Types and Effects of Intermolecular Forces of Attraction PDF

Kinetic Molecular Theory Intermolecular Forces of Attraction Kinetic Molecular Model of Liquids and Solids Kinetic Molecular Theory of Matter: - states that matter is composed of a very large number of very tiny particles or ions; - particles are constant...

Kinetic Molecular Theory Intermolecular Forces of Attraction Kinetic Molecular Model of Liquids and Solids Kinetic Molecular Theory of Matter: - states that matter is composed of a very large number of very tiny particles or ions; - particles are constantly in motion and possess energy of motion (kinetic energy) that we perceive as temperature; - temperature decreased = molecules of a gas can be condensed to liquid and then to solid; - slowly moving molecules are attracted to each other easily ---> condensed phases: liquid and soldi; - ionic compounds never exist as gasses since very high temperature is required in overcoming strong electrostatic attraction between the ions; - physical state of the compound = temperature, kinetic energy intermolecular forces. Kinetic Molecular Theory and Physical States: Gaseous State: Gas has high speed molecules. *Kinetic Molecular Theory of Matter and the Theory of Heat = molecules are in constant motions, but they only stop moving when temperature reaches Absolute Zero, 0 K. Kinetic energy in gas molecules > intermolecular attractive forces between them ---> gas molecules will easily spread to space given to it and not stay in an open container and described by following characteristics: - compose of very large number of molecules move in straight lines; their direction is random; - molecules are small (volume they occupy is small compared to the total volume); - molecules do not attract or repel each other (no strong intermolecular forces); - elastic collision (they take place within a negligible span of time and does not lose kinetic energy;  - average kinetic energy is proportional to temperature (Kelvin, K). Liquid State: Liquids have slower molecules which roll over each other. *gas molecules ---> cooled sufficiently ---> molecules with less kinetic energy and are moving slower = intermolecular forces take over and molecules are attracted to each other. This mild binding force holds the material together in the form of a liquid state with following characteristics: - particles in continuous, random motion while maintain the volume; - volume is dependent on the size of the particles and effect the properties of a liquid; - slow motion and kinetic energy of the particles = intermolecular forces are present and significantly affect the properties of the liquid; - fixed volume but take the shape of the container and gravity pulls the liquid molecules down to the bottom. Solid State: Particles in solid can only vibrate. *liquid is cooled even more ---> particles slow down so much that they stuck in the structure of a solid = particles are not moving freely, simply voibrating in place and have the following characteristics: - closely packed particles in vibration and fixed locations = fixed volume and shape; - volume is dependent on the size of the particles and effect on their properties; - slow vibration (almost no kinetic energy of particles) ---> strong effect of intermolecular forces to the properties; - fixed volume and shape. Activity: Draw and arrange the three physical states of matter in order of increasing volume of empty space between its particles. Intermolecular Forces of Attraction Difference between Intramolecular Forces and Intermolecular Forces of Attraction: Intramolecular Forces: - forces inside a molecule holding atoms together; - within molecules (chemical bonds: ionic and covalent); - stronger force of attraction between atoms. Intermolecular Forces: - forces between molecules, holding molecules together; - weaker force of attraction between molecules. Types of Intermolecular Forces of Attraction: Ion-Dipole Force: - attraction between an ion (cation or anion) and a nearby polar molecule (a dipole); - attraction of ions to the oppositely charged ends of the polar molecules is greater than the attraction between the ions themselves; - solubility of ionic compounds in water (a polar molecule); - separation of ions from each other, then the water molecules will cluster around it. - example: solubility of sodium chloride (NaCl, table salt) in water Van Der Waals Forces: Dipole-Dipole Force: - forces exist between polar (a dipole) molecules; - between polar molecules, one end of a dipole attracts the oppositely charged end of the other dipole. - example: attraction between hydrogen chloride (HCl) molecules Dispersion (London) Forces: - force of attraction between a nonpolar molecule with instantaneous dipole and another nonpolar molecule with induced dipole; - weak momentary force between temporary dipole and induced dipole; - dominat type between identical diatomic molecules such as O2, N2, Cl2.  - example: attraction between chlorine gas (Cl2) molecules Charged-Induced Dipole Force: - the charge of the ion or a polar molecule (a dipole) causes distortion of the electron cloud in the nonpolar molecule,, resulting a short partial charge; - charge species (ion or permanent dipole) ---> distortion of the electron cloud ---> induced dipole of nonpolar molecule; - nature of the charged species: > ion – induced dipole > dipole – induced dipole - example: when an Argon (Ar) atom approaches a hydrogen chloride molecule (polar) the electrons can move to one side of the nucleus resulting in a very modest dipole moment that lasts barely a fraction of a second Hydrogen Bonding: - exists between a hydrogen atom bound to a small and highly electronegative non-metal atom and another electronegative atom in another molecule; - the type of interaction which can be only participated by Nitrogen (N), Oygen (O), and Fluorine (F) atoms; - generally stronger than the ordinary dipole-dipole force and dispersion force; weaker than covalent bond and an ionic bond. - example: hydrogen bonding in water where a water molecule contains a highly electronegative oxygen atom linked to the hydrogen atom From Weakest to Strongest: Intermolecular Forces (Waekest) - Dispersion (London) Force - Charged-Induced Dipole Force - Dipole-Dipole Force - Hydrogen Bonding - Ion-Dipole Force Intramolecular Forces (Strongest) - Ionic Bonds - Covalent Bonds DECREASING STRENGTH Intermolecular Forces of Attraction and Properties of Substances: Gases: - weak intermolecular forces = diffuse easily, no definite shape and volume; - have negligible intermolecular forces existing between their molecules. Liquids: - fluidity and viscosity (resistance of a liquid to flow): > stronger intermolecular forces = higher viscosity (more viscous) - surface tension (toughness of the surface of a liquid): > stronger intermolecular forces = higher surface tension - vapour pressure (small amount of gas that is found above all liquids): > stronger intermolecular forces = lower vapour pressure - boiling and melting point (molecules stick together more, they will be tougher to break apart): > stronger intermolecular forces = higher boiling and melting point = more energy required Solids: - strong attractive forces in the particles = nearly incompressible, do not flow; - solid particles only vibrate at fixed positions. Activity: Identify the type of intermolecular force associated within the given statements: 1. Ammonia (NH3) molecules contains highly electronegative atom Nitrogen (N) linked to Hydrogen (H) atoms. _________________ 2. When a Xenon (Xe) atom approaches a water (H2O) molecule. Electrons in Xenon (Xe) atom positioned on one side of the nucleus at any given time, resulting in a partially positive charge on one end and a partially negative charge on the other. As a result, the Xenon (Xe) atom creates an immediate dipole. _________________ 3. Force that may exist between interacting Iodine (I2) gas molecules. __________________ 4. Interaction of Hydrogen Fluoride (HF) molecules with each other. _________________ 5. Formation of ions from an ionic compound when dissolved in water. __________________ *Any molecules that experience one type of attraction, also experience all the weaker types of attractions. Example: Hydrogen chloride (HCl) molecules experience the Dipole- Dipole and Dispersion (London) forces of attraction.