chemistry GCSE

• This is good for higher and Foundation Tier double combined Trilogy and triple separate chemistry that's topics 1 to five atoms bonding quantitative chemistry and chemical and energy changes
• Substances are made of atoms
• Element


  Different types of atoms represented in the periodic table by a symbol
• Compound


  Substance that contains two or more different types of atoms chemically bonded together
• If there's no number after a symbol, there's an invisible 1
• Chemical reactions

  Atoms change what they're bonded to and how they're bonded
• Word equation


  Representation of a reaction using words
• Chemical equation


  Representation of a reaction using symbols
• Atoms are not created or destroyed in any chemical reaction, so the same number of each type of atom must be on both sides of the equation</b>
• Balancing chemical equations


  Start with atoms only in compounds, then balance remaining atoms by putting numbers in front of elements/compounds
• Mixture


  Any combination of different types of elements and compounds that aren't chemically bonded together
• Solution


  Mixture of a solute (solid dissolved in a liquid) and a solvent
• Separation techniques


  1. Filtration

  2. Crystallization

  3. Distillation
• Physical processes


  • No new substances are being made
• States of matter


  • Solid (particles vibrate around fixed positions)
  • Liquid (particles free to move past each other)
  • Gas (particles far apart and move randomly)
• Gases can be compressed, solids and liquids cannot
• Melting and evaporation


  Require energy (usually heat) to overcome electrostatic forces of attraction between particles
• Melting and evaporation are physical changes, not chemical reactions
• Atomic models


  • JJ Thompson's plum pudding model
  • Rutherford's discovery of the nucleus and mostly empty space
  • Bohr's discovery of electron shells/orbitals
  • Chadwick's discovery of neutrons
• Protons


  Positive charges in the nucleus
• Electrons


  Negative charges orbiting the nucleus
• Neutrons


  Neutral charges in the nucleus
• Atomic number


  Number of protons in the nucleus
• Mass number


  Number of protons and neutrons in the nucleus
• Isotopes


  Atoms of the same element with different numbers of neutrons
• Relative abundance


  Percentage of each isotope in a sample
• Periodic table


  Organises elements by their properties
• Development of the periodic table

  1. Ordered by atomic weight

  2. Grouped by properties (Mendeleev)
• Electron configuration


  Arrangement of electrons in shells/orbitals around the nucleus
• Sections of the periodic table

  • Metals (left of staircase)
  • Non-metals (right of staircase)
  • Transition metals
• Group


  Column in the periodic table, indicates number of outer shell electrons
• Groups


  • Group 1 (alkali metals)
  • Group 7 (halogens)
  • Group 0 (noble gases)
• Alkali metals


  • Have one outer electron which they readily donate
  • Reactivity increases down the group
• Halogens


  • Have seven outer electrons and readily accept one more
  • Reactivity decreases down the group
  • Boiling points increase down the group
• Noble gases


  • Have full outer shells, are very unreactive
• Ion


  Atom that has gained or lost electrons, no longer electrically neutral
• Ionic bonding


  • Metal atoms donate electrons to non-metal atoms to form ions
  • Ionic compounds have high melting/boiling points and can conduct electricity when molten or in solution
• Molecular ion


  Ion formed from a molecule, e.g. hydroxide ion (OH-)
• Salt


  Any ionic compound, not just sodium chloride
• Covalent bonding


  • Non-metal atoms share electrons to fill their outer shells
  • Forms simple molecular or giant covalent structures
  • Simple molecular structures have low melting/boiling points and cannot conduct electricity