Ionic compounds intermolecular forces

The degree of polarity has considerable influence on the physical properties of covalent compounds and it can also affect chemical reactivity. The melting point (mp) and boiling point (bp) are higher in ionic substances due to the strong nature of the interionic forces, whereas the covalent compounds have lower values due to the weak nature of intermolecular forces. 

It should be noted that in ionic compounds the interionic forces are much stronger than the intermolecular forces in simple covalent substances and so the melting and boiling points are generally higher. 

FIGURE 7.4 Of the 16 chemistry topics examined (1-16) on the final exam, overall the POGIL students had more correct responses to the same topics than their L-I counterparts. Some topics did not appear on all the POGIL exams. Asterisks indicate topics that were asked every semester and compared to the L-I group. The topics included a solution problem (1), Lewis structures (2), chiral center identification (3), salt dissociation (4), neutralization (5), acid-base equilibrium (6), radioactive half-life (7), isomerism (8), ionic compounds (9), biological condensation/hydrolysis (10), intermolecular forces (11), functional group identification (12), salt formation (13), biomolecule identification (14), LeChatelier s principle (15), and physical/chemical property (16). 

Larger dipoles lead to stronger intermolecular forces. The species having dipole moment very nearly equal to the one predicted for ionic compounds do not condense to form molecular solids or liquids. 

The polarity of molecules like water has very significant effects on the behavior of these compounds. If you recall in ionic compounds, the oppositely charged ions attract each other and form large crystalline structures. A similar process occurs between polar molecules, but we describe these as intermolecular forces. There are three main intermolecular forces we need to examine. All three of these forces are known as van der Waals forces and are specifically called hydrogen-bonding forces, dipole-dipole interactions, and London dispersion forces. 

Answer The correct answer is SrCl2(s) —> SrCl2(/). Melting a stable ionic compound will require much more energy than breaking most intermolecular forces, especially the vaporization of an alcohol, choice 2, and the melting of a soft metal like gold. 

The correct answer is (B). NH3 has the weakest intermolecular forces of the other molecules. Diamond exists in a covalent network bond, sodium acetate is an ionic compound, and glycerine contains several C O and O H bonds (which allow hydrogen bonding). Silver has metallic bonds while ammonia, NH3, is only held together by fairly weak hydrogen bonds (the N-H bond is not very polar). 

You have learned that pure covalent compounds are not held together by ionic bonds in lattice structures. They do form liquids and solids at low temperatures, however. Something must hold the molecules together when a covalent compound is in its liquid or solid state. The forces that bond the atoms to each other within a molecule are called intramolecular forces. Covalent bonds are intramolecular forces. In comparison, the forces that bond molecules to each other are called intermolecular forces. 

A solid covalent compound has both intermolecular and intramolecular forces. Do solid ionic compounds contain intermolecular forces Explain your answer. 

Table 13.2 shows some of the properties of the trihalides of the Group VA elements. Several trends in the data shown in Table 13.2 are of interest. For example, the trihalides of phosphorus and arsenic can be considered as covalent molecules. As a result, the intermolecular forces are dipole-dipole and London forces that are weak. Therefore, the melting and boiling points increase with molecular weight as expected. The trifluorides of antimony and bismuth are essentially ionic compounds and the melting points are much higher than those of the halogen derivatives that are more covalent. 

Ionic compounds do not have a smell because the charged particles are held together strongly and do not allow any of their particles to escape into a vapour (unlike covalent compounds, whose intermolecular forces are weaker, so some of their molecules escape as a vapour, hence they smell). 

Ionic compounds contain oppositely charged particles held together by extremely strong electrostatic interactions. TThese ionic interactions are much stronger than the intermolecular forces present between covalent molecules, so it takes a great deal of energy to separate oppositely charged ions from each other. 

Differences in properties are a result of differences in attractive forces. In a covalent compound, the covalent bond between atoms in molecules is quite strong, but the attraction between individual molecules is relatively weak. The weak forces of attraction between individual molecules are known as inter-molecular forces, or van der Waals forces. Intermolecular forces, which are discussed at length in Chapter 13, vary in strength but are weaker than the bonds that join atoms in a molecule or ions in an ionic compound. 

The chemical structure of a typical divalent metal acetylacetonate, for which the abbreviation would be M(acac)j. These compounds are internally bonded ionically and complexed to oxy en at the same time Thus, their intramolecular forces are very strong (they are stable), but their intermolecular forces are weak (they are volatile). 

Compound 25 has been synthesized by Reetz et al. (82, 83). It has been used to complex ionic pair species such as KF. The potassium ion is complexed by the crown ether and the fluoride ion is held by a combination of orbital overlap with the Lewis acidic boron atom and electrostatic attraction to the positively charged potassium. This receptor provides an elegant example of the use of a combination of intermolecular forces. 

The behavior of molecular compounds is more varied. Some—for example, CO, CO2, HCl, NH3, and CH4 (methane)—are gases, but the majority of molecular compounds are liquids or solids at room temperature. However, on heating they are converted to gases much more easily than ionic compounds. In other words, molecular compounds usually boil at much lower temperatures than ionic compounds do. There is no simple rule to help us determine whether a certain molecular compound is a gas under normal atmospheric conditions. To make such a determination we need to understand the nature and magnitude of the attractive forces among the molecules, called intermolecular forces (discussed in Chapter 11). In general, the stronger these attractions, the less likely a compound can exist as a gas at ordinary temperatures. 

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