Hydrogen bonding occurs between a hydrogen atom on one molecule and a very electronegative atom—namely oxygen, nitrogen, or fluorine—on a neighboring molecule. This electrostatic force results in a stronger intermolecular bond than would otherwise be present without the hydrogen bond. A stronger intermolecular bond results in a higher boiling point.

Water (H₂O) exhibits hydrogen bonding between the hydrogen of one water molecule and the oxygen of another water molecule. Since sulfur is not as electronegative as oxygen, hydrogen sulfide (H₂S) does not exhibit hydrogen bonding. This is the reason why water is a liquid at room temperature, while hydrogen sulfide is a gas.

Wrong answers explained: Neither water nor hydrogen sulfide has ionic bonds. Both have covalent bonds and London dispersion force, but this does not explain why water's boiling point is higher. Heisenberg bonding does not exist and is a misleading answer option.

When hydrogen is bound to either fluorine, oxygen, or nitrogen, the hydrogen atom carries little of the electron density of the covalent bond. This partially positively charged hydrogen atom may interact with the partial negative charge located on adjacent electronegative atoms such as F, N, or O on adjacent molecules. Note that hydrogen bonds are intermolecular forces, not intramolecular. This means that hydrogen bonds form between two separate molecules. They plan an important role in the chemistry of water, and other compounds that exhibit hydrogen bonding. 

Resonance is the movement of electrons from one bond to another. This helps to shift the electron distribution between multiple atoms, creating molecular stability. In order for resonance to occur, there must be a pi bond next to a sigma bond. A pi bond is a double bond or triple bond and a sigma bond is a single bond. During resonance, the electrons from the pi bond move around causing the double (or triple) bond to shift positions. This frequently occurs with oxygen and nitrogen because they have several valence electrons and can readily form pi bonds, but these elements are not required to form resonance structures.

Resonance structures are a way of describing the different possible locations of delocalized electrons within a molecule. Although a molecule might have several correct resonance forms, often, one is more stable than the others. Molecules whose structures differ in the locations of atoms are called isomers. 

Solubility of solid and liquid solutes in aqueous solutions can be increased by raising the temperature of the solution. Raising the temperature increases the amount of kinetic energy of the water molecules, allowing them to better interact with the solute particles and prevent the formation of a solid lattice.

Adding other solutes with similar properties will generally decrease solubility by the common ion effect, or else will not affect solubility at all. Increasing pressure will help increase the solubility of a gas in solution, but will not affect solutions that only contain solids and liquids. Note that gas solubility will also increase with decreased temperature. This is opposite to the relationship between temperature and the solubility of solids. Low temperature will reduce the kinetic energy of gases, making them more similar to liquids, while lowering the temperature of a solid will further lower its kinetic energy and decrease its similarities with a liquid solvent.

It is possible to reduce the solubility by adding a salt that increases the concentration of an ion that is created by the insoluble salt. This is called the common ion effect.

Silver chloride will dissociate into silver and chlorine ions in solution.

If sodium chloride is added to the solution, the concentration of chlorine ions increases.

This will push the equilibrium of the silver chloride dissociation to the left, thus decreasing the solubility of silver chloride.

There are some general solubility guidelines that can help you predict which salts are soluble.

1. All compounds containing ammonium, nitrate, or alkali metals are soluble.

2. Compounds with halogens as the anion are soluble. The three noted exceptions are when they are bonded to silver, mercury, or lead.

3. Sulfate compounds are soluble, except when bonded to mercury, lead, or the heavier alkaline earth metals.

 is an example of an insoluble sulfate compound because the sulfate is attached to barium, a heavy alkaline earth metal.

Solubility of solids increases when temperature increases because the increased kinetic energy increases the chance that a solute molecule gets surrounded by solvent molecules. Solubility for gases decreases when temperature increases because the increased kinetic energy allows for the gas molecules to break the intermolecular forces holding them in the solution, letting them bubble out of the solvent.

If given the solubility product constant for a salt, we can determine the solubility for the salt as well. In order to do this, we need to use an ICE table and the equilibrium constant expression.

Initial: When the salt is added to water, there are no ions initially in solution. Because the salt is a solid, its concentration is irrelevant.

Change: When one molecule of barium fluoride dissolves, one barium ion and two fluoride ions are introduced to the solution. As a result, barium ions increase by , and fluoride ions increase by .

End: The equilibrium expression for this salt is , which will allow us to calculate the solubility based on the change in ion concentration.

The solubility for barium fluoride is .

Definition of :

for .

For :

Due to the chemical formula, there will be twice as many chloride ions as lead ions.

Solve for the unknown variable:

Multiply times the given volume:

Multiply times the molar mass of :