The s-Block Elements

Question 1

grw the ionic radii of alkali metal ions are smaller than atomic radii of the corresponding atoms

Answer 1

• Alkali metals possess only one electron in their valence shell and during the formation of cation, this electron is lost.
• The cation formed has one electron shell less than the parent atom.
• The removal of the electron increases the effective nuclear charge experienced by the remaining electrons which are pulled closer to the nucleus, resulting in a further decrease in the size.
• combined effect of decrease in electron shells and increase in effective nuclear charge.

Question 2

grw the atomic and ionic radii of alkali metals are the largest in their respective periods

Answer 2

• while moving left to right across a period, the number of shells remains the same but the nuclear charge increases.
• thus the electrons in the valence shell experience a greater pull towards the nucleus.
• this results in a successive decrease in the atomic and ionic radii across a period and alkali metals are the largest in their periods.

Question 3

grw the atomic and ionic radii of alkali metals increase down the group

Answer 3

• as one moves down the group, a new electron shell is added to each element and the nuclear charge increases with increase in atomic number
• increase in the number of shells increases screening effect of inner electrons on the valence electrons and the electron cloud tends to expand since the effective nuclear charge on the valence shell electrons is less
• increase in screening effect dominates over increase in nuclear charge so the atomic and ionic radii of alkali metals increase down the group.

Question 4

grw alkali metals possess very low values of I.P.
or
grw alkali metals have the lowest I.P.

Answer 4

-The akali metals possess electronic configuration of ns1 type
-The noble gas core shields the s-electron from the nucleus and it is held loosely by the nucleus.
- it can be removed easily by applying a small amount of energy

Question 5

grw ionisation energies of alkali metals decrease progressively in gowing from Li to Cs

Answer 5

-as we go down the group the number of shells increase
-due to increased number of shells the screening effect of inner electrons increases
-the size of the atom is bigger
- the valence electrons are more loosely held by the nucleus due to this
-small amount of energy is required to remove the valence electron

Question 6

grw lithium is the strongest reducing agent even though it has the highest value of ionisation energy

Answer 6

• among alkali metals Li+ undergoes hydration to the maximum extent since it is the smallest alkali metal
• the large amount of energy released during hydration compensates the energy needed to remove electron from the Li atom
• this facilitates the release of electron malikng Li the strongest reducing agent among the alkali metals

Question 7

uses of NaCl

Answer 7

1. Sodium chloride is an essential constituent of our food.
2. It is used in freezing mixture.
3. It is used in the purification of soap.

Question 8

Name of process for manufacture of sodium carbonate

Answer 8

Solvay’s process

Question 9

Uses of sodium carbonate/washing soda

Answer 9

1. Used for washing purposes in laundry
2. Used for softening hard water
3. Used as a reagent in the laboratory
4. Used in paper, textile, and paint industries

Question 10

How is NaOH prepared?

Answer 10

NaOH is prepared by electrolysis in Castner-Kellner cell

Question 11

What is the electronic configuration of alkaline earth metals?

Answer 11

Alkaline earth metals have ns2 type configuration

Question 12

grw the ionisation energies of alkaline earth metals are low, but higher than those of the corresponding alkali metals

Answer 12

• alkaline earth metals are comparitively larger than all other elements in their period except the alkali metals.
• due to this, they have a large atomic radius and less effective nuclear charge on the valence electrons so their ionisation energies are low
• however, alkali metals being larger, with less nuclear charge than alkaline earth metals, have a lower ionisation energy than alkaline earth metals.

Question 13

grw the ionisation energies of alkaline earth metals decrease on moving down the group

Answer 13

-as we go down the group the number of shells increase
-due to increased number of shells the screening effect of inner electrons increases
-the size of the atom is bigger
- the valence electrons are more loosely held by the nucleus due to this
-small amount of energy is required to remove the valence electron

Question 14

grw the second ionisation energy values of alkaline earth metals are much smaller than those of alkali metals

Answer 14

• the unipositive cation of an alkaline earth metal has ns1 type configuration
• the unipositive cation of an alkali metal has the electronic configuration of the nearest gas which is extremely stable
• thus, a large amount of energy is required to remove another electron from the unipositive cation of an alkali metal
• less amount of energy is required to remove an electron from a cation with ns1 configuration since it is less stable

Question 15

Uses of slaked lime/calcium hydroxide

Answer 15

1. Used for softening of hard water
2. Used as a laboratory reagent for detection of carbon dioxide
3. Used as a building material for making mortar and plaster

Question 16

Gypsum- chemical formula

Answer 16

CaSO4 . 2H2O

Question 17

Gypsum- uses

Answer 17

1. Used in the manufacture of plaster of paris
2. Used in the manufacture of cement and mortar
3. It is also used for the treatment of soil