punjab text book notes 9th chemistry

1. Chapter 8
• The most abundant metal is aluminium
• The most precious metal is platinum
• The most useable metal is iron
• The most reactive metal is cesium
• The most valuable metal is uranium
• The lightest metal is lithium (d = 0.53 g cm
• The heaviest
• The least conductor of heat is lead.
• The best conductor metals are silver and gold
• The most ductile and malleable metals are gold and silver
1. What type of elements are metals?
Ans. Metals are the elements (except hydrogen) which are electropositive and form cations
by losing electrons.
2. Name a metal which exists in liquid form?
Ans. Mercury is a metal which
3. What is the nature of metal oxide?
Ans. Metals oxides are basic in nature
4. Which group of metals is highly reactive?
Ans. Alkali metals are highly reactive
ionization energy values.
Chemical Reactivity
• The most abundant metal is aluminium
• The most precious metal is platinum
• The most useable metal is iron
• The most reactive metal is cesium
• The most valuable metal is uranium
• The lightest metal is lithium (d = 0.53 g cm-3
)
• The heaviest metal is osmium (d = 22.5 g cm-3
)
• The least conductor of heat is lead.
• The best conductor metals are silver and gold
• The most ductile and malleable metals are gold and silver
What type of elements are metals?
Metals are the elements (except hydrogen) which are electropositive and form cations
Name a metal which exists in liquid form?
ercury is a metal which exists in liquid form.
What is the nature of metal oxide?
are basic in nature.
Which group of metals is highly reactive?
highly reactive because they have largest size and the lowest
y values.
Test yourself 8.1
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Chemical Reactivity
ADNAN SOHAIL
Metals are the elements (except hydrogen) which are electropositive and form cations
largest size and the lowest

2. Chapter 8
5. Why sodium metal is more reactive than magnesium metal?
Ans. Sodium metal is mo
 Sodium has bigger atomic size (
 Sodium has low ionization energy
6. Name a metal which can be cut with knife?
Ans. Sodium metal can be cut
7. Name the best ductile and malleable metal?
Ans. The best ductile and malleable metals are gold and silver
8. Name the metal which is the poorest conductor of heat?
Ans. The least conductor of heat is lead.
9. What do you mean by malleable and
Ans.
 A metal which can be hammered into sheets
 A metal which can be drawn into wires

10. Why alkali metals are more reactive than alkaline earth metals?
Ans. Alkali metals are more reactive than alkaline earth metals
 Alkali metals have bigger atomic sizes than
 Alkali metals have
11. What do you mean by metallic character?
Ans. Metals have the tendency to lose their valance electrons. This
termed as electropositivity or metallic character.
12. Why metallic character decreases along a period and increases in a group?
Ans. Along period, when we move left to right, atomic size decreases and ionization energy
increases due to which ability of a metal to lose electron decreases.
From to bottom in a group
ability of a metal to lose electron increases.
1. Give the applications of silver?
Ans.
 Alloys of silver with copper are widely used in making coins, silver
ornaments.
 Compounds of silver are widely used in photographic films and dental preparations.
 Silver also has important applications in mirror industry.
2. Why is silver not used in pure form?
Ans. Being very soft metal silver is not used in pure form. It is mostly used in the form of
alloys with copper.
Chemical Reactivity
Why sodium metal is more reactive than magnesium metal?
is more reactive than magnesium because:
has bigger atomic size (186 pm) than magnesium (160pm
ionization energy (496 kjmol-1
) than magnesium (
Name a metal which can be cut with knife?
metal can be cut with knife.
Name the best ductile and malleable metal?
ductile and malleable metals are gold and silver.
Name the metal which is the poorest conductor of heat?
The least conductor of heat is lead.
What do you mean by malleable and ductile?
can be hammered into sheets is called malleable.
can be drawn into wires is ductile.
Why alkali metals are more reactive than alkaline earth metals?
lkali metals are more reactive than alkaline earth metals because:
have bigger atomic sizes than alkaline earth metals
have low ionization energy than alkaline earth metals
What do you mean by metallic character?
Metals have the tendency to lose their valance electrons. This property of a metal is
termed as electropositivity or metallic character.
Why metallic character decreases along a period and increases in a group?
, when we move left to right, atomic size decreases and ionization energy
which ability of a metal to lose electron decreases.
group, atomic size increases and ionization energy decreases due this
ability of a metal to lose electron increases.
Give the applications of silver?
