A phase is a certain kind of issue that has a specific collection of physical properties. That is, the atoms, the molecules, or the ion that make up the phase carry out so in a continual manner throughout the phase. Scientific research recognizes three steady phases: the solid phase, in which separation, personal, instance particles have the right to be assumed of as in contact and held in place; the liquid phase, in which individual particles are in contact however moving v respect to every other; and also the gas phase, in which separation, personal, instance particles room separated indigenous each various other by relatively big distances (see number 8.1.1). no all building material will readily exhibit all phases. Because that example, carbon dioxide does not exhibit a fluid phase unless the press is higher than about six times common atmospheric pressure. Other substances, especially complicated organic molecules, might decompose at greater temperatures, rather than coming to be a fluid or a gas.

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For many substances, over there are various arrangements the particles have the right to take in the hard phase, relying on temperature and also pressure.

Which step a substance adopts depends on the pressure and the temperature that experiences. Of these 2 conditions, temperature sport are an ext obviously pertained to the phase of a substance. Once it is an extremely cold, H2O exists in the solid type as ice. Once it is warmer, the liquid phase the H2O is present. At even greater temperatures, H2O boils and also becomes steam.

Pressure transforms can also impact the visibility of a particular phase (as we indicated for carbon dioxide), but its impacts are less evident most the the time. We will mostly emphasis on the temperature impacts on phases, mentioning pressure results only once they space important. Many stayinfiji.comical substances monitor the exact same pattern the phases once going native a low temperature to a high temperature: the heavy phase, then the fluid phase, and then the gas phase. However, the temperature at which this phases are current differ for every substances and can be fairly extreme. Table \(\PageIndex1\) mirrors the temperature ranges for solid, liquid, and also gas phases for 3 substances. Together you have the right to see, there is too much variability in the temperature ranges.

Table \(\PageIndex1\): Temperature ranges for the 3 Phases of miscellaneous Substances SubstanceSolid phase BelowLiquid step AboveGas step Above The melting point the a problem is the temperature that separates a solid and also a liquid. The boiling point that a substance is the temperature the separates a liquid and also a gas.
hydrogen (H2) −259°C −259°C −253°C
water (H2O) 0°C 0°C 100°C
sodium chloride (NaCl) 801°C 801°C 1413°C

What accounts for this variability? Why carry out some substances become liquids at an extremely low temperatures, while others require really high temperatures prior to they end up being liquids? that all relies on the toughness of the intermolecular forces (IMF) between the particles that substances and also the kinetic energies (KE) of its molecules. (Although ionic compounds room not composed of discrete molecules, we will certainly still use the term intermolecular to include interactions in between the ion in such compounds.) building materials that endure strong intermolecular interaction require higher temperatures to come to be liquids and, finally, gases. Substances that endure weak intermolecular interactions do not need much energy (as measure up by temperature) to end up being liquids and gases and will exhibit these phases in ~ lower temperatures.

Figure \(\PageIndex1\): Transitions in between solid, liquid, and gaseous states of a substance happen when problems of temperature or push favor the associated changes in intermolecular forces. (Note: The room between particles in the gas step is much better than shown.)

Covalent Network Materials

Substances v the highest melting and also boiling points have actually covalent network bonding. This type of intermolecular communication is actually a covalent bond. In this substances, every the atom in a sample are covalently external inspection to one another; in effect, the whole sample is essentially one gigantic molecule. Plenty of of these substances are solid end a large temperature selection because the takes a lot of of energy to disrupt every the covalent bonds at once. One instance of a problem that mirrors covalent network bonding is diamond (Figure \(\PageIndex2\)). Diamond is composed completely of carbon atoms, every bonded to four other carbon atom in a tetrahedral geometry. Melting a covalent network heavy is not accomplished by overcoming the relatively weak intermolecular forces. Rather, all of the covalent bonds must be broken, a process that requires extremely high temperatures. Diamond, in fact, does no melt at all. Instead, that vaporizes to a gas at temperatures above 3,500°C. Diamond is extremely hard and is one of the couple of materials that can cut glass.

