KPK Board 12th class Chemistry Ch 13 S and P Block Elements short questions answers

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Explain reaction of magnesium with H2O?
Reaction with steam magnesium burns in steam with white flame and form white Mg and H2 gas.

Mg + H2O à MgO + H2

Why the NaCl does not conduct electricity in solid state?
Sodium chloride does not conduct electricity in solid state because ions are fixed at their position.
Rubidium is below potassium in Group I-A predicts how it will react with.
(a) Water

(b) Chlorine and describe the product.

As we go down the group IA the reactivity of elements increases due to increases in their metallic character. So rubidium can react vigorously with water and chlorine.



Why halogens are so reactive?
Halogens are very reactive in nature their reactivity decreases down the group. The reactivity of halogens is attributed to low dissociation energy of halogens molecules. Fluorine is the most reactive halogen due to low energy of F-F bond, high oxidizing power and high electroSnegativity. The decrease in reactivity of halogen from F2 and I2 is clear from their reaction with H2 to from hydrogen halide. F2 to do so while explode in the dark Cl2 also does the same Br2 only react with H2 in the presence of catalyst at 200C while I2reaction is reversible.
What is flame test?
Flame test is a qualitative test and is used to detect the presence of certain elements is metals ions in the given sample. Each metals and gives its own characteristic color to the flame.
Write down any four characteristics of group II-A elements.
  1. Atomic radius of this group increases down the group.
  2. Ionization energy of 2nd a group decreases down the group.
  3. Electronegativity also decreases down the group.
  4. These group elements have high melting and boiling point.
Explain the thermal stability of nitrates and carbonates of group II-A elements.
The thermal stability of the nitrates and carbonates of group II-A elements increases down the group. The increase in the stability of carbonates down the groups is indicated by the temperature to which decompose. This is due to the decreasing in the polarizing power of cations down the group. This decrease in polarizing power of cations is due to increasing the size of cation and decreasing charge density down the group.
Why carbonates of group I-A elements are more thermally stable than those of group II-A.
Carbonates of group IA are thermally more stable than the carbonates of group IIA. It is because due to large size, lesser charge density group IA elements have lesser polarization power as compare to group II A element which has smaller size and more polarization power due to which they can easily polarize the carbonate anion and release CO2 easily. While on the other hand group IA elements do not have enough polarizing power distort the carbonate anion and release CO2 thus their carbonates are much more stable than carbonates of group IIA elements upon heating.
Why Beryllium is differs from the members of it group?
Beryllium is different from the member of its own family due to its small size and high charge density.
Explain the structure and stability of chlorides of group IV-A elements.
All these elements give tetrachloride MCl4. Tetrachloride are covalent in nature that occur due to SP3 hybridization. Some of group IV elements can form dichloride MCl2 the chlorides like SnCl2 to PbCl2 are ionic in nature.
Why fluorine is stronger oxidizing agent than chlorine?
Fluorine is stronger oxidizing agent than other halogens due to its low bond and enthalpy, small size and high value of reduction potential.

Why BeCl2 is covalent and not ionic?
BeCl2 is a covalent compound due to small size of Be +2 cation and high charge density. According to Fajan‘s Rule small size and high charge density of cation results in covalent bonding.

So BeCl2 is covalent in nature.

Explain the amphoteric nature of Be (OH)2 .
Be(OH)2 amphoteric in nature it can react both acid and bases.

Basic:  Be(OH)2 +HClàBeCl2+H2o

Acidic:  Be(OH)2+2NaOHàNa2[Be(OH)4]

Why the atomic radius of argon than all the member of third period?
The argon belongs to noble gases or zero group is larger than all the element and it has greater radius then other element in the 3rd row of the periodic table because it is not atomic radii it is a Vander Waal radius, which is half distance between two closest non-bonded atoms. It is always greater then atomic radius because it does not form any chemical bond.
Why fall in ionization energy occurs at aluminum and Sulphur in same period?
Both Al and S show unexpected decrease in their ionization energies in the 3rd row elements.

Aluminum:  Aluminum has lower ionization energy because in Aluminum the last electron is in 3pix which is higher energy orbital, which means it is farther from nucleus. So it can easily be removed, which result decrease in ionization energy of Aluminum.

Sulphur: Sulphur also has unexpected lower ionization energy because of the presence of an extra electron in p orbital i.e. it is ns2 np4 system and extra electron is present in 3px orbital which result in electron-electron repulsion. So electron could be removed easily that result decrease in ionization energy sulphur.

Why the compounds of Su4+ are covalent in nature while those of Sn2+ are ionic?
Sn+4 from covalent compound while Sn+2 from ionic compound because according to Fajan’s rule large charge on cation from covalent compound, which result decrease in size on Sn+2 will from covalent compound due to its smaller size and more charge.
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