
A – 2, 2
B – 2, 8, 2
C – 2, 8, 5
D – 2, 8

• Which are the elements coming within the same period?
• Which are the ones coming within the same group?
• Which is the noble element?
• To which group and period does element C belong?

Solution:

• B and C A and DThis is because they have same number of shells. The number of shells remains same across the periods.

• A, B
• D
• Group – 15 Period – 3

Question 3:

You know that atoms are sub microscopic particles. Do atoms of all elements have the same size? Analyse the Bohr models of atoms from the given illustration.

• As you go down a group, what is the change noticed in the number of shells?
• Is the size of the atom likely to increase or decrease accordingly?
• Does this trend continue in other groups also? Examine the distribution of electrons and note down.
• In each group, where is the biggest atom found – at the top or at the bottom?

Now let us analyse the trend in periods.

• What is the change in the positive charge of the nucleus as you go from left to right in a period?
• Does the number of shells increase?

The Bohr models of the elements in the 1^st group and the 2^nd period in the periodic table are given in the illustration. (fig.)

• Is the ‘L’ shell of Be likely to contract or expand more compared to that of Li?
• In each period, where will the largest atom be – extreme left or right?

Solution:

• As we go down the group, the number of shells increases.
• The size of an atom increases with an increase in the number of shells.
• In other groups also, the size of atom increases while going down the group.
• The biggest atom is found at the bottom of the group.
• On moving from left to right in a period table, the number of protons increases. Therefore, the positive charge of the nucleus increases.
• The number of shells does not change.

The Bohr models of the elements in the 1^st group and the 2^nd period in the periodic table are given in the illustration. (figure)

• The ‘L’ shell of Be is likely to contract more as compared to that of Li. This is because on moving from left to right across the period nuclear charge and its attraction increases.Reason:In case of lithium, the atomic number is 3. It is present in the 2^nd period. The outermost electron is present in the ‘L’ shell i.e. 2^nd shell. This electron is attracted by the 3 positive charges in the nucleus.For other elements other than lithium of the 2^nd period, the outermost electrons continue to be in the ‘L’ shell. Therefore, as one goes from left to right in the period, the size of the atom decreases because of the increase in the attraction of the nucleus due to increase in the nuclear charge.
• In the case of beryllium, the atomic number is 4. The outermost electrons are present in the ‘L’ shell. There are 4 positive charges in beryllium nucleus.
• As the positive charge of the nucleus increases the electrons present in the shells will get attracted more towards the nucleus.

• The largest atom will be on the left side of the periodic table.

Page No.37:

Question 1:
You have learned that the majority of the elements are metals. On which side of the periodic table are these arranged?
Metals ……………………………….
Non-metals …………………………………..
Solution:
Metals are present on the left side and non-metals are present on the right side of the periodic table.
Question 2:
Among metals and non-metals, which one shows the tendency to accept electrons? Think about this in relation to electron distribution and stability. What is the conclusion that can be reached?
(✓) the appropriate.
□Metals generally accept /donate / share electrons.
□ Non-metals generally accept/donate / share electrons.

Solution:
□ Metals generally accept /donate / share electrons.
□ Non-metals generally accept/donate / share electrons.
Metals generally donate electrons.
Non-metals generally accept electrons.

Question 3:

• As the size of the atom increases, will the attraction of the nucleus on the outer most electrons increase or decrease?
• For the larger atoms, which tendency is greater-to donate electrons or to accept electrons?
• What about the smaller atoms?

Solution:

• As the size of the atom increases, the attraction of the nucleus on the outer most electrons decreases.
• For the larger atoms, the tendency to donate electrons is greater.
• For the smaller atoms, the tendency to accept electrons is greater.

Question 4:
Among the atoms of metals, is the electropositive character more for the larger atom or the smaller atom?
Solution:
The electropositive character is found more in larger atoms than in smaller atoms.

Question 5:
In each group and each period, what will be the trend in the electropositive or metallic character?

• Going downward in each group
• Going from left to right in each period

Solution:
Going downward in each group
The electropositive nature of the atoms increases because the size of the atoms increases.
Going from left to right in each period
Since the size of the atoms decreases, the attraction of nucleus on the electrons will be greater. So the electropositive character decreases.
Non-metals are generally of electronegative character. As the size of the atom decreases electronegativity increases.

