Rank these compounds in order of increasing boiling

1.Rank these compounds in order of increasing boiling

point:

(a) fluorine, F2;

(b) hydrogen fluoride, HF;

Rank these compounds in order of increasing symmetry:

(a) CH4,

(b) NH3,

Rank these compounds in order of increasing boiling point:

(a) CH4,

(b) NH3,

How do the electron-dot structures of elements in the same group in the periodic table compare with one another?
How many more electrons can fit within the valence shell of a fluorine atom?
How many more electrons can fit within the valence shell of a hydrogen atom?
How is the number of unpaired valence electrons in an atom related to the number of bonds that the atom can form? 8. What happens when hydrogen’s electron gets close to the

valence shell of a fluorine atom?

The Correct Answer and Explanation is :

Answers and Explanation

1. Ranking Compounds by Boiling Point (Increasing Order)

Boiling point is influenced by intermolecular forces (London dispersion, dipole-dipole, and hydrogen bonding).

Ranking:
Fluorine (F₂) < Hydrogen chloride (HCl) < Hydrogen fluoride (HF)

Fluorine (F₂) has weak London dispersion forces, leading to a very low boiling point (~−188°C).
Hydrogen chloride (HCl) exhibits dipole-dipole interactions, increasing its boiling point (~−85°C).
Hydrogen fluoride (HF) has hydrogen bonding, the strongest intermolecular force, leading to the highest boiling point (~19.5°C).

2. Ranking Compounds by Symmetry (Increasing Order)

Molecular symmetry is influenced by shape and bond angles.

Ranking:
H₂O < NH₃ < CH₄

Water (H₂O) has a bent shape due to two lone pairs, making it the least symmetrical.
Ammonia (NH₃) has a trigonal pyramidal shape with one lone pair, giving it intermediate symmetry.
Methane (CH₄) is tetrahedral, the most symmetrical structure.

3. Ranking Compounds by Boiling Point (Increasing Order)

CH₄ < NH₃ < H₂O

Methane (CH₄) has weak London dispersion forces, leading to a very low boiling point (~−161°C).
Ammonia (NH₃) exhibits hydrogen bonding, but only one hydrogen bond per molecule (~−33°C).
Water (H₂O) has extensive hydrogen bonding, leading to the highest boiling point (~100°C).

4. Electron-Dot Structures in the Same Group

Elements in the same group have the same number of valence electrons, which determines their chemical behavior. For example, all Group 17 (halogens) have 7 valence electrons, forming similar electron-dot structures.

5. Additional Electrons in Fluorine’s Valence Shell

Fluorine has 7 valence electrons and can hold 8 in total. Thus, it can accommodate 1 more electron to complete its octet.

6. Additional Electrons in Hydrogen’s Valence Shell

Hydrogen has 1 valence electron and follows the duet rule (maximum of 2 electrons). It can hold 1 more electron to be stable.

7. Unpaired Valence Electrons and Bonding

The number of unpaired valence electrons determines an atom’s bonding capacity:

Carbon (C) has 4 unpaired electrons → forms 4 bonds
Nitrogen (N) has 3 unpaired electrons → forms 3 bonds
Oxygen (O) has 2 unpaired electrons → forms 2 bonds

This principle helps predict molecular structures.

8. Interaction of Hydrogen’s Electron with Fluorine

When hydrogen’s electron approaches fluorine, a covalent bond forms. Fluorine’s high electronegativity attracts hydrogen’s electron, completing its octet. This results in hydrogen fluoride (HF), where hydrogen achieves stability by sharing its electron.

Detailed Explanation (300 Words)

Boiling points of substances are determined by intermolecular forces. Fluorine (F₂) has weak London dispersion forces and the lowest boiling point. Hydrogen chloride (HCl) has stronger dipole-dipole interactions due to its polarity. Hydrogen fluoride (HF) exhibits hydrogen bonding, the strongest force, giving it the highest boiling point.

Symmetry depends on molecular shape. Water (H₂O) is bent due to lone pairs, making it the least symmetrical. Ammonia (NH₃) is trigonal pyramidal with one lone pair. Methane (CH₄) is tetrahedral, making it the most symmetrical.

Boiling points of CH₄, NH₃, and H₂O follow the same intermolecular force pattern: CH₄ (London dispersion) has the lowest, NH₃ (hydrogen bonding) is intermediate, and H₂O (strong hydrogen bonding) is the highest.

Elements in the same periodic group have the same valence electron configuration, affecting their reactivity. Fluorine, for instance, has 7 valence electrons and needs 1 more for stability. Hydrogen, following the duet rule, can hold only one more electron.

The number of unpaired valence electrons dictates how many bonds an atom can form. Carbon has four, allowing it to form four covalent bonds, while oxygen forms two.

When hydrogen’s electron nears fluorine, a highly polar bond forms, as fluorine strongly attracts electrons. This results in HF, where fluorine’s electronegativity causes a partial negative charge, while hydrogen becomes partially positive. This explains HF’s high boiling point and strong intermolecular forces.