Alloys of silver with copper are widely used in making coins, silver
Compounds of silver are widely used in photographic films and dental preparations.
Silver also has important applications in mirror industry.
used in pure form?
Being very soft metal silver is not used in pure form. It is mostly used in the form of
Test yourself 8.2
2
Chemical Reactivity
ADNAN SOHAIL
160pm).
than magnesium (738 kJmol-1
).
because:
alkaline earth metals.
alkaline earth metals.
property of a metal is
Why metallic character decreases along a period and increases in a group?
, when we move left to right, atomic size decreases and ionization energy
, atomic size increases and ionization energy decreases due this
Alloys of silver with copper are widely used in making coins, silver-ware and
Compounds of silver are widely used in photographic films and dental preparations.
Being very soft metal silver is not used in pure form. It is mostly used in the form of

3. Chapter 8
3. What do you mean by 24 carat gold?
Ans. Purity of gold is shown by
that is present in 24 parts of alloy. Twenty four
4. Why is gold used to make jewelry?
Ans. Gold is very nonreactive or inert metal. It is not affected by atmosphere. It is not even
affected by any single mineral acid or base.
ornamental metal.
5. Why is platinum used for making jewelry?
Ans. Platinum is used to make jewelry items because of its unique characteristics like
colour, beauty, strength,
diamonds and other gemstones, enhancing their brilliance.
6. What is difference between steel and stainless steel?
Ans.
 An alloy of iron mixed with a small amount of carbon is called
 An alloy of steel with chromium and nickel is called stainless steel.
7. How is platinum used as a catalyst in automobiles and what are advantages of this
use?
Ans. An alloy of platinum, palladium and rhodium is used as catalyst in automobiles as
catalytic converter. It converts most of the toxic gases (CO, NO
into less harmful carbon dioxide, nitrogen and water vapour.
1. Why valency of chlorine is I?
Ans. The valency of chlorine atom is 1, as
2. Which factor controls the non
Ans. The non-metallic character depends upon the electron affinity and electronegativity of
the atom.
3. Why fluorine is more non
Ans. Fluorine is more non
 It is small size and has
 It has high electronegativity
 It has high electron affinity
4. Iodine exists in solid state, can it be beaten
Ans. Iodine is a non-metal.
hammer to form sheets.
5. Can liquids and gases be brittle?
Ans. Liquids and gases can not be brittle. Brittleness is the characteristic only solids.
Chemical Reactivity
What do you mean by 24 carat gold?
Purity of gold is shown by carats. This indicates the number of parts by weight of gold
that is present in 24 parts of alloy. Twenty four (24) carat gold is pure.
Why is gold used to make jewelry?
Gold is very nonreactive or inert metal. It is not affected by atmosphere. It is not even
any single mineral acid or base. Because of its inertness in atmosphere, it is an
Why is platinum used for making jewelry?
Platinum is used to make jewelry items because of its unique characteristics like
colour, beauty, strength, flexibility and resistance to tarnish. It provides a secure setting for
diamonds and other gemstones, enhancing their brilliance.
What is difference between steel and stainless steel?
An alloy of iron mixed with a small amount of carbon is called steel.
An alloy of steel with chromium and nickel is called stainless steel.
How is platinum used as a catalyst in automobiles and what are advantages of this
An alloy of platinum, palladium and rhodium is used as catalyst in automobiles as
catalytic converter. It converts most of the toxic gases (CO, NO2) being emitted by vehicles
into less harmful carbon dioxide, nitrogen and water vapour.
Why valency of chlorine is I?
valency of chlorine atom is 1, as it accepts only 1 electron in its outermost shell.
Which factor controls the non-metallic character of the elements?
metallic character depends upon the electron affinity and electronegativity of
Why fluorine is more non-metallic than chlorine?
luorine is more non-metallic than chlorine because:
It is small size and has high nuclear charge.
It has high electronegativity than chlorine.
high electron affinity than chlorine.
Iodine exists in solid state, can it be beaten with hammer to form sheets?
metal. Non-metals are brittle (break easily) and can
Can liquids and gases be brittle?
Liquids and gases can not be brittle. Brittleness is the characteristic only solids.
Test yourself 8.3
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Chemical Reactivity
ADNAN SOHAIL
the number of parts by weight of gold
Gold is very nonreactive or inert metal. It is not affected by atmosphere. It is not even
Because of its inertness in atmosphere, it is an
Platinum is used to make jewelry items because of its unique characteristics like
flexibility and resistance to tarnish. It provides a secure setting for
steel.
