9th chemistry chapter 8 solved exercise short questions

Chemical Reactivity

9th chemistry chapter 8 solved exercise short questions

Solved Exercise Short Questions

Q#1 : Why reactivity of metals increases down group ?

Reactivity of metals increases down the group .

Reason :

Because down the group ,

  • Size of atoms increases
  • Number of shells increases
  • electropositive character or metallic character increases

Due to these reasons , it becomes easier to lose its valence electrons.

Q#2 : State the physical properties of metals .

  1. Almost all metals are solids (except mercury).
  2. Metals have high melting and boiling points (except alkali metals).
  3. Metals possess metallic luster and can be polished.
  4. Metals are malleable, ductile and give off a tone when hit.
  5. Metals are good conductor of heat and electricity.

Q#3 : Why nitrogen forms compound with alkaline earth metals directly ?

Nitrogen forms compounds with alkaline earth metals directly.

Reason :

Because alkaline earth metals are very powerful reductants and are easily oxidized. While dinitrogen with a triple bond , is very stable .The dinitrogen bond can be reduced .

Alkaline earth metals form stable metallic nitrides when heated with nitrogen.

3 Mg + N2 → Mg3N2

Q#4 : Why the second ionization energy of magnesium is higher than the first one ?

Magnesium has higher second ionization energy.

Reason :

After removal of 1st electron from magnesium atom , the remaining electrons are 11 and number of protons are 12 .

This results in increase in nuclear charge or force over valence electrons.

It is difficult to remove 2nd electron from magnesium uni-positive ion.

Hence , magnesium has higher second ionization energy.

Q#5 : How oxygen reacts with group 2 metals ?

Reaction with oxygen :

They are less reactive towards oxygen and oxides are formed on heating .

2 Mg + O2 → 2 MgO

Q#6 : What is relationship between electro-positivity and ionization energy ?

  • Electro-positivity depends upon the ionization energy which in turn depends upon size and nuclear charge of an atom , So
  • Small sized atoms with high nuclear charge have high ionization energy.

Q#7 : Why electro-positivity decreases from left to right in a period?

Electro-positivity decreases across the period from left to right . It means elements in the start of a period are more metallic .

→This is because of two reasons ;

  • Size of atoms decreases
  • Nuclear charges increases

Q#8 : How electro-positivity depends upon size and nuclear charge of an atom ?

When the size of atoms increases , electro-positivity increases and it becomes easier to lose electrons .

If nuclear charge increases the electro-positivity decreases and it becomes difficult to remove the electrons from outermost shell.

Q#9 :Why ionization energies of alkaline earth metals are higher than alkali metals ?

Alkaline earth metals have higher ionization energies than alkali metals .

Reason :

Because metals of alkaline earth are :

  • smaller
  • have more nuclear charge

That is why ; they are reactive but less than alkali metals .

Q#10 : Why are silver and gold least reactive ?

Silver and gold are least reactive because :

Reason :

  • These metals do not lose their electrons easily.
  • They do not have the tendency to make cations.
Playlist of 9th class Physics , solved exercise
Playlist of 9th class Chemistry , solved exercise , free notes

Q#11 : Can pure gold be used for making ornaments ? If not why ?

No , pure gold cannot be used for making ornamentals .

Reason :

Gold is too soft to be used as such , it is always alloyed with copper , silver or some other metals.

Q#12 : Why is copper used for making electrical wires ?

Copper is used for making electrical wires .

Reason :

Because copper is very good conductor of electricity.

Q#13 : What is the trend of variation in densities of alkali metals ?

Densities of alkali metals increases down the group in a periodic table except potassium which has less density than sodium .

Q#14 : Which metal is used for metal work ?

The metals are used in fire work due to their characteristic flame colors when they ignite in air .

  • Na” gives golden yellow color.
  • Ca” gives red color etc.

Q#15 : Why is magnesium harder than sodium ?

Magnesium is harder than sodium .

Reasons :

Because ;

  • In magnesium , Metallic bonding is stronger
  • The atomic size of magnesium is less than sodium

That’s why the atoms of magnesium are packed closer to each other to give it rigidity .

Q#16 : Why is calcium more electro-positive than magnesium ?

Calcium is more electro-positive than magnesium

Reason :

Metallic character or electropositive character increases down the group due to increase in size of atoms .

  • Due to large size of atoms , valence electrons are loosely held and can be easily withdrawn from their shells.

Q#17 : Why is ionization energy of Na less than Mg ?

Ionization energy of Na is less than Mg

Reason :

Because Na requires less energy to lose its valence electron than Mg due to its ;

  • Larger atomic size &
  • Less nuclear charge

Q#18 : Why the ionization energy of Na is more K ?

Ionization energy of Na is more than K

Reason :

Down the group;

  • Electro-positive character increases
  • Ionization energy decreases

It becomes easier to release their electrons down the group.

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