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Ch.22 - The Main Group Elements
All textbooksMcMurry 8th EditionCh.22 - The Main Group ElementsProblem 22.23b
Chapter 22, Problem 22.23b

The following pictures represent structures of the hydrides of four second-row elements:
(1)
(2)
(3)
(4)
(b) Which compound has the lowest boiling point?

Verified step by step guidance
1
Identify the second-row elements in the periodic table, which are lithium (Li), beryllium (Be), boron (B), carbon (C), nitrogen (N), oxygen (O), and fluorine (F).
Recognize that hydrides are compounds formed between hydrogen and another element. For second-row elements, these hydrides are: LiH, BeH2, BH3, CH4, NH3, H2O, and HF.
Understand that boiling points are influenced by intermolecular forces such as hydrogen bonding, dipole-dipole interactions, and London dispersion forces.
Consider that CH4 (methane) is a nonpolar molecule with only London dispersion forces, which are weaker compared to hydrogen bonding present in NH3, H2O, and HF.
Conclude that CH4, having only weak London dispersion forces and no hydrogen bonding, will have the lowest boiling point among the hydrides of second-row elements.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hydride Structures

Hydrides are compounds formed between hydrogen and other elements. The structure of a hydride can significantly influence its physical properties, including boiling point. For second-row elements, the type of bonding (ionic, covalent, or metallic) and molecular geometry play crucial roles in determining the boiling point of the hydride.
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Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion between molecules. These forces, including hydrogen bonding, dipole-dipole interactions, and London dispersion forces, directly affect boiling points. Compounds with stronger intermolecular forces typically have higher boiling points, while those with weaker forces have lower boiling points.
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Trends in Boiling Points

Boiling points of hydrides generally exhibit trends based on molecular weight and electronegativity of the constituent elements. As you move down a group in the periodic table, boiling points tend to increase due to greater molecular weight and stronger dispersion forces. Conversely, for similar molecular weights, electronegativity differences can lead to variations in boiling points due to the strength of intermolecular forces.
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Related Practice
Textbook Question

In the following pictures of binary hydrides, ivory spheres

represent H atoms or ions, and burgundy spheres represent

atoms or ions of the other element.

(1)

(2)

(3)

(4)

(b) What is the oxidation state of hydrogen in compounds (1), (2), and (3)? What is the oxidation state of the other

element?

Textbook Question

The following models represent the structures of binary hydrides of second-row elements:

b. Draw an electron-dot structure for each hydride. For which hydride is there a problem in drawing the structure? Explain.

Textbook Question

The following pictures represent structures of the hydrides of four second-row elements:

(1)

(2)

(3)

(4)

(a) Which compound has the highest melting point?

Textbook Question

Look at the location of elements A, B, C, and D in the following periodic table:


(b) Classify each oxide as basic, acidic, or amphoteric.

Textbook Question

Look at the location of elements A, B, C, and D in the following periodic table:

(e) Which of these oxides has the highest melting point? Which has the lowest melting point?

Textbook Question

Consider the six second- and third-row elements in groups 4A–6A of the periodic table:


Possible structures for the binary fluorides of each of these elements in its highest oxidation state are shown below.


(a) Identify the nonfluorine atom in each case, and write the molecular formula of each fluoride.