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7.4. Comparison of Hydrides of Group 15 and 16
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Today, we will discuss the hydrides of Group 15, starting with ammonia (NH₃) and phosphine (PH₃). Can anyone tell me the bond angle in NH₃?
Is it 107°?
Correct! And what about PH₃?
I think it's 94°.
That's right! Now, why do these bond angles differ? It’s due to the lone pairs and the differences in atomic sizes. Let's discuss the basicity next. Which hydride is the most basic?
I believe it's NH₃.
Indeed! Ammonia is a strong base, followed by phosphine. Remember, basicity decreases from NH₃ to PH₃ and then to the water and hydrosulfide mentioned later. Would anyone like to explain why this occurs?
It could be because NH₃ has hydrogen bonding while PH₃ doesn’t.
Exactly! Hydrogen bonding in NH₃ leads to stronger intermolecular forces, thus making it a stronger base. Let’s summarize: NH₃ has a bond angle of 107° and is the strongest base among these hydrides.
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Now, let's look at the hydrides of Group 16, namely H₂O and H₂S. Who can tell me the bond angles for these?
H₂O is 104.5° and H₂S is 92.1°.
Correct! H₂O is known for its strong hydrogen bonding, which is absent in H₂S. How does this affect their boiling points?
H₂O has a higher boiling point than H₂S because of hydrogen bonding.
That's right! Water is a liquid at room temperature, while hydrogen sulfide is a gas. Now, can someone explain the acidic nature of these two hydrides?
Water is amphoteric, acting as both an acid and base, while H₂S is a weak acid.
Good point! We also noted that as we move down the group, the acid strength of the hydrides increases. To wrap up, the trend we see is H₂O being highly polar and hydrogen-bonded compared to H₂S.
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Create a free accountToday we are going to compare the hydrides from both groups. What are the key similarities and differences we've discussed?
Both groups have hydrides that decrease in stability down the group.
The bond angles differ quite a bit between groups, too.
Exactly! Group 15 has a valency of 3 or 5, whereas Group 16 has valency 2 or 4. How about we touch briefly on acidic nature?
Hydrides like NH₃ are less acidic compared to H₂O.
Great observation! And remember that hydrogen bonds in NH₃ and H₂O enhance their physical properties unlike PH₃ and H₂S. Summarizing, we've looked at basicity, bond angles, hydrogen bonding, and stability. Excellent work today!
Overview
Short Summary
This section discusses the hydrides of Group 15 and 16 elements, comparing their properties such as bond angles, basicity, and hydrogen bonding.
Medium Summary
In this section, we explore the hydrides formed by elements from Groups 15 and 16 of the periodic table. Key aspects include how properties like bond angles, basicity, and hydrogen bonding differ between hydrides such as ammonia (NH₃), phosphine (PH₃), water (H₂O), and hydrogen sulfide (H₂S). The trends in these properties across the groups are also highlighted.
Detailed Summary
Comparison of Hydrides of Group 15 and 16
This section delves into the hydrides of Group 15 (Nitrogen Family) and Group 16 (Oxygen Family) elements, focusing on their unique properties and how they compare to each other.
Key Properties of Hydrides:
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Bond Angles: The bond angles of the hydrides vary significantly:
- NH₃ (Ammonia): 107°
- PH₃ (Phosphine): 94°
- H₂O (Water): 104.5°
- H₂S (Hydrogen Sulfide): 92.1°
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Basicity: The basicity of these hydrides decreases in the order:
- NH₃ > PH₃ > H₂O > H₂S
- NH₃ is a strong base, while H₂S is a weak acid.
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Hydrogen Bonding: Hydrogen bonding is present in NH₃ and H₂O but not in PH₃ or H₂S. This phenomenon increases the boiling points of NH₃ and H₂O significantly compared to their counterparts.
Trends Across the Two Groups:
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Valency:
- Group 15: Forms hydrides with a valency of 3 or 5.
- Group 16: Forms hydrides with a valency of 2 or 4.
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Common Oxidation States:
- Group 15: +3, +5, -3.
- Group 16: +4, +6, -2.
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Hydride Stability:
- For both groups, stability of hydrides tends to decrease down the group.
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Catenation Ability:
- Group 15 shows catenation in phosphorus, while Group 16, particularly sulfur, has a stronger capability to catenate.
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Acidic Nature of Oxides:
- Higher in Group 15, particularly for nitrogen, while lower in Group 16 as you go from oxygen to polonium.
This section is significant as it highlights not just the distinct characteristics of the hydrides but also their broader implications in chemistry, such as acidity, basicity, and bonding theories that govern the behavior of these elements.
Key Concepts
Core takeaways and short definitions to help you quickly recall the key ideas from this section.
Hydride Stability: Stability of hydrides decreases down the group in both Group 15 and Group 16.
Basicity Trend: Basicity decreases from NH₃ > PH₃ > H₂O > H₂S.
Bond Angles: Differences in bond angles are observed among the hydrides of different groups.
Hydrogen Bonding: Present in NH₃ and H₂O, absent in PH₃ and H₂S.
Examples
Step-by-step examples to apply the section's ideas and test your understanding.
Ammonia (NH₃) exhibits strong hydrogen bonding resulting in a higher boiling point compared to phosphine (PH₃).
Water (H₂O) is amphoteric, showing both acidic and basic properties, unlike hydrogen sulfide (H₂S), which behaves primarily as a weak acid.
Memory Aids
Interactive tools to help you remember key concepts
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Glossary
Hydride
A compound formed between hydrogen and another element, typically a non-metal.
Basicity
The ability of a substance to accept protons or donate electron pairs.
Catenation
The ability of an element to form chains of atoms with itself.
Hydrogen Bonding
A type of dipole-dipole interaction that occurs between molecules when a hydrogen atom is covalently bonded to a highly electronegative atom.