Chemistry Chapter 15: Allotropy & Oxidation States

Questions and Answers

Which element shows a maximum oxidation state of +5?

Nitrogen

Arsenic

Bismuth

Phosphorus (correct)

What happens to the tendency to exhibit a -3 oxidation state as you go down the group?

It stabilizes at a constant level

It increases significantly

It decreases (correct)

It becomes the most common oxidation state

Which oxidation state of nitrogen does not form compounds with halogens?

+5 (correct)

Which of the following elements is rarely found in the -3 oxidation state?

Bismuth Signup and view all the answers

Among the following, which element has a significant inert pair effect leading to stability in +3 oxidation state?

Bismuth Signup and view all the answers

Which statement accurately describes nitrogen compared to other group elements?

It has a smaller size and higher ionisation enthalpy. Signup and view all the answers

Which compound is a well-characterized +5 oxidation state compound of bismuth?

BiF5 Signup and view all the answers

In what context does nitrogen exhibit disproportionation reactions?

In acid solutions Signup and view all the answers

Which hydride has the highest melting point among the listed Group 15 hydrides?

NH3 Signup and view all the answers

What is the E–H distance for AsH3?

151.9 pm Signup and view all the answers

Which statement about the oxides formed by Group 15 elements is true?

Arsenic and antimony oxides are amphoteric. Signup and view all the answers

Which of the following statements is correct regarding the stability of trihalides?

Trihalides of nitrogen are not stable except NF3. Signup and view all the answers

What is the trend in acidic character of the oxides down the Group 15 elements?

It decreases down the group. Signup and view all the answers

What is the boiling point of SbH3?

254.6 K Signup and view all the answers

How does the covalent character of pentahalides compare to trihalides?

Pentahalides are more covalent than trihalides. Signup and view all the answers

Which compound is an example of a binary compound formed by a Group 15 element and a metal?

Ca3N2 Signup and view all the answers

Which halide is the most stable among F, Cl, Br, and I?

F Signup and view all the answers

What is the structure of hexafluorides?

Octahedral Signup and view all the answers

Which of the following fluorides is in a liquid state?

SeF4 Signup and view all the answers

What type of hybridization is found in the structure of dichlorides and dibromides?

sp Signup and view all the answers

What is the geometry of SF4?

See-saw Signup and view all the answers

What is the reason for H2S being less acidic than H2Te?

Dissociation enthalpy decreases down the group Signup and view all the answers

Which of the following is NOT an example of a dimeric halide?

SnCl2 Signup and view all the answers

What is a common method for obtaining dioxygen in the laboratory?

Heating oxygen-containing salts Signup and view all the answers

What is the structure of PCl5 at room temperature?

Trigonal bipyramidal Signup and view all the answers

Which of the following oxoacids of phosphorus has a phosphorus oxidation state of +4?

Hypophosphoric acid Signup and view all the answers

Which statement correctly describes the P-Cl bonds in PCl5?

The axial bonds are longer than the equatorial bonds. Signup and view all the answers

What is the balanced equation for the reaction of PCl5 with water?

PCl5 + H2O → H3PO4 + HCl Signup and view all the answers

What is a characteristic of orthophosphoric acid?

It contains three P-OH bonds. Signup and view all the answers

Which oxoacid of phosphorus requires red phosphorus and alkali for its preparation?

Hypophosphoric acid Signup and view all the answers

What is the oxidation state of phosphorus in orthophosphorous acid?

+3 Signup and view all the answers

Which of the following statements about the bonds in hypophosphorous acid is true?

It has one P-H bond. Signup and view all the answers

How does the atomic number affect the melting and boiling points of Group 16 elements?

Melting and boiling points increase with increasing atomic number. Signup and view all the answers

What is the primary reason for the difference in oxidation states observed in sulfur compared to oxygen?

Sulfur's larger size allows it to accommodate more oxidation states. Signup and view all the answers

What is the trend in the stability of the -2 oxidation state as one moves down Group 16?