Page No.38:

Question 1:
In the periodic table, what will be the trend in the electronegative character?
Going downward in the group
Size of the atom ………………………
Electronegativity ………………………
Going from left to right in a period
Size of the atom ………………………
Electronegativity ………………………
Solution:
Going downward in the group
Size of the atom increases
Electronegativity decreases
Going from left to right in a period
Size of the atom decreases
Electronegativity increases
Question 2:
On which side of the periodic table are the elements with more of electronegative character to be found bottom left or top right?
Solution:
In the periodic table, the elements with more of electronegative character is located in the top right of the periodic table.
Question 3:

Given below is an incomplete form of the periodic table. What are given in the cells are not exact symbols of the elements. Try and find out the following, in relation to the position of the elements.

• Which is the smallest atom in the 2^nd period?
• Which is the element with the highest electropositive character?
• Which are the transition elements?
• Which are probably metalloids?
• Which is the element having the highest electronegativity?
• Which one has the highest metallic character?
• Which element has a valency of 4?
• The element with five valence electrons?

Solution:

• J is the smallest atom in the 2^nd period.
• D is the element with the highest electropositive character.
• Elements E and F are the transition elements.
• Elements G and I are the metalloids.
• Element J is the element having the highest electronegativity.
• Element D has the highest metallic character.
• Element H has a valency of 4.
• Element I is the element with five valence electrons.

Question 4:
Given below is an extract from the periodic table

3 Li	4 Be	5 B	6 C	7 N	8 O	9 F
11 Na	12 Mg	13 Al	14 Si	15 P	16 S	17 Cl

• Which molecules formed by combination of the elements in this table are you familiar with? Add more to the list.O₂, P₄, NaCl, Cl₂, MgO, Na₂CO₃, F₂, …………………………………..

• Among these which are the molecules of elements? (✓) them.
• Give a practical definition for chemical bonding. Note it in the science diary.

Solution:

• Na₂O, MgCl₂, N₂, NaF, OF₂, CCl₄, NO₂
• O₂, P₄, F₂, Cl₂, N₂ are the molecules of elements.
• Science DiaryThe electrostatic force of attraction which holds the constituent atoms together in a molecule is known as chemical bonding.

Page No.39:

Question 1:

• In the table which are the elements having high electropositive character?
• Which are the ones having high electronegative character?

3 Li	4 Be	5 B	6 C	7 N	8 O	9 F
11 Na	12 Mg	13 Al	14 Si	15 P	16 S	17 Cl

Solution:

• Li, Na, Be, Mg, AI are the elements having high electropositive character.
• O, S, F, CI, P, N are the ones having high electronegative character.

Question 2:

Let us see how sodium fluoride is formed. Write down the electron distribution of Na and F and draw the Bohr model.

Element
Electron distribution
Bohr model

Solution:

Question 3:

When the two elements combine and produce the more stable NaF, what are the changes that take place?
For Sodium

• Electron (e^‒) …………………….. (Accepts / Donates)
• …………………… ion is produced.

How is this represented?
For Fluorine

• Electron ……………….. (Accepts /Donates)
• ………………. ion is produced.

Complete the equation.

Solution:

For Sodium

• Donates electrons.
• Positive ion is produced.

For Fluorine

• Accepts electron.
• Negative ion is produced.

Page No.40:

Question 1:

• Analyse the possibility of chemical bonding between magnesium and fluorine by writing down the electron distribution of both the elements.
• How many fluorine atoms are required to combine with one magnesium atom?
• What will be the chemical formula of magnesium fluoride?

Solution:
The atomic number of magnesium is 12. Its electronic configuration is 2, 8, 2. It has 2 valence electrons. A magnesium atom donates its 2 valence electrons (to fluorine atoms) in order to achieve stable octet and forms a stable magnesium ion, Mg²⁺.
Mg ‒ 2e^‒ → Mg²⁺
2, 8, 2    2, 8
The atomic number of fluorine is 9. Its electronic configuration is 2, 7. Fluorine atom has 7 valence electrons. So it will require 1 more electron to complete its octet. Since one magnesium atom donates 2 electrons, so two fluorine atoms take these two electrons from the magnesium atoms respectively and form two fluoride ions.
The Positively charged magnesium ions and negatively charged fluoride ions are held together by electrostatic force of attraction to form magnesium fluoride compound.

