Chapter 2, Problem 87QAP

Interpretation Introduction

(a)

Interpretation:

From the given set of elements, the two metals need to be determined.

Concept introduction:

Metals are elements with high electropositive nature. The atoms of element that can donate electron in the presence of an electron deficient species are known as metals. The most electropositive elements belong to the first and second group of the periodic table.

Answer to Problem 87QAP

Potassium and strontium are metals.

Explanation of Solution

Potassium and strontium are metals.

• Potassium is present in group 1 known as alkali metal group in the periodic table with atomic number of 19. The melting point of potassium is low. It can donate its 1 electron in the valence shell to form +1 charge. It has properties of good conductor of electricity and heat; therefore, it is classified as metal.
• Strontium is present in group 2 (IIA) called as alkaline earth metals with atomic number of 38. It is found in three allotropic crystalline forms. It reacts with water very quickly. It can easily form the thin layer of oxide when it is exposed in air. It can donate its 2 electrons from the valence shell to get +2 charge.

Interpretation Introduction

(b)

Interpretation:

From the given set of elements, the four non-metals need to be determined.

Concept introduction:

Non-metals are elements that are electronegative in nature. They can accept electrons due to their electron deficient nature to from negative charge ions. The elements in group 15 to 18 in the periodic table are considered as non-metals. Here, group 15 is nitrogen family. All the elements that belong to this family can gain 3 electrons to from -3 charge ions. Group 16 and group 17 is oxygen and halogen family respectively. Group 16 elements can gain 2 electrons and group 17 elements can gain 1 electron to complete their octets.

Answer to Problem 87QAP

Oxygen, fluorine, argon and sulfur are non-metals.

Explanation of Solution

Oxygen, fluorine, argon and sulfur are nonmetals.

• Oxygen is present in group 16^th known as oxygen family in the periodic table with atomic number of 8. It is from chalcogen group and it is not a good conductor of electricity and heat. It gains 2 electrons to from ${\text{O}}^{2-}$ ion.
• Fluorine is present in group 17^th known as the halogens with atomic number of 9. It is electronegative in nature and it has five electrons in its 2p orbital, thus, it requires 1 more electron to complete its octet.
• Argon is present in group 18^th known as the noble gases with atomic number of 18. It has a maximum number of valence electrons in its outermost shell. Thus, it is quite stable and does not react with other species.
• Sulfur is present in group 16^th group of the periodic table that is oxygen family. It is also called as the chalcogen with atomic number of 16 and it is not a good conductor of electricity and heat. It requires 2 electrons to complete its octet and from ion with -2 charge.

Interpretation Introduction

(c)

Interpretation:

From the given set of elements, the three elements solid at room temperature need to be determined.

Concept introduction:

The Vander Waal’s force or the intermolecular force between the atoms of molecule determines its state at room temperature. Vander Waal’s forces are of two types, that is, London dispersion forces and strong dipole-dipole forces.

Answer to Problem 87QAP

Sulfur, potassium and strontium are solid at room temperature.

Explanation of Solution

Sulfur, potassium and strontium are solid at room temperature.

Sulfur is present in group 16^th called as the chalcogen or the oxygen family with atomic number of 16. The size of sulfur is very large, therefore, it can only form $p\pi -p\pi$

• bond in the form of lateral overlap and because of this reason, it is found in octatomic molecule (S₈ ). And because of octatomic structure, the Vander Waal’s forces in sulfur are very high which results in the closed packing of molecules. Therefore, it is solid at room temperature.
• Potassium is present in group 1^st known as alkali group in the periodic table with atomic number 19. The metallic bonding of potassium is very strong within the metal cations and the delocalized electrons. Therefore, it requires a large amount of energy to break the metallic bond, so that it is solid at room temperature.
• Strontium is present in group 2 (IIA) in the periodic table known as alkaline earth metals with atomic number of 38. The metallic bonds formed by potassium atoms are very strong. Therefore, it requires a large amount of energy to break the metallic bond, and potassium is solid at room temperature.

Interpretation Introduction

(d)

Interpretation:

From the given set of elements, the element found as ${\text{X}}_{\text{8}}$ in nature needs to be determined.

Concept introduction:

Sulphurisan element with atomic symbol S and atomic number 16 belongs to 16th group in the periodic table or oxygen family. It can accept two electron/s to form -2 charge on it.

Answer to Problem 87QAP

Sulfur is found in nature as X₈ or S₈.

Explanation of Solution

Sulfur is present in group 16^th known as the chalcogen or the oxygen family with atomic number of 16. The size of sulfur is very large therefore it can only form $p\pi -p\pi$ bond in the form of lateral overlap, because of this reason it is found in octatomic molecule (S₈ ). As a result of the Octatomic structure, the Vander Waal’s forces in sulfur are very high which results in the closed packing of molecules therefore, it is solid at room temperature.

Interpretation Introduction

(e)

Interpretation:

From the given set of elements, the element that can form a molecular compound need to be determined.

Concept introduction:

Molecular compounds are formed between a non-metal and a non-metal by sharing of electrons. This is because they have similar electronegativity values.

Answer to Problem 87QAP

Oxygen and sulfur from a molecular compound.

Explanation of Solution

Oxygen and sulfur from a molecular compound. Both elements are of same group from periodic table.

