The diethyl ether molecule contains an oxygen atom that is not bonded to a hydrogen atom, making it a hydrogen bond acceptor. A hydrogen attached to carbon can also participate in hydrogen bonding when the carbon atom is bound to electronegative atoms, as is the case in chloroform CHCl 3. As in a molecule where a hydrogen is attached to nitrogen, oxygen, or fluorine, the electronegative atom attracts the electron cloud from around the hydrogen nucleus and, by decentralizing the cloud, leaves the hydrogen atom with a positive partial charge.
Hydrogen bonds occur in inorganic molecules, such as water, and organic molecules, such as DNA and proteins. In biology, intramolecular hydrogen bonding is partly responsible for the secondary, tertiary, and quaternary structures of proteins and nucleic acids. The hydrogen bonds help the proteins and nucleic acids form and maintain specific shapes.
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:. Skip to main content. Liquids and Solids. A European Space Agency astronaut Pedro Duque of Spain watches a water bubble float between him and the camera, showing his image refracted, on the International Space Station. B A large water sphere made on a 5 cm diameter wire loop by U. Weird Science. Adhesion is similar to cohesion, but it involves unlike i.
Water is very adhesive ; it sticks well to a variety of different substances. Water sticks to other things for the same reason it sticks to itself — because it is polar so it is attracted to substances that have charges. Water adheres to many things— it sticks to plants, it sticks to dishes, and it sticks to your eyebrows when you sweat.
In each of these cases water adheres to or wets something because of adhesion. This is why your hair stays wet after you shower. Molecules of water are actually sticking to your hair Fig. Adhesion also explains why soil is able to hold water and form mud. Investigate the cohesive and adhesive properties of water. The cohesion of water creates surface tension where air and water meet.
You observed this in Activity 2 when you looked at the ability of water to pile on top of a penny without spilling over see Fig. The hydrogen bonds between water molecules at the surface are analogous to the to members of a red rover team holding hands. When playing red rover, team members line up to form a chain to try and prevent someone from running through their joined hands Fig.
The linked hands represent the hydrogen bonds between water molecules that can prevent an object from breaking through. Of course, a faster or heavier person can more easily break through the hand bonds during a game of red rover. Where air and liquids meet there are unbalanced forces. Water molecules very near the surface are being pulled down and to the side by the strong cohesion of water to itself and the strong adhesion of water to the surface it is touching.
The result is a net force of attraction between water molecules a very flat, thin sheet of molecules at the surface see Fig. Because of hydrogen bonding, water can actually support objects that are more dense than it is.
Water molecules stick to one another on the surface, which prevents the objects resting on the surface from sinking. It is also what allowed you to float a paper clip on water and the reason why a belly flop off the high dive into a pool of water is painful.
In Activity 2, you tried to stick two rulers together using a thin film of water between the rulers. Water acted like glue, and you were able to use one ruler to lift the other ruler using the adhesiveness of water see Fig. An alcohol is an organic molecule containing an -OH group. Any molecule which has a hydrogen atom attached directly to an oxygen or a nitrogen is capable of hydrogen bonding.
Hydrogen bonds also occur when hydrogen is bonded to fluorine, but the HF group does not appear in other molecules.
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. This phenomenon can be used to analyze boiling point of different molecules, defined as the temperate at which a phase change from liquid to gas occurs.
They have the same number of electrons, and a similar length. The van der Waals attractions both dispersion forces and dipole-dipole attractions in each will be similar. However, ethanol has a hydrogen atom attached directly to an oxygen; here the oxygen still has two lone pairs like a water molecule.
Hydrogen bonding can occur between ethanol molecules, although not as effectively as in water. Except in some rather unusual cases, the hydrogen atom has to be attached directly to the very electronegative element for hydrogen bonding to occur. The boiling points of ethanol and methoxymethane show the dramatic effect that the hydrogen bonding has on the stickiness of the ethanol molecules:.
It is important to realize that hydrogen bonding exists in addition to van der Waals attractions. For example, all the following molecules contain the same number of electrons, and the first two have similar chain lengths. The higher boiling point of the butanol is due to the additional hydrogen bonding.
Comparing the two alcohols containing -OH groups , both boiling points are high because of the additional hydrogen bonding; however, the values are not the same. The boiling point of the 2-methylpropanol isn't as high as the butanol because the branching in the molecule makes the van der Waals attractions less effective than in the longer butanol.
Hydrogen bonding also occurs in organic molecules containing N-H groups; recall the hydrogen bonds that occur with ammonia. The two strands of the famous double helix in DNA are held together by hydrogen bonds between hydrogen atoms attached to nitrogen on one strand, and lone pairs on another nitrogen or an oxygen on the other one.
In order for a hydrogen bond to occur there must be both a hydrogen donor and an acceptor present. The donor in a hydrogen bond is usually a strongly electronegative atom such as N, O, or F that is covalently bonded to a hydrogen bond. The hydrogen acceptor is an electronegative atom of a neighboring molecule or ion that contains a lone pair that participates in the hydrogen bond.
Since the hydrogen donor N, O, or F is strongly electronegative, it pulls the covalently bonded electron pair closer to its nucleus, and away from the hydrogen atom. The hydrogen atom is then left with a partial positive charge, creating a dipole-dipole attraction between the hydrogen atom bonded to the donor and the lone electron pair of the acceptor. This results in a hydrogen bond. Although hydrogen bonds are well-known as a type of IMF, these bonds can also occur within a single molecule, between two identical molecules, or between two dissimilar molecules.
Intramolecular hydrogen bonds are those which occur within one single molecule. This occurs when two functional groups of a molecule can form hydrogen bonds with each other. In order for this to happen, both a hydrogen donor a hydrogen acceptor must be present within one molecule, and they must be within close proximity of each other in the molecule. For example, intramolecular hydrogen bonding occurs in ethylene glycol C 2 H 4 OH 2 between its two hydroxyl groups due to the molecular geometry.
Intermolecular hydrogen bonds occur between separate molecules in a substance. They can occur between any number of like or unlike molecules as long as hydrogen donors and acceptors are present in positions where they can interact with one another.
When we consider the boiling points of molecules, we usually expect molecules with larger molar masses to have higher normal boiling points than molecules with smaller molar masses. This, without taking hydrogen bonds into account, is due to greater dispersion forces see Interactions Between Nonpolar Molecules. Larger molecules have more space for electron distribution and thus more possibilities for an instantaneous dipole moment. However, when we consider the table below, we see that this is not always the case.
We see that H 2 O, HF, and NH 3 each have higher boiling points than the same compound formed between hydrogen and the next element moving down its respective group, indicating that the former have greater intermolecular forces. The same effect that is seen on boiling point as a result of hydrogen bonding can also be observed in the viscosity of certain substances.
Substances capable of forming hydrogen bonds tend to have a higher viscosity than those that do not for hydrogen bonds. Generally, substances that have the possibility for multiple hydrogen bonds exhibit even higher viscosities. Hydrogen bonding cannot occur without significant electronegativity differences between hydrogen and the atom it is bonded to.
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