• Two fluorine atoms are required to combine with one magnesium atom.
• The chemical formula of magnesium fluoride will be MgF₂.

Question 2:

Between which type of elements given below is ionic bond possible?
(✓) the correct answer.
□Electropositive + electropositive
□ Electropositive + electronegative
□ Electronegative + electronegative
Solution:
□ Electropositive – electropositive
✓ Electropositive + electronegative.
□ Electronegative + electronegative

Question 3:

From the molecules you had listed earlier, (by utilizing the given table) write down those forming ionic bonds.

3 Li	4 Be	5 B	6 C	7 N	8 O	9 F
11 Na	12 Mg	13 Al	14 Si	15 P	16 S	17 Cl

NaCl, MgCl₂, …………, …………, …………
Solution:
NaCI, CaCI₂, MgO, NaF, MgCI₂.
Question 4:
Na + F₂ → NaF
Examine whether this is true in the equation written above.

Element	Number of atoms in the reactants	Number of atoms in the products
Na	1	……………….
F	2	……………….

Solution:

Element	Number of atoms in the reactants	Number of atoms in the products
Na	1	1
F	2	1

Page No.41:

Question 1:

The chemical formula for sodium oxide is Na₂O. Look at the equation for its formation.
Na + O₂ → Na₂O

• Is this a balanced equation? If not how can it be balanced?
• Which are the ions in Na₂O?

Solution:

• It is not a balanced equation. Check whether the number of atoms of the elements on the left side of the arrow sign is equal.We can write the equation given as follows to get the number of atoms of oxygen on the right side as 2.Then the number of sodium atom will be 4. To balance this 4 sodium atoms are given on the left side.
• 4Na + O₂ → 2Na₂O
• Na + O₂ → 2NaO

• Sodium ionOxide ion

Question 2:
Given below are the equations for the formation of some ionic compounds. Are they all balanced chemical equations? Can’t you balance those which are not?
Na + Cl₂ → NaCl
Mg + F₂ → MgF₂
Mg + O₂ → MgO
Ca + O₂ → CaO
Solution:
All the given equations are not balanced.
The balanced chemical equations are as follows:
2Na + Cl₂ → 2NaCl
Mg + F₂ → MgF₂ This equation is already balanced.
2Mg + O₂ → 2MgO
2Ca + O₂ → 2CaO
Question 3:
You know that there are diatomic molecules among elements. Try to list those you know.
Cl₂, O₂, F_2, …………, …………, …………
Solution:
Cl₂, O₂, F_2, N₂, H₂
Question 4:
Is the chemical bond in fluorine molecule formed by electron transfer?
Solution:
No. The chemical bond in fluorine molecule is formed by sharing of electrons.
Question 5:
The chemical bonding in Cl₂ molecule can also be indicated like this.
Solution:

Question 6:

• Look at the covalent bond in the O₂ molecule. How many electrons are there in the outer most shell of an oxygen atom

• How many pairs of electrons are shared?

Solution:

• Six electrons are there in the outer most shell of an oxygen atom.
• Two pairs of electrons are shared between the oxygen atoms forming a double bond.

Question 7:

• When a single bond is formed, how many pairs of electrons are there in the bond?
• What about the double bond?
• Formulate definitions for single bonds.

Solution:

• When a single bond is formed, one pair of electrons is there in the bond.
• When double bond is formed, two pairs of electrons are there in the bond.
• The covalent bond formed between the two atoms by the sharing of one pair of electrons is called single bond.
  The covalent bond formed between two atoms by the sharing of two pairs of electrons is called double bond.The covalent bond formed between two atoms by the sharing of three pairs of electrons is called triple bond.

Question 8:
The electron distribution of nitrogen atom is 2, 5. To attain stability, how many more electrons does nitrogen need?
Solution:
In order to attain the stability, nitrogen atom will require three more electrons.

