chemistry paper 1

• Substances are made of atoms, the different types of atoms are represented in the periodic table by a symbol
• Compound


  A substance that contains two or more different types of atoms chemically bonded together
• For every one oxygen atom there are two hydrogen atoms
• If there's no number after a symbol, there's an invisible one
• Chemical reactions


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


  A way to represent a chemical reaction
• Chemical equation


  A way to represent a chemical reaction using symbols
• Atoms are not created or destroyed in any chemical reaction, there must be the same number of each type of atom on both sides
• Balancing chemical equations


  Start with atoms that are only in compounds, then balance other atoms by putting numbers in front of elements or compounds to multiply them up
• Mixture


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


  A mixture of a solute (solid dissolved in a liquid) and a solvent
• Separating mixtures


  1. Filtration (for large insoluble particles)

  2. Crystallization (to leave a solute behind after evaporating the solvent)

  3. Distillation (to separate liquids with different boiling points)
• These are all physical processes, not chemical reactions, as no new substances are being made
• States of matter


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


  Require supplying energy, usually in the form of heat, to overcome the electrostatic forces of attraction between the particles
• Melting and evaporation are physical changes, not chemical reactions, as no chemical bonds are broken
• Atom


  • Made up of positive and negative charges (discovered by JJ Thompson)
  • Positive charge is in a small nucleus, with electrons orbiting relatively far away (discovered by Ernest Rutherford)
  • Electrons exist in shells or orbitals (discovered by Niels Bohr)
  • Nucleus contains protons (positive charges) and neutrons (neutral charges) (discovered by James Chadwick)
• Proton


  Positive charge, relative mass of 1
• Electron


  Negative charge, very small mass compared to protons and neutrons
• Neutron


  Neutral charge, relative mass of 1
• Atomic number


  Number of protons in the nucleus, determines the element
• Mass number


  Total number of protons and neutrons in the nucleus
• Isotopes


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


  The percentage of each isotope of an element found naturally
• The periodic table was originally ordered by atomic weight, then later grouped by properties (discovered by Dmitri Mendeleev)
• Electron configuration


  The arrangement of electrons in an atom's shells or orbitals
• Sections of the periodic table

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


  The column an atom is in, indicates the number of electrons in the outer shell
• Group 1 (alkali metals)


  • Have one electron in their outer shell, which they readily donate
  • Reactivity increases down the group as the outer electron is further from the nucleus
• Group 7 (halogens)


  • Have seven electrons in their outer shell, need one more to be full
  • Reactivity decreases down the group as the outer electron is further from the nucleus
• Group 0 (noble gases)

  • Have a full or empty outer shell, so are very unreactive
• Ion


  An atom that has gained or lost electrons, so is no longer neutral
• Transition metals


  • Can form ions with different charges depending on how many electrons they donate
• Metallic bonding


  Atoms in a metal are bonded together in a lattice, with delocalized electrons around them
• Metallic properties


  • Good conductors of electricity and heat
  • Malleable and ductile
• Ionic bonding


  A metal atom donates electrons to a non-metal atom, forming positive and negative ions that are attracted to each other
• Forming ionic compounds


  1. The charges of all ions must add up to zero

  2. Consist of a lattice of repeating units of the ions
• Ionic compounds


  • Have high melting and boiling points
  • Can conduct electricity when molten or in solution
• Covalent bonding


  Non-metal atoms share electrons to fill their outer shells