The boiling point of a liquid is the temperature at which its vapor pressure is equal to the pressure of the gas above it. The normal boiling point of a liquid is the temperature at which its vapor pressure is equal to one atmosphere (760 torr).

Different liquids have different boiling points depending on the strength of bonding between the particles and the mass of the particles. The heavier the particles in the liquid, and the stronger the bonding, the higher the boiling point will be.

The boiling point of a liquid varies according to the applied pressure; the normal boiling point is the temperature at which the vapour pressure is equal to the standard sea-level atmospheric pressure (760 mm [29.92 inches] of mercury). At sea level, water boils at 100° C (212° F).

The pressure of gas above a liquid affects the boiling point. In an open system this is called atmospheric pressure. The greater the pressure, the more energy required for liquids to boil, and the higher the boiling point.

Factors affecting melting point – definition

• Ionic Bonds.
• Intermolecular Forces.
• Shape of Molecules.
• Size of Molecule.

The similarity between melting points and boiling points means that the same factors that impact the melting point of a compound will also impact the boiling point. Therefore, the strength and types of intermolecular forces that are found within the liquid compound will affect the boiling point.

Branching decreases the boiling point As the length of carbon chain increases, the surface area of the compound will also increase. Van der Waals dispersion force is proportional to the surface area. Branching in molecules decreases the surface area thereby decreasing the attractive force between individual molecules.

As the pressure applied to the liquid surface is increased, the energy needed for the liquid molecules to expand to gas phase also increases. Hence, a higher temperature is required to change liquid to gas phase. So, boiling point of liquid rises on increasing pressure.

Tungsten

helium, at the top of group 0, has the lowest boiling point of any element.

Zn has no unpaired electron hence it has lowest melting and boiling point.

Boiling point

• H hydrogen (H2) use. 20.271 K. −252.879 °C. −423.182 °F. WebEl. 20.28 K.
• He helium. use. 4.222 K. −268.928 °C. −452.07 °F. WebEl. 4.22 K.
• Li lithium….

1330 °C. 2426 °F. WebEl. 1615 K.

Of all metals in pure form, tungsten has the highest melting point (3,422 °C, 6,192 °F), lowest vapor pressure (at temperatures above 1,650 °C, 3,000 °F), and the highest tensile strength.

The boiling point increases with increased pressure up to the critical point, where the gas and liquid properties become identical. The boiling point cannot be increased beyond the critical point. Likewise, the boiling point decreases with decreasing pressure until the triple point is reached.

Intermolecular forces (IMFs) can be used to predict relative boiling points. The stronger the IMFs, the lower the vapor pressure of the substance and the higher the boiling point.

Alkynes have higher boiling points than alkanes or alkenes, because the electric field of an alkyne, with its increased number of weakly held π electrons, is more easily distorted, producing stronger attractive forces between molecules.

In order from strongest to weakest, the intermolecular forces given in the answer choices are: ion-dipole, hydrogen bonding, dipole-dipole, and Van der Waals forces.

The polar substance always has the higher boiling point, indicating greater attractive forces between separate molecules, that is, larger intermolecular forces. Table 8.3. 1 Boiling Points of Otherwise Similar Polar and Nonpolar Substances.

In general, larger molecules have higher boiling points than smaller molecules of the same kind, indicating that dispersion forces increase with mass, number of electrons, number of atoms or some combination thereof.

Molecules with hydrogen bonds will always have higher boiling points than similarly sized molecules which don’t have an an -O-H or an -N-H group. The hydrogen bonding makes the molecules “stickier,” such that more heat (energy) is required to separate them.

Polar molecules differ from nonpolar molecules by having positive and negative ends and stronger intermolecular forces of attraction. It takes more energy to separate the molecules from each other, so polar substances have relatively high melting points and boiling points.

A molecule has polar bonds if there is a significant difference in electronegativity between the two elements. If the electronegativities of both elements are very similar or the same, the bonds are non-polar. If this is the case, the entire molecule is also non-polar.

A polar molecule is a molecule in which one end of the molecule is slightly positive, while the other end is slightly negative. A diatomic molecule that consists of a polar covalent bond, such as HF, is a polar molecule.

Non-polar molecules have the lowest melting and boiling points, because they are held together by the weak van der Waals forces. If you need to compare the boiling points of two metals, the metal with the larger atomic radius will have weaker bonding, due to the lower concentration of charge.

Polarity plays a pivotal role in solubility. A polar solute will dissolve in a polar solvent whereas a non-polar solvent will dissolve in a non-polar solvent. If we put a polar solute in a non-polar solvent, it will not dissolve.

Molecular solids generally have low melting points and boiling points due to relatively weak intermolecular attractions that hold the molecules in their solid form.

The more-polar molecules will stick together more and will probably evaporate more slowly than less polar molecules. Less-polar molecules should evaporate faster because they are not as attracted to each other.

Properties of Liquids

• Capillary Action.
• Cohesive and Adhesive Forces.
• Contact Angles.
• Surface Tension.
• Unusual Properties of Water.
• Vapor Pressure.
• Viscosity Viscosity is another type of bulk property defined as a liquid’s resistance to flow.
• Wetting Agents.

Acetone is a polar molecule because it has a polar bond, and the molecular structure does not cause the dipole to be canceled.

Viscosity is governed by the strength of intermolecular forces and especially by the shapes of the molecules of a liquid. Liquids whose molecules are polar or can form hydrogen bonds are usually more viscous than similar nonpolar substances.