Intermolecular Attraction Forces - Essay Example

Intermolecular Attraction Forces Intermolecular attraction Forces are a force of attraction between close particles such as in molecules, ions or the atoms. Intermolecular forces are much weaker as compared with intramolecular forces which are the force of attraction inside the molecules or particles. The type of intermolecular attractive force between particles defines their physical properties. Physical properties such as melting point, boiling point, surface tension, evaporation, solubility, and viscosity usually depends on the intermolecular attractive force. These properties are used to measure the strength of intermolecular forces of attraction between particles (Bettelheim et al. 151). For an instant, when bonds between particles are made more polar, the particle charges increases resulting to stronger intermolecular forces which lead to high melting and boiling points. In chemistry, there are four types of intermolecular attractive forces. They include ionic forces, hydrogen bonding, dipole forces, and London Dispersion forces. The attractive forces tend to be similar to the type bonding particles within a molecule. The intermolecular forces, therefore, follow the patterns of the type bonding between molecules. In addition, the nature of intermolecular attractive forces between molecules creates the difference between gasses, liquids, and the solids (Bettelheim et al. 152). Ionic forces Ionic forces are the strongest attractive forces among the intermolecular forces. They are referred as electrostatic forces and hold ions in solids together. The forces are due to cationic charges where unlike charges attract each other, and unlike charges repel. Ionic compounds form due to the interaction between negative and positive ions like in sodium chloride salt. Cations are usually metals and examples are Mg2+, Na+, Ca2+, Cu2+, and Zn2+ while anions are non-metals and include Cl-, Br-, O-, and F-. The balance between the force of attraction of both cation and anion result to the formation of the ionic bond. Lattice energy forms when there is a balance between the force attractions within crystalline compounds. In ionic intermolecular attractive force, there is a complete transfer of electrons from metals to non-metals where metals become positively charged while non-metals are negatively charged. Metals have a tendency to lose electrons because they have few electrons in the outermost energy level. Ionization energy is spent to remove electrons and form ions (Bettelheim et al. 154). However, non-metals have a high affinity for electrons hence they gain electrons to form anions. The charge difference determines the strength of the attractive force. The attraction force is stronger when the charge difference is greater. Below is an example of an ionic force of attraction between sodium and chlorine. Na+1 → ← Cl-1 ↑ opposite charges attract each other forming ionic force. Dipole Forces Some molecules have two poles, and they are referred as dipole molecules. The molecules fall between the covalent and ionic bonds extremes. They are polar molecules which are covalent in nature. One pole or end of the molecule have positive partial charge while the other opposite end has a partial negative charge. The electronegativity of atoms is very high such that electrons are shared unequally hence they are drawn towards one atom. The molecules position themselves in a way that unlike partial charges attract each other and operates efficiently. An example of a polar intermolecular attractive force is hydrochloric acid. The acid has hydrogen with positive partial charge and a chloride with a partial negative charge. These network of partial positive and negative charges attract molecules together. Polar compounds forms when two non-metals fail to share electrons equally between them. A well-known example is the carbon and hydrogen combination in organic compounds where there is the formation of partial charges. Some non-metal have an affinity for other electrons while they keep their electrons and when it is not successful, and it result in the formation of partial charges. Water is also a polar molecule experiencing dipole force of attraction. This property makes both chemical and physical properties of water unique. Water also forms a covalent structure which involves sharing of electrons. The two atoms do not loose electrons completely unlike in ionic forces. Hydrogen Bonding Hydrogen bond is a dipole force which is of a special case. It is an attractive force where hydrogen is attached to two electronegative atoms which are of different molecules. Oxygen, nitrogen, or fluorine are usually the electronegative atoms. It means that hydrogen atom may be attached to a molecule of oxygen or nitrogen which is attracted to a different molecule of oxygen or nitrogen like in the water (Bettelheim et al. 152). In water, the oxygen has a lone pair of electrons where two dissimilar bonds to each oxygen can be made. During the formation of the hydrogen bond, the atom which is electronegative must possess one or more electron pairs which are unshared. Nitrogen and oxygen are examples. Hydrogen usually has partial charges and attempts to find atom with free electrons to share with nitrogen and oxygen. Hydrogen is therefore attracted to a partial negative charge resulting in the formation of the hydrogen bond. Hydrogen bond is stronger compared with dipole forces between atoms of different molecules. Although the bond is not as strong as a covalent bond, the hydrogen bond is known to affect water properties. Water is good example of hydrogen bonding where one water molecule can form a maximum of four hydrogen bonds with the neighboring molecules of water. The boiling point of water is higher than that of ammonia and hydrogen fluoride because of hydrogen bonding. A group of water molecules has more lone pairs of electrons on oxygen as compared with ammonia where nitrogen has limited number of lone pairs. As a result, ammonia can only form one hydrogen bond hence low boiling point compared to water which forms four hydrogen bonds (Bettelheim et al. 155). Induced dipole forces or London Dispersion forces The induced dipole intermolecular forces are the weakest among the attractive forces. They are also referred as London Dispersion forces. The forces involve non-polar molecules where shifting of electron clouds result to the formation of temporary dipoles within molecules. The electron cloud of neighboring non-polar particles is attracted or repelled by these temporary dipoles. The force of attraction only lasts for a moment where temporary dipoles can only exist for a few seconds. Due to the instantaneous formation of dipoles, distribution of electrons becomes asymmetrical where new dipoles are formed that are attracted to each other. The strength of dipole forces depends on how ease electron clouds are distorted. All diatomic molecules are covalently bonded and are non-polar (Bettelheim et al. 154). Examples of non-polar compounds include iodine and oxygen. Two iodine atoms share two electrons while in oxygen result to total sharing of four electrons to form polar compounds with electron clouds. The induced dipole intermolecular forces are present in all molecules because all molecules have an electron cloud. The nature of the attractive force relies on the number of electrons in the molecule where the more the electrons, the stronger the force. In addition, an increase in polarity increases the strength of the attractive forces. Hydrocarbons stick together due to induced dipole forces (Bettelheim et al. 153). However, in alkanes increase in chain length increases their boiling point. For example, methane has a boiling point of -164 o C while octane has a boiling point of 125 o C. In general, the intermolecular forces are a force of attraction that keeps molecules together. The forces determine the physical properties of particles. The ionic forces are the strongest then followed by hydrogen bonding. The dipole-dipole forces are the third in terms of strength while the London dispersion are the weakest. The ionic compounds, therefore, have the highest melting and boiling points because they require a lot of energies to break the strong ionic bonds between molecules. However, the vapor pressure of compounds reduces with an increase in intermolecular attractive forces. The ionic compounds have lowest vapor pressure compared with non-polar which have the highest (Bettelheim et al. 152). The intermolecular attractive force depicts the differences between gas, solids, and liquids due to competition between thermal energy and intermolecular forces. The intermolecular attractive force has an effect on solubility as well. Non-polar compounds dissolve only in solvents that are non-polar. Non-polar solute such as paraffin do not dissolve in ethanol and water since they are polar. Additional, polar compounds such as glucose dissolves specifically only to polar solvents like water. However, ionic solutes do not dissolve to non-polar but only to polar solvents. Work Cited Bettelheim, William Brown, Mary Campbell, Shawn Farrell and Omar Torres. Introduction to General Organic and Biochemistry. New York: Cengage Learning, 2012. Print. Read More