Use chemical principles to discuss the following observations: CO2 sublimes at -78^∘ C, whereas

Use chemical principles to discuss the following...

Use chemical principles to discuss the following observations: $\mathrm{CO}_{2}$ sublimes at $-78^{\circ} \mathrm{C},$ whereas $\mathrm{SiO}_{2}$ boils at $2200^{\circ} \mathrm{C}$. HF boils at $19^{\circ} \mathrm{C}$, whereas $\mathrm{HCl}$ boils at $-85^{\circ} \mathrm{C}$. $\mathrm{CF}_{4}$ boils at $-128^{\circ} \mathrm{C},$ whereas $\mathrm{SiF}_{4}$ boils at $-86^{\circ} \mathrm{C}$.

Use chemical principles to discuss the following observations:
$\mathrm{CO}_{2}$ sublimes at $-78^{\circ} \mathrm{C},$ whereas $\mathrm{SiO}_{2}$ boils at $2200^{\circ} \mathrm{C}$. HF boils at $19^{\circ} \mathrm{C}$, whereas $\mathrm{HCl}$ boils at $-85^{\circ} \mathrm{C}$. $\mathrm{CF}_{4}$ boils at $-128^{\circ} \mathrm{C},$ whereas $\mathrm{SiF}_{4}$ boils at $-86^{\circ} \mathrm{C}$.

Key Concepts

London Dispersion Forces

London dispersion forces are weak, temporary attractions caused by fluctuations in electron density in molecules. They are the predominant intermolecular forces in non-polar molecules and generally increase with greater molecular size and polarizability. Variations in these forces can explain differences in boiling points between molecules like CF? and SiF?, where differences in molecular mass and electron cloud polarizability lead to variations in the strength of these dispersion forces.

Network Covalent Bonding

Network covalent bonding involves a continuous network of covalent bonds extending throughout the material, leading to very high melting and boiling points. Materials such as SiO?, which exhibit network covalent bonding, have much higher boiling points because a large amount of energy is needed to break the extensive covalent bonds, in contrast to molecular substances like CO? that are held together by much weaker intermolecular forces.

Molecular Structure and Geometry

The three-dimensional arrangement of atoms in a molecule affects its overall polarity and the types of intermolecular forces it can engage in. Molecular structure and symmetry determine whether a molecule will have a permanent dipole moment and whether it can form specific interactions like hydrogen bonds. This is critical when comparing substances such as HF and HCl, or CF? and SiF?, where structural differences influence their boiling points and other physical properties.

Intermolecular Forces

Intermolecular forces play a crucial role in determining the phase change temperatures of substances. They include various types of attractions such as hydrogen bonding, dipole-dipole interactions, and London dispersion forces. The magnitude and nature of these forces explain why some compounds have much higher boiling points compared to others, as stronger interactions require more energy to overcome when transitioning from liquid to gas phases.

Hydrogen Bonding

Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is directly bonded to a highly electronegative atom such as fluorine, oxygen, or nitrogen. This interaction can significantly elevate boiling points, as seen when comparing compounds like HF to HCl, where the presence of hydrogen bonding in HF leads to a higher boiling point despite having comparable molecular sizes.

Transcript

00:01 Okay, so this question asks us to use some chemical principles to explain some observations.

00:08 The first one is the co2 sublime at minus 78 .0 .c.

00:23 Well, for the silicon dioxide, it actually bores at 2 ,200 degrees c.

00:33 So we say the silicon oxide has a much higher boiling point than the carbon dioxide, much, much higher.

00:42 Why? they are actually in the same group, right, carbon and silica.

00:47 The molecular mass is the difference between the molecular mass between them are not that different.

00:56 Why? because for carbon dioxide, it's molecular solids.

01:01 And for the same silica oxide, it's actually a, we know it's actually a covariant solid.

01:17 Calmer dioxide forms molecules, why silica dioxide is not molecules.

01:23 They're actually linked together.

01:26 So, which means in the silicon oxide, the boiling point are determined by the strength of the covalent bond.

01:37 The bond between the silicon and oxide.

01:40 However, the interactions between the boiling point and carbon dioxide are related to the interactions between the molecules inside the carbon dioxide.

01:54 So definitely covalent bonding is much more stronger force than the molecular interactions, which is when the words interaction.

02:05 So because the interaction is the interaction much stronger.

02:09 For the covalent solid, it has much higher boiling point or melting point...

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