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 .
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 .
- Almost all metals are solids (except mercury).
- Metals have high melting and boiling points (except alkali metals).
- Metals possess metallic luster and can be polished.
- Metals are malleable, ductile and give off a tone when hit.
- 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.
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.
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 .
Because metals of alkaline earth are :
- 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 :
- These metals do not lose their electrons easily.
- They do not have the tendency to make cations.
Q#11 : Can pure gold be used for making ornaments ? If not why ?
No , pure gold cannot be used for making ornamentals .
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 .
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 .
- 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
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
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
→Down the group;
- Electro-positive character increases
- Ionization energy decreases
It becomes easier to release their electrons down the group.
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