Chemistry Module 1

• Matter


  Occupies space and possesses mass, and may exist as a solid, liquid, or gas
• Pure substance


  Matter having an invariant chemical composition and distinct properties
• Mixture


  Matter consisting of two or more pure substances that retain their individual identities and can be separated by physical methods
• Element


  A fundamental substance that cannot be separated into different substances by chemical methods
• Homogeneous


  A mixture having a uniform composition and properties throughout (also called a solution)
• Compound


  A substance composed of two or more elements in fixed proportions, and can be separated into simpler substances and elements only by chemical methods
• Heterogeneous


  A mixture not uniform in composition and properties throughout
• Physical and chemical properties


  • Physical properties: can be measured without changing the chemical composition of matter
  • Chemical properties need to be measured when a chemical reaction is occurring
• Filtration


  1. Separates insoluble substances in a mixture (such as solids from liquids)

  2. The liquid that passes through the filter is the filtrate, and the solid is the residue

  3. Filter paper has small pores larger chemicals cannot pass through

  
• Evaporation to Dryness and Crystallisation

  1. Insoluble components of a mixture are removed by filtration before evaporation is performed

  2. The solute has a higher boiling point than the solvent

  3. The solute evaporates (due to the lower boiling point) and the solvent crystallises
• Sedimentation and Decanting


  1. Separates insoluble solids from liquids

  2. Sedimentation causes the more dense particles to settle to the bottom and collect over time

  3. Decanting allows substances to be separated once sediment layers have formed

  
• Centrifugation


  1. Spins the mixture to separate the different substances

  2. Uses centrifugal force to separate substances by density

  3. The highest-density substance will be at the bottom

  
• Distillation


  1. Uses evaporation and condensation to extract a liquid from an impure mixture

  2. Two liquids can be separated if they have sufficiently different boiling points

  3. The liquid collected in distillation is known as the distillate

  
• Fractional Distillation


  1. A specialist version of distillation used to separate a mixture of substances with fairly close boiling points

  2. A fractioning column allows the mixture to be put through many successive distillations, resulting in many separate distillate
• Separating Funnel


  1. Two liquids that cannot be mixed are called immiscible

  2. Over time, a heterogenous mixture of immiscible substances will form layers with dense layers at the bottom

  3. A separating funnel can be used to pour each layer into a separate beaker

  
• Sieving


  1. Used to separate a mixture containing different-sized particles

  2. The Mesh of a sieve can be of different sizes to help eliminate the desired part of the mixture

  
• Froth Flotation


  1. A process that selectively separates hydrophobic (water avoiding) and hydrophilic (water mixing) properties

  2. Hydrophobic particles with the air bubbles attached are carried to the surface, thereby forming a froth that can be removed

  3. Hydrophilic materials stay in the liquid phase

  
• Percentage composition


  Determined by the mass of the component and the mass of the substance: % mass = mass of component in sample (g) / total mass of sample (g) x 100%
• Bohr model


  • Electrons travel in orbit around the atom
  • Electrons' orbits correspond to specific energy levels in the atom
  • Electrons can only occupy fixed energy levels and cannot exist between two energy levels
  • Orbits of larger radii correspond to higher energy levels
  • Innermost shell: lowest energy level
  • Outermost shell: highest energy level
• Flame tests


  Conducted to show the energy levels and sublevels of electrons in atoms
• Hydrogen emission spectrum


  The only one that aligned with Bohr's theory
• Electrons


  Move between energy levels by absorbing and emitting energy in the form of light
• Energy levels


  Quantised, meaning there can be one level or another but nothing in between
• Bohr's model could not accurately predict the emission spectra of atoms with more than one electron
• Bohr's model could not explain why electron shells can only hold 2n^2
• Bohr's model could not explain why the fourth shell accepts two electrons before the third shell is full
• Schrodinger's model


  • Electrons behave as particles and waves
  • Electrons behave as waves to occupy 3D space
  • Mathematical functions predicted the probability of finding electrons in these orbitals / electron clouds
• Major energy levels in an atom


  Called shells
• Shells


  Contain separate energy levels of similar energy called subshells, labelled s d p f
• Subshells


  Each can only hold a certain number of electrons
• Schrodinger's mathematical functions explained the emission spectra where Bohr's model could not
• Isotopes


  • Same number of protons, different numbers of neutrons
  • Named by mass numbers
• Radioisotopes


  • Spontaneously and continuously emit characteristic types of radiation
  • They do this to form stable nuclei
• Stable isotope


  • For atomic numbers 1-20, a neutron to proton ratio of about 1:1
  • For atomic numbers 20-50, the neutron to proton ratio for a stable nucleus is 1:5
• Unstable isotope


  • A nucleus whose neutron to proton ratio is too high or too low (compared to the value given by the zone of stability) will undergo a nuclear reaction in order to restore the ratio, and the element is said to be radioactive
  • Any nucleus with more than 83 protons is unstable because the force which holds the nucleons together is not strong enough
  • Large nuclei usually emit an alpha particle to reduce the number of protons and neutrons
• Alpha radiation


  • Helium nuclei
  • 2 charge
  • Stopped by paper and skin
  • Most dangerous when ingested as particles cannot penetrate the skin to escape
  • Travels 5% of the speed of light
  • Deflected by electric and magnetic fields as the nucleus is positively charged
• Beta particles


  • Also known as beta minus decay
  • High speed electron
  • A result of [neutron → proton + electron]
  • 1 charge
  • Travels around 100cm through air
  • Stopped by 5mm aluminium
  • Travels at 99% of the speed of light
  • Deflected by electron and magnetic fields
• Gamma rays


  • Electromagnetic radiation
  • No mass or charge
  • Stopped by several cm of lead or 1m concrete
  • Travels at the speed of light
  • Unaffected by electric and magnetic fields
  • Accompanies most types of decay
• Electron capture


  Occurs when an inner orbital electron is captured by the nucleus
• Positron emission


  • Also known as beta positive decay
  • A positron is a positively charged electron
  • When a proton → neutron, a positron is emitted