chem

• Kinetic Molecular Theory (KMT)


  1. All matter is comprised of small particles

  2. The molecules interact with one another through attractive forces. The strength of these forces is related to the distance between the particles.

  3. These molecules are always in constant random motion.

  4. The temperature of a substance is a measure of the average kinetic energy of the molecules.

  
• Nuclear model


  Inside the nucleus contains the proton (positive charge) and neutron (neutral), while outside the nucleus are the electrons (negative charge)
• All matter is comprised of small particles
• Atoms


  The building blocks of matter
• Molecules


  Matter can also exist as Molecules
• Intermolecular forces


  The attractive forces between molecules
• The stronger the interaction between two molecules

  The smaller their distance will be
• Molecular force of molecules

  Inversely proportional to the distance of the molecules
• Substances with intermolecular forces

  • Intermediate to strong intermolecular forces will form a condensed phase (either solid or liquid)

  Weak intermolecular forces will be in the gaseous state
• At lower temperatures


  Intermolecular forces determine the state of a substance
• At high temperatures


  Molecules have higher kinetic energy and will be able to overcome the intermolecular forces present
• Solid


  • Particles have strong intermolecular forces such that their particles are very close to one another

  Restricted motion, only able to vibrate back and forth around a specific point or location
• Liquid


  • Particles have intermediate intermolecular forces, farther from one another compared to solids

  Able to move past each other, but motion is restricted to small distances as they will collide with another molecule
• Gas


  • Particles are very far apart from one another due to weak intermolecular forces

  Able to move in relatively long distances before colliding with another molecule
• Solid


  • Fixed shape, fixed volume, virtually incompressible
• Liquid


  • Depends on the container, fixed volume, only slightly compressible
• Gas


  • Depends on the container, assumes the volume of the container, very compressible
• All molecules are in constant random motion
• Increasing the temperature


  Weakens the intermolecular forces of attraction
• Melting


  Molecules in ice vibrate back and forth to a specific location (solid phase)

  Increasing temperature provides enough kinetic energy to overcome strong intermolecular forces

  Solid becomes a liquid
• Vaporization


  Liquid water particles are able to move past one another in relatively longer distances

  Liquid is converted to a gas
• Intermolecular forces (IMFs)


  Attractive forces present in between molecules
• Ions


  Charged particles
• Polar molecules


  Molecules with two charges (positive and negative)
• Cations


  Positively charged ions
• Anions


  Negatively charged ions
• Four main types of Intermolecular Forces of Attraction

  • London Dispersion Forces

  Dipole-dipole forces

  Ion-dipole forces

  Hydrogen bonding

  
• Van der Waals forces


  London dispersion forces and dipole-dipole forces
• Ion-ion interaction


  Interaction between two oppositely charged particles, also known as ionic bonds
• Strength of ion-ion interactions


  Directly proportional to the product of the charges and inversely proportional to the distance between the particles
• Ion-dipole interaction


  Electrostatic attraction of a molecule containing a dipole and an ion
• Strength of ion-dipole interactions

  Depends on the charge density of an ion (larger surface area = weaker interaction, smaller surface area = stronger interaction)
• Dipole-dipole interactions


  Attractive forces present between polar molecules, result of electrical interactions among dipoles on neighboring molecules
• Hydrogen bonding


  Attractive force that exists when hydrogen is bonded to the most electronegative atoms (F, O, or N)

  A special kind of dipole-dipole force and one of the strongest types of IMFs

  Hydrogen bond donor is a molecule that provides the hydrogen atom

  Hydrogen bond acceptor is a molecule that contains the lone pair-bearing electronegative atom

  
• London dispersion forces (LDFs)


  The weakest type of IMFs, present in between all electrically neutral molecules

  Strength depends on the polarizability of the molecule (ease at which the electron cloud can be distorted)

  Caused by fluctuations in the electron distribution within atoms or molecules, resulting in a temporary dipole
• Induced dipoles


  Occur when a nonpolar atom becomes polar due to the presence of an ion or a dipole
• Phase


  A homogeneous state in which the substance has a uniform composition and is governed by the same intermolecular forces throughout the material
• Phase changes

  • Freezing - Liquid to Solid

  Melting - Solid to Liquid

  Boiling/Evaporation - Liquid to Gas

  Condensation - Gas to Liquid

  Deposition - Gas to Solid

  Sublimation - Solid to Gas
• When a solid/liquid transitions to a gas

  There is a decrease in the order in the material
• Enthalpy (ΔH)


  The amount of heat energy transferred from the surroundings to the substance

  Endothermic - Heat is absorbed (ΔH > 0)

  Exothermic - Heat is released (ΔH < 0)