Paper1 GCSE

• 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 reaction


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


  Representation of a chemical reaction using words
• Chemical equation


  Representation of a chemical 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 or compounds
• Solution


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


  1. Filtration (separate large insoluble particles from a liquid)

  2. Crystallization (evaporate solvent to leave behind solute)

  3. Distillation (separate liquids based on different boiling points)
• Physical change


  Change in state of matter (solid, liquid, gas) without forming new substances
• Melting and evaporation require energy (usually heat) to overcome intermolecular forces
• Physical changes do not involve breaking or forming chemical bonds
• State symbols


  s for solid, l for liquid, g for gas, aq for aqueous (dissolved in water)
• Atom 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
• Proton


  Positive charge in the nucleus
• Electron


  Negative charge orbiting the nucleus
• Neutron


  Neutral charge in the nucleus
• Atomic number


  Number of protons in the nucleus
• Mass number


  Total 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


  Organizes elements based on their properties
• Development of the periodic table

  1. Ordered by atomic weight

  2. Grouped by similar properties (Mendeleev)

  3. Gaps predicted and later filled
• Electron configuration


  Arrangement of electrons in shells/orbitals around the nucleus
• Periodic table sections


  • Metals (left of staircase)
  • Nonmetals (right of staircase)
  • Transition metals
• Group


  Column in the periodic table indicating number of outer shell electrons
• Group names


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


  • Have 1 electron in outer shell, readily donate it
  • Reactivity increases down the group
• Halogens


  • Have 7 electrons in outer shell, readily accept 1 more
  • Reactivity decreases down the group
  • Boiling points increase down the group
• Noble gases


  • Have full or empty outer shells, very unreactive
• Ion


  Atom that has gained or lost electrons, no longer neutral
• Ion charges


  • Group 1 (1+)
  • Group 2 (2+)
  • Group 7 (1-)
  • Group 6 (2-)
  • Transition metals (variable)
• Metallic bonding


  • Metal atoms form a lattice with delocalized electrons, good conductors
• Ionic bonding


  • Metal atoms donate electrons to nonmetal atoms, forming a lattice of ions
  • Ionic compounds have high melting/boiling points, can conduct electricity when molten or in solution
• Covalent bonding


  Nonmetal atoms share electrons to fill outer shells, form discrete molecules
• Covalent compounds


  • H2, O2, N2, CH4, CO2
• Giant covalent structures


  • Atoms form an extended network of covalent bonds, very high melting/boiling points (e.g. diamond, graphite)
• Relative formula mass


  Sum of relative atomic masses of atoms in a compound