Week 2 Forces of Attraction - Our Lady of Fatima University - PDF

OUR LADY OF FATIMA UNIVERSITY COLLEGE OF PHARMACY Valenzuela. Quezon City. Antipolo. Pampanga. Cabanatuan. Laguna FORCES OF ATTRACTION PPAR 211 Name of Faculty Instructor-...

OUR LADY OF FATIMA UNIVERSITY COLLEGE OF PHARMACY Valenzuela. Quezon City. Antipolo. Pampanga. Cabanatuan. Laguna FORCES OF ATTRACTION PPAR 211 Name of Faculty Instructor- College of Pharmacy  LEARNING OUTCOMES At the end of this unit, the students are expected to: 1. Understand the nature of the intra- and intermolecular forces that are involved in stabilizing molecular and physical structures. 2. Understand the differences in these forces and their relevance to different types of molecules. 3. Appreciate the differences in the strengths of the intermolecular forces that are responsible for the stability of structures in the different states of matter.  MOLECULAR FORCES Knowledge of these forces and their equilibrium is important in understanding the: 1. properties of gases, liquids, and gases 2. interfacial phenomena 3. flocculation in suspensions 4. stabilization of emulsions 5. compaction of powders in capsules 6. dispersion of powders or liquid droplets in aerosols 7. compression of granules to form tablets  MOLECULAR FORCES o Atoms aggregate to form molecules and lattices. Molecules aggregate to form condensed phases of matter. o The aggregation of atoms, appositively charged ions, and molecules are a consequence of electrical forces exerted on the electrons of one particle by the nucleus (or nuclei) of the other.  MOLECULAR FORCES There are 2 types of attraction in molecules: intramolecular & intermolecular forces of attraction  TWO BROAD CATEGORIES OF FORCES OF ATTRACTION I. Intramolecular II. Intermolecular o forces that exist within o forces of attraction that molecules or exist between the fundamental/formula molecules in a units (forces that hold compound. atoms or ions in a compound).  INTRAMOLECULAR FORCES I. Intramolecular Forces are forces within molecules that caused by the attraction and repulsion of charged particles. 1.Ionic or Electrovalent Bond - Electrostatic force of attraction between ions of opposite charge. 2. Covalent Bonds - Formed between atoms with a small difference in electronegativity. Polar covalent bond Nonpolar covalent bond 3. Metallic Bonds - Positive ions surrounded by a sea of mobile (delocalized) electrons. Strong electrostatic force of attraction binds the system together.  IONIC BOND A. Ionic Bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. ü Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal. ü Transfer of electrons between a non-metal and metal Na + Cl → Na+ + Cl− → NaCl  Properties of Ionic or Electrovalent Compounds o Crystalline solids- rigidity and strength o High melting and boiling points o Conduct electricity in a molten and aqueous state o They are hard o They are brittle o Soluble in polar solvents such as water (solute-solvent interactions)  IONIC BOND bond is formed by the complete transfer of valence electron(s) between atoms. generates two oppositely charged ions. metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively charged anion.  COVALENT BOND B. Covalent Bonds is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. 2 TYPES: Polar covalent bond Nonpolar covalent bond  POLAR COVALENT BOND A polar covalent bond is formed when atoms of slightly different electronegativities share electrons.  NONPOLAR COVALENT BOND A nonpolar covalent bond is formed between same atoms or atoms with very similar electronegativities— the difference in electronegativity between bonded atoms is less than 0.5.  Properties of Covalent Compounds o Liquids and gases at room temperature o Relatively low boiling point. o Do not conduct electricity o Insoluble in polar solvent o Soluble in non-polar solvent  METALLIC BONDING This type of covalent bonding specifically occurs between atoms of metals, in which the valence electrons are free to move through the lattice. This bond is formed via the attraction of the mobile electrons—referred to as sea of electrons—and the fixed positively charged metal ions. Metallic bonds are present in samples of pure elemental metals, such as gold or aluminum, or alloys, like brass or bronze. METALLIC BONDING  METALLIC BONDING Influences the strength of the bond: o Availability of electrons o More available delocalized electrons, the stronger the electrostatic attraction, the stronger the metallic bond. o Size of the charge on metal ion o Larger the charge size, the stronger the metallic bond.  INTERMOLECULAR FORCES II. Intermolecular Forces are the forces of attraction between molecules. üCohesion is the molecular attraction or joining of the surfaces of two pieces of the same substance. üAdhesion is any attraction process between dissimilar molecules that can potentially bring them in "direct contact".  REPULSIVE AND ATTRACTIVE FORCES When molecules interact, both repulsive and attractive forces operate. Attractive forces are inversely proportional to the distance of separation.  