An alloy of steel with chromium and nickel is called stainless steel.
How is platinum used as a catalyst in automobiles and what are advantages of this
An alloy of platinum, palladium and rhodium is used as catalyst in automobiles as
) being emitted by vehicles
it accepts only 1 electron in its outermost shell.
metallic character depends upon the electron affinity and electronegativity of
with hammer to form sheets?
can not be beaten with
Liquids and gases can not be brittle. Brittleness is the characteristic only solids.

4. Chapter 8
6. Why the oxygen is called non
Ans. Non-metals form negative ions (anions) by gaining electrons
2 electrons, therefore, it is a non
7. Name two non-metals which are both brittle and non
Ans. Carbon and Phosphorus are both brittle and non
8. Name the most abundant non
Ans. Oxygen is the most abundant non
9. Give the non-metallic trend in halogens
Ans. As we move from top to bottom in halogen family, electron affinity and
electronegativity decreases. Due to this, non
10. Why do the non-metals accept electrons readily?
Ans. The non-metals accept electrons readily
 They are highly electronegative elements.
 They have high electron affinity values.
 They accept electron
11. Why non-metals do not react with dilute acids while metals do react?
Ans.
 Non-metals do not react with dilute acids because non
acceptors.
 Metals react with acids by transferring
gas and metal salt is formed.
12. How can we distinguish a metal from a non
Ans.
Metals
 Almost all metals are solids
 They are good conductor of heat and
electricity.
 They possess met
 They are hard.
 They have high melting and boiling
points.
 They have high densities.
13. How we can distinguish a substance is metal or non
Ans. Metals react with acid producing H
acids. e.g
Zn
14. Why is HF a weak acid?
Ans. Strong acid is one which ionizes almost completely in its aqueous solution. HF is weak
acid because it’s very small amount dissociates into its ions. The reason of low ionization is
the presence of hydrogen bonding among HF molecules.
Chemical Reactivity
Why the oxygen is called non-metal?
metals form negative ions (anions) by gaining electrons. Oxygen
therefore, it is a non-metal.
metals which are both brittle and non-ductile?
Carbon and Phosphorus are both brittle and non-ductile.
Name the most abundant non-metal in the earth’s crust?
Oxygen is the most abundant non-metal in earth’s crust.
metallic trend in halogens?
As we move from top to bottom in halogen family, electron affinity and
electronegativity decreases. Due to this, non-metallic character also decreases.
metals accept electrons readily?
metals accept electrons readily because:
They are highly electronegative elements.
They have high electron affinity values.
They accept electrons to complete their octet and become stable.
metals do not react with dilute acids while metals do react?
do not react with dilute acids because non-metals are itself electron
react with acids by transferring electron to reduce H+
ion. By this reaction H
gas and metal salt is formed.
How can we distinguish a metal from a non-metal by simple physical methods?
Metals
Almost all metals are solids
They are good conductor of heat and
They possess metallic luster.
have high melting and boiling
They have high densities.
Non-metals
 Non-metals are brittle (break easily).
 Non-metals are bad conductors of
heat and electricity
 They are not shiny.
 They are generally soft.
 They have low melting and boiling
points.
 They have low densities.
How we can distinguish a substance is metal or non-metal with the help of an acid?
acid producing H2 gas and metal salt. Non-metals do not react with
Zn + HCl ZnCl2 + H2
Why is HF a weak acid?
Strong acid is one which ionizes almost completely in its aqueous solution. HF is weak
very small amount dissociates into its ions. The reason of low ionization is
the presence of hydrogen bonding among HF molecules.
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Chemical Reactivity
ADNAN SOHAIL
Oxygen atom can accept
As we move from top to bottom in halogen family, electron affinity and
metallic character also decreases.
to complete their octet and become stable.
metals do not react with dilute acids while metals do react?
metals are itself electron
ion. By this reaction H2
metal by simple physical methods?
metals
are brittle (break easily).
metals are bad conductors of
nd electricity.
They are not shiny.
They are generally soft.
low melting and boiling
They have low densities.
metal with the help of an acid?
metals do not react with
Strong acid is one which ionizes almost completely in its aqueous solution. HF is weak
very small amount dissociates into its ions. The reason of low ionization is

5. Chapter 8 Chemical Reactivity
ADNAN SOHAIL
SHORT ANSWER QUESTIONS
1. Why reactivity of metals increases down the group?
Ans. As we move down the group atomic size of metals increases. The ability of an atom to
lose electron increases. Therefore, reactivity of metals increases down the group.
