CHEM 205 lecture 1

• Scientific method


  1. Observation

  2. Hypothesis

  3. Experiment

  4. Law

  5. Theory or model
• Quantitative observation


  Measuring things
• Intrinsic properties


  • Density
  • Melting point
  • Boiling point
  • Viscosity
• Extrinsic properties

  • Mass
  • Volume
  • Length
  • Width
  • Height
• Converting between temperature scales

  1. Kelvin: temp celcius + 273.15K

  2. Fahrenheit: (9/5 x C) + 32

  3. Celcius: (F – 32) x 5/9 OR K-273.15
• Random error

  Unavoidable, indeterminate error
• Systematic error


  Determinate, occurs in same direction each time, often results from poor technique
• Accuracy


  How close the value you got is to the accepted value
• Precision


  How close you are to all of the values obtained, using several measurements of the quantity, usually more decimal points
• Relative error


  (measured value – true value)/ true value , multiplied by 100 for %
• Standard deviation


  Measured value – average value
• Significant figures


  • Non-zero numbers are s.f.
  • Captive zeros in between non zeros numbers are s.f.
  • Leading zeros are not s.f.
  • Trailing zeros are s.f. if there is a decimal at the end, if there are no decimals then they are not
• Density


  • Mass/ volume
  • How heavy a substance is … Depending on: mass of particles and how tightly packed together the particles are
• Increasing temperature


  Particles separate, become less heavy, density decreases
• Solid


  • Rigid shape, fixed volume, tightly packed particles, behaviour is understood
• Liquid


  • Fluid shape, not fixed volume, behaviour isn't understood well, particles are further apart
• Gas


  • Expand to fill their space, behaviour very well understood, particles are very far apart
• Particles move closer together

  1. Energy released as heat

  2. Evaporation: liquid to gas

  3. Fusion (melting): solid to liquid

  4. Sublimation: solid to gas without having it become liquid first
• Particles move further apart

  1. Energy input required

  2. Condensation: gas to liquid

  3. Solidification (freezing): liquid to solid

  4. Deposition (frost): gas to solid
• Chemical element


  Pure substance that cannot be further broken down
• Physical properties


  • Colour
  • Odour
  • State of matter
  • Appearance
  • Melting, boiling point, sublimation ability
  • Solubility
  • Electrical conductivity
  • Malleability, ductility
  • Magnetic properties, viscosity, density
• Compounds


  Composed of 2 or more elements atoms/ ions in a fixed ratio
• Covalent/ molecular compounds


  • Atoms bonded together that don't contain a charge or metal
• Ionic compounds


  • Charged atoms or group of atoms
  • Containing a metal
• Potential energy


  Associated with position
• Types of potential energy

  • Gravitational energy: objects held at a height
  • Chemical energy: energy stored in molecules due to bonds between atoms
  • Electrostatic energy: due to attractions between charged particles
  • Nuclear energy: energy associated with attractions between nuclear particles
• Kinetic energy


  Associated with motion, strongly related to temperature
• Types of kinetic energy

  • Mechanical: movement of macroscopic objects
  • Thermal: motion at the particulate level
  • Electrical: movement of electrons in a conductor
  • Acoustic: compression-type wave motion
• Types of matter


  • Solid
  • Liquid
  • Gas
• Types of heterogeneous matter

  • Separation
  • Non-uniform
• Homogeneous matter


  Uniform in appearance, mixed properly
• Solution


  Uniform mixture of substances
• Pure substance


  Fixed composition, cannot be purified or broken down further
• Element


  Cannot be subdivided by chemical or physical needs
• Compound


  Cannot be subdivided by physical methods, needs to be chemical broken down
• Separating homogeneous mixtures


  1. Distillation: separating parts of a liquid by heating it up into vapour, and then condensing it back into a liquid

  2. Chromatography: determining how many components are in a mixture
• Physical change


  Change in organization of particles
• Chemical change


  Rearrangement of bonds between atoms and ions
• Atomic structure


  The arrangement of protons, neutrons, and electrons in an atom, as well as the energies associated with these particles
• Atomic structure


  • Can help explain various properties of an element, such as its chemical behavior and electron configuration