REPULSIVE AND ATTRACTIVE FORCES As two atoms or molecules are brought closer together, the opposite charges and binding forces in the two molecules are closer together than the similar charges and forces, causing the molecules to attract one another. The negatively charged electron clouds of molecules largely govern the balance (equilibrium) forces between the two molecules.  1. VAN DER WAALS FORCES Relate to non-ionic interactions between molecules yet they involve charge-charge interactions. Molecules frequently tend to align themselves with their neighbors, so that the negative pole of one molecule points toward the positive pole of the next. üKeesom üDebye üLondon  A. Keesom or Dipole-Dipole Forces ○ Dipole-dipole forces exist between polar molecules where the positive end of one molecule is attracted to the negative end of another molecule. ○ The greater the polarity (difference in electronegativity of the atoms in the molecule), the stronger the dipole-dipole attraction.  A. Keesom or Dipole-Dipole Forces o Dipole-dipole attractions are very weak and substances held together by these forces have low melting and boiling point temperatures. o Generally, substances held together by dipole- dipole attractions are gases at room temperature. o Named after Willem Hendrik Keesom.  A. Keesom or Dipole-Dipole Forces Keesom forces is also known as “Orientation Effect” In Keesom forces, permanent dipoles interact with one another with an ion-like fashion.  a. Keesom or Dipole-Dipole Forces Forces occur when the partially positively charged part of a molecule interacts with the partially negatively charged part of the neighboring molecule. The prerequisite for this type of attraction to exist is partially charged ions—for example, the case of polar covalent bonds such as hydrogen chloride. Dipole-dipole interactions are the strongest intermolecular force of attraction.  B. Debye or Dipole—Induced Dipole Forces ○ Permanent dipoles are capable of inducing an electric dipole in nonpolar molecules (which are easily polarizable) in order to produce dipole-induced dipole ○ This interaction is called the Debye force after Peter J.W. Debye.  C. London or Induced Dipole— Induced Dipole Forces o They result from the movement of the electrons in the molecule which generates temporary positive and negative regions in the molecule.  C. London or Induced Dipole— Induced Dipole Forces o Caused by correlated movements of the electrons in interacting molecules. The electrons, which belong to different molecules, start "feeling" and avoiding each other at the short intermolecular distances, which is frequently described as formation of "instantaneous dipoles" that attract each other.  c. London or Induced Dipole— Induced Dipole Forces o Nonpolar molecules can induce polarity in one another by induced dipole-induced dipole ,  c. London or Induced Dipole— Induced Dipole Forces The weakest intermolecular forces and exist between all types of molecules, whether ionic or covalent—polar or nonpolar. The more electrons a molecule has, the stronger the London dispersion forces are. For example, bromine, Br2.  2. ION-DIPOLE INTERACTION o Attractions that occur between ions and polar molecules. o These types of interactions account in part for the solubility of ionic crystalline substance in water.  3. ION-INDUCED DIPOLE INTERACTION o This is a weak attraction that results when the approach of an ion induces a dipole in an atom or in a nonpolar molecule by disturbing the arrangement of electrons in the nonpolar species.  3. ION-INDUCED DIPOLE INTERACTION o Ion-induced dipole forces are presumably involved in the formation of the iodide complex. o Solubility of iodine in KI is an example. I2 + KI = KI3  4. HYDROGEN BOND o The interaction between a molecule containing a hydrogen atom and a strongly electronegative atom such as fluorine, oxygen, or nitrogen is of particular interest. o Because of the small size of a hydrogen atom and its electrostatic field, it can move in close to the electronegative atom and form an electrostatic type of union known as a hydrogen bond or hydrogen bridge.  4. HYDROGEN BOND The partially positive end of hydrogen is attracted to the partially negative end of the oxygen, nitrogen, or fluorine of another molecule. Hydrogen bonding is a relatively strong force of attraction between molecules, and considerable energy is required to break hydrogen bonds.  4. HYDROGEN BOND Hydrogen bonding plays an important role in biology; hydrogen bonds are responsible for holding nucleotide bases together in DNA and RNA.  RELATIVE STRENGTH OF INTERMOLECULAR FORCES OF ATTRACTION Intermolecular Occurs between … Relative strength force Dipole-dipole Partially oppositely Strong attraction charged ions Hydrogen bonding H, atom and O, N/ or Strongest of the F atom dipole-dipole attractions London dispersion Temporary or Weakest attraction induced dipoles THANK YOU! ANY QUESTIONS?  References Sinko, P.J., Martin’s Physical Pharmacy and Pharmaceutical Sciences. Philadelphia, PA : Wolters Kluwer. 2017 Smith, B. Remington Education: Physical Pharmacy. London :Pharmaceutical Press. 2016a Atkins Elements of Physical Chemistry. 2017