Figure \(\PageIndex2\): Diamond. Diamond, a form of pure carbon, has covalent network bonding. The takes a very high temperature—over 3,500°C—for diamond to leave the solid state. Source: picture © Thinkstock

Ionic Compounds

The strongest force between any two corpuscle is the ionic bond, in which two ions of the contrary charge space attracted to every other. Thus, ionic interactions in between particles are another kind of intermolecular interaction. Substances the contain ionic interaction are fairly strongly organized together, so this substances typically have high melting and boiling points. Salt chloride (Figure \(\PageIndex3\)) is an example of a substance whose particles suffer ionic interactions (Table \(\PageIndex1\)). This attractive pressures are periodically referred to together ion-ion interactions.

api/deki/files/137594/CNX_stayinfiji.com_10_01_IntravInter.jpg?revision=1&size=bestfit&width=431&height=169" />Figure \(\PageIndex4\): Intramolecular pressures keep a molecule intact. Intermolecular forces hold multiple molecules together and also determine many of a substance’s properties.

In this section, we will comment on the three types of IMF in molecular compounds: dipole-dipole, hydrogen bonding and London dispersion forces.

Dipole-dipole Intermolecular Forces

As debated in ar 4.4, covalent link that has actually an unequal sharing of electrons is called a polar covalent bond. (A covalent link that has an same sharing the electrons, together in a covalent bond with the very same atom on every side, is dubbed a nonpolar covalent bond.) A molecule through a net unequal distribution of electron in that covalent binding is a polar molecule. HF is an example of a polar molecule (see figure 8.1.5).

Figure \(\PageIndex5\): Polar Covalent Bonds. The electrons in the HF molecule are not equally common by the 2 atoms in the bond. Due to the fact that the fluorine atom has nine protons in that is nucleus, it attractive the negatively charged electrons in the bond an ext than the hydrogen atom does through its one proton in that is nucleus. Thus, electron are more strongly attractive to the fluorine atom, resulting in an imbalance in the electron distribution between the atoms. The fluorine next of the bond picks up a partial overall an adverse charge (represented through the δ− in the diagram), while the hydrogen next of the bond has actually an overall partial hopeful charge (represented by the δ+ in the diagram). Together a link is dubbed a polar covalent bond.

The charge separation in a polar covalent bond is not as extreme as is found in ionic compounds, yet there is a connected result: oppositely charged ends of different molecules will lure each other. This type of intermolecular communication is dubbed a dipole-dipole interaction. Countless molecules through polar covalent bonds endure dipole-dipole interactions.

The covalent bond in some molecules room oriented in space in together a method that the binding in the molecules cancel each various other out. The separation, personal, instance bonds room polar, however due to molecular symmetry, the as whole molecule is not polar; rather, the molecule is nonpolar. together molecules experience small or no dipole-dipole interactions. Carbon dioxide (CO2) and also carbon tetrachloride (CCl4) are examples of together molecules (Figure \(\PageIndex6\)).

Figure \(\PageIndex6\): Nonpolar Molecules. Return the individual bonds in both CO2 and also CCl4 are polar, their effects cancel out because of the spatial orientation of the bonds in each molecule. Together a result, such molecules experience tiny or no dipole-dipole interaction.

Recall indigenous the part 4.4 and also 4.5, top top stayinfiji.comical bonding and molecular geometry that polar molecules have actually a partial optimistic charge on one side and also a partial negative charge top top the other side that the molecule—a separation of charge referred to as a dipole. consider a polar molecule such as hydrogen chloride, HCl. In the HCl molecule, the an ext electronegative Cl atom bears the partial an adverse charge, vice versa, the less electronegative H atom bears the partial confident charge. One attractive force in between HCl molecules results from the attraction between the positive finish of one HCl molecule and also the an unfavorable end the another. This attractive pressure is referred to as a dipole-dipole attraction—the electrostatic force between the partly positive finish of one polar molecule and also the partially negative end of another, as shown in figure \(\PageIndex7\).

figure \(\PageIndex7\): This image shows two arrangements the polar molecules, such as HCl, that enable an attraction in between the partial an adverse end the one molecule and the partial positive finish of another.

