Hydrogen bonds are intermolecular forces between hydrogens and adjacent molecules. These adjacent molecules must contain either fluorine, oxygen, or nitrogen, the three most electronegative atoms. These electronegative atoms pull electrons away from the bonded hydrogen, giving it a small positive charge and giving themselves a slightly negative charge. When the positive hydrogen of one molecule come close to a negative charge on another, the opposite charges attract and pull the molecules close together to form a hydrogen bond. The hydrogen must be bonded to oxygen (-OH), fluorine (HF), or nitrogen (-NH) to have this charging effect.

Hydrogen bonding takes place when a hydrogen atom is attracted to a highly electronegative atom in another molecule. Hydrogen bonding takes place between hydrogen and either nitrogen, oxygen, or fluorine. Carbon has an electronegativity similar to hydrogen's, and will not hydrogen bond with hydrogens in other molecules.

Only molecules with -OH, -FH, or -NH groups can form hydrogen bonds.

Ethene is an organic molecule composed of two carbon atoms, joined by a double bond, and four hydrogen atoms.

Ethene, like all molecules, exhibits London dispersion forces. This molecule, however, has no net dipole moment, so it will not exhibit dipole-dipole attraction. Also, even though it contains hydrogens, it does not exhibit hydrogen bonding. To exhibit hydrogen bonding, the hydrogen atoms must be attached to more electronegative atoms, namely nitrogen, fluorine, or oxygen. Finally, ionic bonding is only present in ionic compounds, not organic compounds.

Intermolecular forces are transient forces between two separate molecules. Water is a polar molecule. The oxygen atom carries a slight positive charge, while the hydrogen atoms carry slight negative charges. This is the result of the large difference in electronegativity between oxygen and hydrogen. When two water molecules are next to each other, the partially positive hydrogen will be attracted to the partially negative oxygen. This attraction is known as a hydrogen bond.

Ionic bonds, covalent bonds, and double bonds are all intramolecular forces. These are stable bonds between atoms that establish the identity of the molecule. Breaking any of these bonds would alter the identity of the compound.

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. 

An element cannot be broken down into other substances. Compounds consist of two or more elements and thus can be broken down. Matter is simply anything that takes up space and has mass; both elements and compounds are matter. Subatomic particles are the building blocks of atoms. Though atoms are the units that make up elements and are the smallest units to have the properties of an element, subatomic particles themselves do not display characteristic of an element.

Isotopes are the same element that have the same number of protons and electrons.  The difference is in their atomic weight because they have different numbers of neutrons.