2. State the physical properties of metals?
Ans.
 Almost all metals are solids (except mercury).
 They have high melting and boiling points, (except alkali metals).
 They possess metallic luster and can be polished.
 They are malleable (can be hammered into sheets), ductile (can be drawn into wires)
and give off a tone when hit.
 They are good conductor of heat and electricity.
 They have high densities.
 They are hard (except sodium and potassium).
3. Why nitrogen forms compounds with alkaline earth metals directly?
Ans. Alkaline earth metals being electropositive elements lose their valence electrons
readily. Nitrogen being most electronegative elements accepts these electrons. The
compounds of nitrogen with alkaline earth metals are called nitrides.
4. Why the second ionization energy of magnesium is higher than the first one?
Ans. The first ionization energy of magnesium is low but the second ionization energy of
magnesium is very high. It becomes very difficult to remove second electron from the Mg+
ion as nuclear charge attracts the remaining electrons strongly. As a result of this attraction,
size of the ion decreases.
5. How oxygen reacts with group II A metals?
Ans. Group II A metals are less reactive towards oxygen and oxides are formed on heating.
6. What is relationship between electropositivity and ionization energy?
Ans. Electropositive character of an element depends upon its ionization energy. The
elements having low ionization energy are more electropositive.
7. Why electropositivity decreases from left to right in a period?
Ans. From left to right in a period, atomic size decreases due to the increase of nuclear
charge. Outer most electrons are strongly bound with nucleus. Due to this, ionization energy
increases and electropositivity decreases.
8. How electropositivity depends upon size and nuclear charge of an atom?
Ans Electropositive character depends upon the ionization energy which in turn depends
upon size and nuclear charge of the atom. Small sized atoms with high nuclear charge have
high ionization energy value. In this way, atoms having high ionization energy are less
electropositive or metallic.
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6. Chapter 8 Chemical Reactivity
ADNAN SOHAIL
Rana Academy M.Phil chemistry
9. Why ionization energies of alkaline earth metals are higher than alkali metals?
Ans. Electropositive character depends upon the ionization energy which in turn depends
upon size and nuclear charge of the atom. Small sized atoms with high nuclear charge have
high ionization energy value. In this way, atoms having high ionization energy are less
electropositive or metallic. That is the reason alkali metals have the largest size and the
lowest ionization energy in their respective periods. Therefore, they have the highest metallic
character.
10. Why silver and gold are least reactive?
Ans. Reactivity of a metal depends upon its tendency to lose electrons. Since silver and gold
do not lose their valence electrons easily, therefore they are least reactive.
11. Can pure gold be used for making ornaments? If not why?
Ans. Pure gold can not be used for making ornaments. Gold is too soft to be used as such.
It is always alloyed with copper, silver or some other metal.
12. Why copper is used for making electrical wires?
Ans. Copper is an excellent conductor of heat and electricity. It is also highly ductile (can be
drawn into wires) and malleable metal.
13. What is the trend of variation in densities of alkali metals?
Ans. When we move from top to bottom in a group, the increase of nuclear mass of alkali
metals is greater than increase in their atomic sizes. Thus, the densities of alkali metals
increase from top to bottom in a group.
14. Which metal is used for metal work?
Ans. Copper is used for metal work because it is easily workable. It is resistant to corrosion.
15. Why magnesium is harder than sodium?
Ans. Metal hardness depends upon strength of metallic bond. Magnesium is harder than
sodium because metallic bond in it is stronger than that of sodium.
16. Why calcium is more electropositive than magnesium?
Ans. Electropositive character of metals depends upon atomic size and ionization energy.
Calcium has large size and low ionization energy than magnesium. This is the reason that
calcium is more electropositive than magnesium.
17. Why ionization energy of Na is less than Mg?
Ans. Sodium and Magnesium belong to same period. Magnesium is present next to sodium
in same period (3rd
period). Due to strong nuclear charge Magnesium has smaller atomic
size and high ionization energy than sodium.
18. Why the ionization energy of Na is more than K?
Ans. The elements having small atomic size and high nuclear charge have high ionization
energy. Since, Na atom has small size and high nuclear charge, as compared to K. That is
why, ionization energy of sodiun (Na) is more than potasium (K).
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