Stability of -2 oxidation state decreases. Signup and view all the answers

Which factor contributes to the anomalous behavior of oxygen compared to other Group 16 elements?

Oxygen's small size and high electronegativity. Signup and view all the answers

What type of bonding is observed in the +4 and +6 oxidation states of sulfur, selenium, and tellurium?

Primarily covalent bonding. Signup and view all the answers

Why does oxygen rarely exceed a covalency of four in bonds?

It lacks available d orbitals. Signup and view all the answers

Which of the following accurately describes the properties of hydrides formed by Group 16 elements?

The melting and boiling points of hydrides decrease down the group. Signup and view all the answers

In the context of Group 16 elements, what is the main consequence of the inert pair effect?

Increased stability of the +4 oxidation state. Signup and view all the answers

Study Notes

Allotropy and Oxidation States

All elements except nitrogen exhibit allotropy.
Common oxidation states for Group 15 elements: -3, +3, and +5.
Down the group, tendency for -3 oxidation state decreases due to increased size and metallic character; bismuth rarely forms -3 state compounds.
Stability of +5 oxidation state decreases down the group, with BiF5 being the only well-characterized Bi(V) compound.
Nitrogen shows multiple oxidation states: +1, +2, +4, with a maximum covalency of 4 due to limited orbitals.
The heavier Group 15 elements can utilize vacant d-orbitals, allowing for expanded covalency.

Anomalous Properties of Nitrogen

Nitrogen's distinct properties stem from its small size, high electronegativity, and absence of d-orbitals.
Disproportionation occurs in nitrogen’s oxidation states +1 to +4 in acidic solutions, such as the reaction of HNO2 to give HNO3 and NO.
Phosphorus exhibits similar disproportionation behavior across its oxidation states, forming +5 and -3 states in intermediates.

Hydrides of Group 15

Hydrides' properties vary significantly, for instance, NH3 has a higher melting point (195.2 K) compared to BiH3 which is not well-defined.
General trend shows higher boiling points and bond distances as atomic number increases; NH3 is the most stable.
Bond angles decrease down the group, with NH3 at 107.8° and BiH3 significantly lower at 91°.

Reactivity Patterns

Group 15 elements form two types of oxides: E2O3 and E2O5, with acidic character decreasing down the group.
Oxides of nitrogen and phosphorus are purely acidic, while those of bismuth are predominantly basic.
Reactions with halogens produce trihalides (EX3) and pentahalides (EX5). Notably, nitrogen cannot form pentahalides due to lack of d-orbitals; only NF3 is stable among nitrogen trihalides.
Trihalides are generally covalent, except for BiF3.

Oxoacids of Phosphorus

Phosphorus forms several oxoacids, characterized by distinct oxidation states ranging from +1 to +5, with varying bond types including P−OH, P=O, and P−P.
Key oxoacids include hypophosphorous acid (H3PO2), orthophosphorous acid (H3PO3), and orthophosphoric acid (H3PO4).

Trends in Group 16 Elements

Group 16 elements show oxidation states of -2, +2, +4, and +6, with stability of -2 oxidation state diminishing down the group.
Oxygen, being highly electronegative, typically exists in a -2 state except in OF2, where it exhibits +2.
Anomalous properties of oxygen include strong hydrogen bonding in H2O due to its small size and high electronegativity, unlike H2S.

Reactivity with Hydrogen and Halogens

Group 16 elements produce hydrides (H2E) with stability decreasing down the group.
Halides are more stable than fluorides, and hexafluorides exhibit octahedral structures.
Dihalides formed by sp hybridization showcase tetrahedral structures and include dimeric forms that can undergo disproportionation.

Dioxygen Preparation

Laboratory methods for obtaining dioxygen include heating oxygen-rich salts (e.g., KClO3) and thermal decomposition of metal oxides.

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Description

Explore the fascinating concepts of allotropy and oxidation states in elements of Group 15, including the unique properties of nitrogen. Delve into how bonding and stability change as you move down the group, with a focus on the oxidation states exhibited by these elements.