Chemistry

• The elements of the periodic table show trends across periods and down main groups, including in atomic radii, valencies, 1st ionisation energy, and electronegativity as exemplified by groups 1, 2, 13–18 and period 3
• Core charge values

  • Hydrogen: +1
  • Helium: +2
  • Lithium: +1
  • Sodium: +1
• The structure of the periodic table is based on the atomic number and the properties of the elements
• Core charge

  The sum charge of all subatomic particles excluding valence electrons. It is calculated as the number of protons minus the number of inner electrons. Protons attract valence electrons, while inner electron shells repel them, resulting in a constant core charge down the group
• Successive ionisation energies

  Harder to remove interior electrons, each new shell attacked requires more energy due to the fight to retain a full outer shell and increased core charge. Significant jumps occur due to sub shells and electron pairings
• Atomic radius

  Increases as the number of shells increases (period number increases). Core charge increase within each period or shell number results in a smaller atomic radius due to increased pull from the nucleus on valence electrons
• Electronegativity


  The tendency of an atom to attract a bonding pair of electrons. It increases with smaller atomic radius and more core charge, providing a stronger pull to accept electrons
• First ionisation energy

  The amount of energy required to remove the most loosely bound electron, the valence electron, of an isolated gaseous atom to form a cation. It increases with more core charge and smaller radius, making it difficult to remove electrons
• Compound


  Atoms of two or more different elements chemically bonded together
• Mixture


  Different elements or compounds together, but not chemically joined
• Molecule


  Two or more atoms joined together in a discrete unit, may be the same element or different
• Materials

  • Pure substances have distinct measurable properties, including melting and boiling points, reactivity, hardness, and density; mixtures have properties dependent on the identity and relative amounts of the substances that make up the mixture
• Element


  The simplest type of pure substance, containing only one type of atom
• Pure substances


  • May be elements or compounds consisting of atoms of two or more elements chemically combined; the formulae of compounds indicate the relative numbers of atoms of each element in the compound
• A mixture is two or more substances of different identity that are not chemically bonded
• Differences in physical properties of substances in a mixture

  • Including particle size, solubility, density, and boiling point, can be used to separate them
• Mixtures can be of elements, of molecules, or of compounds
• A mixture's properties can be changed based on the proportion of different components
• Homogeneous mixtures are the same throughout, while heterogeneous mixtures are different throughout
• Solutions


  Homogeneous mixtures of solvent and solute(s)
• Mixtures can be consistent throughout with equal proportions of components in any sample taken or have various states, colors, and compositions
• Evaporation and Distillation

  Evaporation is used to separate components with different boiling points by heating the mixture to reach the lower boiling point; distillation is used to retain both components by condensing and cooling the vapors
• Unsaturated solutions have enough solvent to dissolve more solute, saturated solutions have as much solute dissolved as possible, and supersaturated solutions have dissolved more solute than usually possible
• Separating Mixtures


  Mixtures, including solutions, can be separated into pure substances based on the different physical properties of the components
• Sieving and Filtering

  Both work using particle size; sieving is used to remove particles based on size, while filtering is used to separate substances based on size and solubility
• Evaporation


  If two substances in a solution have different boiling points, by slowly heating the mixture, you can reach the lower boiling point and remove one component as a gas
• Magnetic and Electrical Separation

  Iron, nickel, and cobalt can gain induced magnetism. A mixture of sand and iron filings can be separated by passing a magnet over the mixture. Electrophoresis is a technique to separate molecules based on electric charge
• Fractional Distillation


  In a sample with more than two parts or where the boiling points are very close, fractional distillation is used. The sample is heated and turned into a gas, fed into a fractional column. Hot gases rise, and the column gets cooler as it rises. Components with high boiling and condensation temperatures condense low in the column, while those with lower boiling/condensing points continue as a gas higher up in the colder region of the column
• Distillation

  If you wish to retain both components, use a condensation tube to capture and cool the vapor, returning it to liquid state and directing it into a receptacle
• Density is a measure of how much mass a substance has per unit volume. Denser materials sink, and less dense materials float
• Decanting and Centrifuges


  Density is a measure of how much mass a substance has per unit volume. Decanting involves pouring off the water from a settled mixture of sand and water. Centrifuge spins a sample rapidly to separate components based on density
• Separating funnels

  A separating funnel is used to separate liquids of different densities. The denser layer can be released in a slow and controlled manner using the tap, while the less dense layer remains in the separating funnel
• Atoms are everything that has mass and all matter is made of atoms
• Atoms combine to create compounds, mixtures, and molecules
• Atoms are not visible to the naked eye and have only been visualized using scanning electron microscopes
• Atoms were described as indivisible by Greek philosophers
• Key points about atoms from the Syllabus

  • Elements are represented by symbols
  • Atoms can be modelled as a nucleus, surrounded by electrons in distinct energy levels, held together by electrostatic forces of attraction between the nucleus and electrons; the location of electrons within atoms can be represented using electron configurations
• Electric current and static electricity result from electrons moving between atoms
• John Dalton formalized the concept of atoms in 1803
• John Dalton's details about atoms

  • All atoms of the same element are alike
  • Atoms of different elements are different
  • Chemical reactions occur when atoms are separated, joined, or rearranged
  • Atoms of one element never change into atoms of another element