Chemistry and Matter: Observations & Scientific Integrity

Chemistry and Matter

• Chemistry is the study of matter
• Matter occupies space and has mass
• Mass is the measure of the amount of matter in an object

Qualitative vs Quantitative Observations

• Qualitative observations do not involve numbers; they include color, appearance, and descriptions like "large" or "small"
• Qualitative observations include stating if something is hot or cold without specifying a temperature or identifying something by smell
• Quantitative observations specify measurable attributes or quantities
• Quantitative observations use numbers with units from measurements and dimensions like mass, time, distance, volume, density, or temperature and color which is specified as a wavelength

Goals and Integrity in Science

• Science aims for prediction, control, understanding, and explaining phenomena
• Experimental results should be reproducible and reported in detail for others to use or reproduce
• Conclusions should be reasonable and unbiased, and credit must be given where it is due

Classification of Matter

• Matter can be classified by its physical state as gas, liquid, or solid
• Matter can be classified by its composition: element, compound, or mixture

States of Matter

• Solids have a definite shape and volume with the lowest kinetic energy
• Liquids have an indefinite shape, a definite volume, and intermediate kinetic energy
• Gases have an indefinite shape and volume with the highest kinetic energy

Homogeneous vs. Heterogeneous Mixtures

• Homogeneous mixtures consist of two or more substances in the same phase, with uniform properties throughout
• Heterogeneous mixtures do not have uniform composition, and their components are visually distinguishable
• Separation of both homogeneous and heterogeneous mixtures results in pure substances

Separating Mixtures by Physical Properties

• Filtration is a means of separation for a state of matter of mixtures and solubility of mixtures
• Magnetism separates mixtures
• Chromatography separates intermolecular forces of mixtures
• Density can be separated by decantation and/or centrifugation
• Distillation separates mixtures because of boiling point
• Vapor pressure results in the separation of mixtures by Evaporation

Pure Substances: Elements and Compounds

• Pure substances have well-defined physical and chemical properties that can be classified as elements or compounds
• Elements consist of one type of atom that cannot be decomposed or simplified by ordinary means
• Compounds can be reduced into two or more elements
• Sodium and Helium are examples of elements.
• Water, or H2O, is an example of a compound

Elements on the Periodic Table

• Elements are recorded on the Periodic Table; there are 118 recorded elements

Chemical Compounds

• Chemical compounds are composed of two or more atoms
• Compounds are made up of molecules or ions
• A molecule is the smallest compound unit that retains its chemical characteristics
• Ionic compounds are described by a "formula unit."
• Molecules are described by a "molecular formula."
• Water's molecular formula is H2O, Methane's is CH4, Ammonia's is NH3, and Carbon Dioxide's is CO2

Physical Properties

• Physical properties can be evaluated without changing the material's composition:
  • Color
  • Odor
  • Density
  • Melting point
  • Thermal conductivity
  • Volume
  • Hardness
• Physical properties include color, state (solid, gas, or liquid), melting and boiling point, and density (mass/unit volume)
• Extensive properties like mass depend upon the amount of substance
• Intensive properties like density do not
• Physical properties are affected by temperature (molecular motion)

Chemical Properties

• Chemical properties result in a change in the composition of a material and explain how one substance acts with another
• A chemical reaction describes how the change occurs
• Combustion is a chemical property of wood in its ability to burn
• Chemical properties are really chemical changes
• Chemical properties of elements and compounds are related to periodic trends and molecular structure

Atoms and Molecules

• Models help to visualize atoms and molecules
• An atom is the smallest element unit with all the element's properties
• A molecule is the smallest pure substance unit with all that substance's properties and may contain more than one atom and element

Physical vs Chemical Changes

• Physical changes do not change chemical composition; for example, Solid iron (Fe) melts when heated to become Fe(l) and Ice becomes H2O(1) when melting
• Chemical changes involve a change in chemical composition and structure; for example, Iron metal reacts with oxygen to form rust: 4Fe + 3O2 → 2 Fe2O3 and H2 and O2 react to form Water: 2H2 + O2 → 2H₂O
• Chromatography separates mixture components without changing them, representing a physical change
• Electrolysis changes water into hydrogen and oxygen, representing a chemical change

Energy

• Classified as Kinetic or Potential
• Kinetic energy relates to motion, such as:
  • Motion at a particulate (thermal energy) and macroscopic level (thrown baseball and falling water)
  • The movement of electrons in a conductor (electrical energy)
  • Wave motion (transverse water and compression acoustic)
• Potential energy results from an object's position, such as:
  • Gravitational: An object held; waterfalls
  • Energy stored in an extended spring and in molecules (chemical energy, food)
  • The energy related to charged or partially charged particles (electrostatic energy)
  • Nuclear energy (fission or fusion)