solids, liquids, gases

• Learning science is the study of how people learn and the application of scientific principles to improve educational practices.
• Solids have a fixed volume and shape
• Liquids have a fixed volume but no definite shape, taking on the shape of their container
• Gases have no fixed volume or shape, spreading out to fill whatever container or space they are in
• To change solids into liquids and then into gases, heat energy must be put in to provide the particles with enough energy to overcome the forces holding them together
• The temperature at which one state changes to another have specific names:

  • Melting point: solid to liquid
  • Boiling point: liquid to gas
  • Freezing point: liquid to solid
  • Condensation point: gas to liquid
• Elements are substances made up of one kind of the same small particle called atoms, which are combined with other atoms to form molecules
• A solution is formed when a solute (solid) dissolves in a solvent (liquid), with the more solute that dissolves, the more concentrated the solution becomes
• Purifying impure solids involves adding a solvent that the required solid is soluble in, filtering the mixture to remove insoluble impurity, heating the solution to remove some solvent, leaving it to crystallize, filtering off crystals, washing with a small amount of cold solvent, and drying them to obtain a pure solid
• Purifying impure liquids can be done through distillation for liquids contaminated with soluble solids dissolved in them, or fractional distillation for liquids contaminated with other liquids, which uses the difference in boiling points of different liquids mixed together
• In a chemical change, one or more new substances are produced, often with an observable change, a change in mass (which is conserved in all chemical reactions), and an energy change
• All matter can be classified into elements, mixtures, and compounds, with elements ordered in the Periodic Table and most elements classified as metals or non-metals
• Metals have properties like being good conductors of electricity, having high melting points, being good conductors of heat, sonorous, ductile, malleable, and shiny, with exceptions like alkali metals having low melting points and not being sonorous, and mercury having a low melting point
• Typical properties of non-metals include low melting points, being poor conductors of heat and electricity, brittle, and dull
• Exceptions to typical non-metal properties:

  • Carbon in the form of graphite is a good conductor of electricity
  • Carbon and silicon have high melting points
• In 1808, John Dalton published a book outlining his atomic theory:

  • All matter is made of small, indivisible spheres called atoms
  • All atoms of a given element are identical and have the same mass
  • Atoms of different elements have different masses
  • Chemical compounds are formed when different atoms join together
  • All molecules of a chemical compound have the same type and number of atoms
• Dalton's atomic theory has evolved, with modern theory focusing on sub-atomic particles like protons, neutrons, and electrons
• Sub-atomic particles:

  • Proton: Relative mass 1, Relative charge +1
  • Neutron: Relative mass 1, Relative charge 0
  • Electron: Relative mass (1/2000), Relative charge -1
• Protons and neutrons are found in the nucleus of an atom, while electrons form shells around the nucleus
• Arrangement of electrons in an atom:

  • Electrons are arranged in shells around the nucleus
  • The shell nearest to the nucleus can hold 2 electrons, while the next shell can hold 8 electrons
• Solids have a fixed volume and shape, are not easily compressed, and do not flow easily
• Liquids assume the shape of the container they occupy, are not easily compressed, and flow easily
• Gases assume the shape and volume of their container, are compressible, and flow easily
• Evaporation is when particles break away from the surface of a liquid and form a vapor, causing cooling as the more energetic molecules escape from the surface