The result of a dipole-dipole attraction is apparent when we compare the properties of HCl molecules to nonpolar F2 molecules. Both HCl and F2 consists the same number of atoms and also have approximately the exact same molecular mass. At a temperature the 150 K, molecules of both substances would have the same median kinetic energy. However, the dipole-dipole attractions between HCl molecules are enough to cause them to “stick together” to form a liquid, conversely, the relatively weaker dispersion forces in between nonpolar F2 molecules are not, and also so this substance is gas at this temperature. The higher normal boiling allude of HCl (188 K) compared to F2 (85 K) is a have fun of the greater strength of dipole-dipole attractions between HCl molecules, compared to the attractions between nonpolar F2 molecules. Us will often use worths such together boiling or freeze points as indicators of the family member strengths the IMFs of attraction existing within various substances.

Hydrogen Bonding Intermolecular Forces

Molecules through hydrogen atoms bonded to electronegative atom such together O, N, and F tend to exhibition unusually solid intermolecular interactions as result of a specifically strong kind of dipole-dipole attraction referred to as hydrogen bonding. The very large difference in electronegativity in between the H atom (2.1) and also the atom come which that is bonded (4.0 because that an F atom, 3.5 because that an O atom, or 3.0 because that a N atom), combined with the very little size that a H atom and also the relatively small size of F, O, or N atoms, leader to highly concentrated partial charges with this atoms. Due to the fact that the hydrogen atom does no have any kind of electrons various other than the ones in the covalent bond, the positively charged nucleus is almost completely exposed, allowing solid attractions to other nearby lone pairs of electrons.

Examples of hydrogen bonds include HF⋯HF, H2O⋯HOH, and H3N⋯HNH2, in i beg your pardon the hydrogen bonds room denoted by dots. Number \(\PageIndex8\) illustrates hydrogen bonding between water molecules. The physics properties that water, which has actually two O–H bonds, are strongly affected by the presence of hydrogen bonding between water molecules. Most molecular link that have a mass comparable to water space gases in ~ room temperature. However, since of the solid hydrogen bonds, water molecules space able to continue to be condensed in the liquid state.

figure \(\PageIndex8\): Water molecules take part in multiple hydrogen-bonding interactions with adjacent water molecules.

A hydrogen bond is one intermolecular attractive force in which a hydrogen atom, the is covalently bonded to a small, highly electronegative atom, is attractive to a lone pair of electrons on an atom in a bordering molecule. Number \(\PageIndex9\) shows just how methanol (CH3OH) molecules experience hydrogen bonding. Methanol includes both a hydrogen atom attached come O; methanol have the right to thus type hydrogen bond by acting as either a hydrogen shortcut donor or a hydrogen bond acceptor (lone pair). The hydrogen-bonded framework of methanol is as follows:

number \(\PageIndex9\): Methanol molecules take part in many hydrogen-bonding interaction with surrounding water molecules.

Despite use of words “bond,” save in mind that hydrogen bonds are intermolecular attractive forces, no intramolecular attractive forces (covalent bonds). Hydrogen bond are much weaker 보다 covalent bonds, however are usually much more powerful than other dipole-dipole attractions and also dispersion forces.

Effect of Hydrogen Bonding on boiling Points

Consider the compound dimethylether (CH3OCH3), ethanol (CH3CH2OH), and propane (CH3CH2CH3). Your boiling points, no necessarily in order, room −42.1 °C, −24.8 °C, and also 78.4 °C. Match each compound with its boil point. Describe your reasoning.


The shapes of CH3OCH3, CH3CH2OH, and CH3CH2CH3 space similar, as space their molar masses (46 g/mol, 46 g/mol, and 44 g/mol, respectively), so they will certainly exhibit comparable dispersion forces. Since CH3CH2CH3 is nonpolar, it might exhibit only dispersion forces. Because CH3OCH3 is polar, the will likewise experience dipole-dipole attractions. Finally, CH3CH2OH has actually an −OH group, and so the will suffer the uniquely strong dipole-dipole attraction recognized as hydrogen bonding. So the ordering in terms of strength of IMFs, and also thus cook points, is CH3CH2CH3 3OCH3 3CH2OH. The boiling suggest of propane is −42.1 °C, the boiling point of dimethylether is −24.8 °C, and also the boiling allude of ethanol is 78.5 °C.

Hydrogen Bonding and DNA

Deoxyribonucleic mountain (DNA) is discovered in every life organism and contains the hereditary information that determines the organism’s characteristics, gives the blueprint for making the proteins necessary for life, and also serves as a layout to happen this info on to the organism’s offspring. A DNA molecule consists of 2 (anti-)parallel chain of repeating nucleotides, which type its well-known dual helical structure, as shown in figure \(\PageIndex10\).