Page No.42:

Question 1:
When two nitrogen atoms combine to form N, how will they attain the octet structure? Try to complete the illustration.

Solution:

Question 2:
 If the single bond in F, can be indicated as F – F and the double bond in O, as O : O, how is the triple bond of nitrogen to be indicated?

• Try to write down the bond in a hydrogen molecule in this manner.

Solution:

• The triple bond of nitrogen is indicated as N ≡ N.
• The bond in a hydrogen molecule can be shown as:

Question 3:

• In order to attain the electronic structure of helium and thus become stable, how many electrons are required?
• Electron distribution of chlorine is 2, 8, 7. How can this attain stability?

Solution:

• One electron is required to attain the electronic structure of helium and become stable..
• Chlorine needs one electron to complete its octet.

Question 4:
      Look at the chemical bonding between hydrogen and chlorine.

• How many pairs of electrons are shared?
• Is this covalent bond a single bond or a double bond?
• How is the bond indicated?
  See how the chemical equation for this reaction is written.
  H₂ + Cl₂ → HCl

• Examine whether this is a balanced equation. If not, balance it.

Solution:

• One pair of electrons is shared between the hydrogen and chlorine atom.
• This covalent bond is a single bond.
• This bond is indicated as H-CI
• This is not a balanced equation. The complete balanced. equation is given as,
  H₂ + Cl₂ → 2HCl

Question 5:
Look at how the bonding in carbon tetrachloride (CCl₄) molecule is illustrated.

• How many pairs of electrons shared by the carbon atom with chlorine atom?
  Look at how this bonding is represented in a simplified manner.

• In this molecule, how many covalent bonds does carbon form? What about each chlorine atom?
• Is there any relation between the number of covalent bonds formed by each atom and the valency of that particular atom?
• Valency of carbon – 4
• Number of covalent bonds formed ………………………………..
• Valency of chlorine – 1
• Number of covalent bonds formed ………………………………..
• Is this true in other familiar covalent molecules also?

Solution:

• Four pairs of electrons are shared by the carbon atom with chlorine atom
• In this molecule, carbon atom forms four covalent bonds. Chlorine atom forms one covalent bond.
• Yes. The number of covalent bonds formed and the valency are equal.
• Valency of carbon – 4Number of covalent bonds formed 4.
• Valency of chlorine – 1Number of covalent bonds formed 1.
• Yes. This is true for other familiar covalent molecules also.

Page No.43:

Question 1:
Methane is a compound formed by the combination of carbon and hydrogen. Chemical formula is CH₄. Draw its molecular structure and trace the bonds.

Solution:

complete its outer most shell (to achieve complete octet) and become stable.
Hydrogen atom has 1 electron and it needs 1 more electron to complete its outer most shell (to achieve duplet state).
Thus, the carbon atom shares its 4 valence electrons with four hydrogen atoms and forms a methane molecule.
Question 2:
How does the difference in chemical bonding affect the properties of compounds? Common salt is an ionic compound. Wax is a covalent compound. Compare their properties. See the differences.
Solution:
Common salt is an ionic compound. But wax is a covalent compound.
Common salt has a definite crystal shape. But wax has no definite shape. These two are found in solid state. Molten and aqueous solution of common salt conducts electricity. But a solution of wax is non-conducting.
Question 3:
Given below is a table showing the properties of certain substances.

Substance	Electrical Conductivity			Melting point °C	Boiling point °C
	Solid state	Molten State	Dissolved state (in water)
A	Yes	Yes	Does not dissolve	1540	2760
B	No	No	Does not dissolve	65	120
C	No	Yes	Yes	808	1465

Analyse the data given in the table and try to find out the following.

• The substance likely to be an ionic compound.
• The substance that is likely to be a metallic element.
• The substance likely to be a covalent compound.

Solution:

• A. It shows electrical conductivity in solid state and molten state. However, it does not dissolve in water.
• B. There is no electrical conductivity in low melting point, boiling point and in solid state. Also it does not dissolve in water.
• C. It will conduct electricity in high melting point, boiling point, in molten state and in dissolved state.