• Oxygen is present in group sixteen called as oxygen family of periodic table with atomic number of 8. Oxygen is found as diatomic molecule and it formed s-s bond by axial overlap and pp-pp bond by lateral overlap of p orbitals. Because of this, bond formation the Vander Waals force of attraction is very less in the oxygen, therefore, it is found in gas form at the room temperature.
• Sulfur is present in group 16^th called as the chalcogen or the oxygen family with atomic number of 16. It is a polyatomic molecule and it looks like a soft yellow solid with faint odor. The size of Sulphuratom is very large therefore it can only form pi-pi bond in the form of lateral overlap. As a result of this, it is found in octatomic molecule which is allotrope of sulfur (S₈ ). Because of theoctatomic structure, the Vander Waals force in sulfur is very high which results in the closed packing of molecules.
The S and O can share electrons to from molecular compounds. This is due to the fact that they have approximately same electronegativity values.

Interpretation Introduction

(f)

Interpretation:

From the set of elements, the pair of elements that can form an ionic compound AX needs to be determined.

Concept introduction:

An ionic compound is formed by the combination of ions with opposite charge. Here, the positive charge species is cation and negative charge is anion. The cations and anions are combined in the ratio such as the overall charge on the ionic compound will be zero.

Answer to Problem 87QAP

Potassium and fluorine an ionic compound with the formula KF.

Explanation of Solution

Potassium and fluorine an ionic compound with the formula KF.

• Potassium is present in group one called as alkali group in the periodic table with atomic number of 19. The melting point of potassium is low. It has properties of good conductor of electricity and heat, and it is classified as metal. It can donate its 1 electron to form ${\text{K}}^{+}$ ion.
• Fluorine is present in group 17th called as the halogens with atomic number of 9. It is most chemically active non-metal. It can accept 1 electron to from ${\text{F}}^{-}$ ion.

Thus, ${\text{K}}^{+}$ and ${\text{F}}^{-}$ ions can combine in 1:1 ratio to from KF.

Interpretation Introduction

(g)

Interpretation:

From the set of elements, the pair of elements that can form an ionic compound AX₂ needs to be determined.

Concept introduction:

An ionic compound is formed by the combination of ions with opposite charge. Here, the positive charge species is cation and negative charge is anion. The cations and anions are combined in the ratio such as the overall charge on the ionic compound will be zero.

Answer to Problem 87QAP

Strontium and fluorine form an ionic compound with the formula SrF₂.

Explanation of Solution

Strontium and fluorine form an ionic compound with the formula SrF₂.

• Fluorine is present in group 17 called as the halogens with atomic number of 9. It is the most chemically active non-metal. It can accept 1 electron to from ${\text{F}}^{-}$ ion.
• Strontium is present in group 2 (IIA) called as alkaline earth metals with atomic number of 38. It can donate its 2 electrons to from ${\text{Sr}}^{2+}$ ion.

Thus, ${\text{Sr}}^{2+}$ ion and ${\text{F}}^{-}$ ion can combine in 1:2 ratio to from SrF₂.

Interpretation Introduction

(h)

Interpretation:

From the set of elements, the pair of elements that can form an ionic compound A₂ X needs to be determined.

Concept introduction:

An ionic compound is formed by the combination of ions with opposite charge. Here, the positive charge species is cation and negative charge is anion. The cations and anions are combined in the ratio such as the overall charge on the ionic compound will be zero.

Answer to Problem 87QAP

Potassium and sulfur form an ionic compound with the formula K₂ S.

Explanation of Solution

Potassium and sulfur form an ionic compound with the formula K₂ S.

• Potassium is present in group one called as alkali group in the periodic table with atomic number of 19. The melting point of potassium is low. It has properties of good conductor of electricity and heat, and it is classified as metal. It can donate its 1 electron to form ${\text{K}}^{+}$ ion.
• Sulfur is present in group 16 called as the chalcogen or the oxygen family with atomic number of 16. It can donate 2 electrons to form ${\text{S}}^{2-}$ ion.

Thus, ionic compound, K₂ S is formed between ${\text{K}}^{+}$ and ${\text{S}}^{2-}$ ions when they combine in 2:1 ratio.

Interpretation Introduction

(i)

Interpretation:

From the set of elements, the element that cannot form any compound needs to be determined.

Concept introduction:

In the periodic table, the elements present in 18^th group are noble gases. They have to complete octets and thus, do not react with other elements in the periodic table.

Answer to Problem 87QAP

Argon.

Explanation of Solution

From the given set, argon is a noble gas with atomic number 18. It belongs to the 18^th group and has complete octet. Due to complete octet, it does not react with other elements in the periodic table.

Interpretation Introduction

(j)

Interpretation:

From the given set of elements, the three elements which are gases at room temperature needs to be determined.

Concept introduction:

Metals are elements with high electropositive nature. The atoms of element that can donate electron in the presence of an electron deficient species are known as metals. The most electropositive elements belong to the first and second group of the periodic table. Most of the metals are solid at room temperature, only mercury is liquid at room temperature.

Non-metals are elements that are electronegative in nature. They can accept electrons due to their electron deficient nature to from negative charge ions. The elements in group 15 to 18 in the periodic table are considered as non-metals. Here, group 15 is nitrogen family, and all the elements belonging to this family can gain 3 electrons to from -3 charge ions. Group 16 and group 17 is oxygen and halogen family respectively. Group 16 elements can gain 2 electrons and group 17 elements can gain 1 electron to complete their octets. Most of the non-metals are gases at room temperature only bromine is liquid at room temperature.

Answer to Problem 87QAP

Oxygen, fluorine and argon are gases at room temperature.

Explanation of Solution

Oxygen, fluorine and argon are gases at room temperature.

• Oxygen is present in group 16^thcalled as oxygen family of periodic table with atomic number of 8.
• Fluorine is present in group 17^th called as the halogens with atomic number of 9.
• Argon is present in group 18^thcalled as the noble gases with atomic number of 18.

All the above elements are non-metals thus, gases at room temperature.