Figure \(\PageIndex10\): Two separate DNA molecules form a double-stranded helix in which the molecule are held together via hydrogen bonding. (credit: alteration of work by Jerome Walker, Dennis Myts)

Each nucleotide includes a (deoxyribose) sugar bound come a phosphate team on one side, and also one of 4 nitrogenous bases top top the other. 2 of the bases, cytosine (C) and thymine (T), room single-ringed structures known as pyrimidines. The other two, adenin (A) and also guanine (G), space double-ringed structures called purines. This bases kind complementary basic pairs consists of one purine and also one pyrimidine, with adenine pairing with thymine, and also cytosine with guanine. Each base pair is held together through hydrogen bonding. A and T share 2 hydrogen bonds, C and also G re-publishing three, and both pairings have a comparable shape and structure figure \(\PageIndex11\)

number \(\PageIndex11\): The geometries the the basic molecules result in maximum hydrogen bonding between adenine and also thymine (AT) and also between guanine and also cytosine (GC), so-called “complementary basic pairs.”

The cumulative effect of numerous hydrogen bonds properly holds the two strands of DNA together. Importantly, the two strands that DNA can relatively easily “unzip” under the middle due to the fact that hydrogen bond are reasonably weak contrasted to the covalent binding that hold the atoms of the separation, personal, instance DNA molecules together. This permits both strands to function as a design template for replication.

Example \(\PageIndex3\)

Order the following compounds of a team 14 element and also hydrogen from shortest to greatest boiling point: CH4, SiH4, GeH4, and also SnH4. Describe your reasoning.


Applying the skills acquired in the thing on stayinfiji.comical bonding and also molecular geometry, all of these compounds room predicted to be nonpolar, therefore they may experience only dispersion forces: the smaller sized the molecule, the less polarizable and also the weaker the dispersion forces; the bigger the molecule, the bigger the dispersion forces. The molar masses the CH4, SiH4, GeH4, and also SnH4 are roughly 16 g/mol, 32 g/mol, 77 g/mol, and 123 g/mol, respectively. Therefore, CH4 is expected to have the shortest boiling allude and SnH4 the highest possible boiling point. The notified from shortest to highest boiling allude is supposed to be

CH4 4 4 4

A graph that the really boiling points of this compounds matches the period of the group 14 elementsshows this forecast to be correct:


Example \(\PageIndex4\): Intermolecular Forces

What intermolecular forces besides dispersion forces, if any, exist in every substance? Are any of these substances solids at room temperature?

potassium chloride (KCl) ethanol (C2H5OH) bromine (Br2)


Potassium chloride is written of ions, so the intermolecular communication in potassium chloride is ionic forces. Since ionic interactions space strong, it might be supposed that potassium chloride is a solid in ~ room temperature. Ethanol has a hydrogen atom attached come an oxygen atom, so it would suffer hydrogen bonding. If the hydrogen bonding is solid enough, ethanol might be a solid at room temperature, however it is challenging to understand for certain. (Ethanol is actually a fluid at room temperature.) elemental bromine has two bromine atoms covalently bonded to every other. Since the atoms on either next of the covalent bond are the same, the electron in the covalent bond are common equally, and also the link is a nonpolar covalent bond. Thus, diatomic bromine does not have any type of intermolecular forces other 보다 dispersion forces. That is i can not qualify to it is in a solid in ~ room temperature unless the dispersion pressures are solid enough. Bromine is a liquid at room temperature.

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Key Takeaways

A phase is a form of issue that has the exact same physical properties throughout. Molecules connect with each other through various forces: dipole-dipole interactions, hydrogen bonding, and also dispersion forces. Dipole-dipole attractions result from the electrostatic attraction that the partial negative end of one dipolar molecule for the partial positive end of another. Hydrogen bonds are a special form of dipole-dipole attraction the results as soon as hydrogen is external inspection to among the three most electronegative elements: F, O, or N. The short-lived dipole that outcomes from the movement of the electron in an atom can induce a dipole in an surrounding atom and also give increase to the London dispersion force. London pressures increase with enhancing molecular size.