topic 1- atomic structure and periodic table

• All substances are made of atoms- They're really finy-foo small to see, even with your microscope
• A 50p piece contains about 77400 000 000 000 000 000 000 of atoms
• Components of atoms


  • Protons
  • Neutrons
  • Electrons
• Atom radius


  About 9.1 nanometres
• Nucleus


  • In the middle of the atom
  • Contains protons and neutrons
  • Radius of around 1 nanometre
  • Has a positive charge because of the protons
  • Almost the whole mass of the atom is concentrated in the nucleus
• Protons


  Heavy and positively charged
• Neutrons


  Heavy and neutral
• Electrons


  Tiny and negatively charged
• Electron mass is often taken as the reference for relative mass
• Electrons


  • Move around the nucleus in electron shells
  • Negatively charged and tiny, but they cover a lot of space
  • The volume of their orbits determines the size of the atom
  • Have virtually no mass
• Number of protons equals number of electrons in atoms
• Atoms are neutral - they have no charge overall
• In an ion, the number of protons doesn't equal the number of electrons, so it has an overall charge
• Atomic number


  Tells you how many protons there are
• Mass number


  Tells you the total number of protons and neutrons in the atom
• To get the number of neutrons, subtract the atomic number from the mass number
• Elements are substances made up of atoms that all have the same number of protons in their nucleus
• Atoms can have different numbers of protons, neutrons and electrons
• It's the number of protons in the nucleus that decides what type of atom it is
• There are about 100 different elements
• Atomic symbols


  One or two letter symbols that represent atoms of each element
• Isotopes


  • Different forms of the same element, which have the same number of protons but a different number of neutrons
  • Have the same atomic number but different mass numbers
• Relative atomic mass


  An average mass taking into account the different masses and abundances of all the isotopes that make up the element
• Compounds are substances formed from two or more elements, the atoms of each are in fixed proportions throughout the compound and they're held together by chemical bonds
• Chemical bonds


  Involve atoms giving away, taking or sharing electrons - the nuclei of the atoms aren't affected
• Ionic compounds


  • Formed from a metal and a non-metal, consist of ions where the metal atoms lose electrons to form positive ions and the non-metal atoms gain electrons to form negative ions
• Covalent compounds


  • Formed from non-metals, consist of molecules where each atom shares an electron with another atom
• The properties of a compound are usually totally different from the properties of the original elements
• Chemical formula


  Represents a compound using elemental symbols in the same proportions as in the compound
• Chemical equations are used to show chemical reactions
• Reactants


  The molecules on the left-hand side of a chemical equation
• Products


  The molecules on the right-hand side of a chemical equation
• Chemical equations must be balanced - there must always be the same number of atoms on both sides
• Mixtures are easily separated, unlike compounds
• The properties of a mixture are just a mixture of the properties of the separate parts
• Paper chromatography


  1. Draw a line near the bottom of filter paper

  2. Add a spot of the mixture

  3. Place the paper in a solvent

  4. Solvent seeps up the paper, carrying the mixture with it

  5. Different components separate out and form spots at different heights
• Filtration


  Used to separate insoluble solids from liquids
• Evaporation


  1. Pour the solution into an evaporating dish

  2. Slowly heat the solution until crystals form

  3. Keep heating until all the solvent has evaporated and only dry crystals remain
• Crystallisation


  1. Pour the solution into an evaporating dish

  2. Slowly evaporate the solvent until crystals form
• Insoluble


  The solid can't be dissolved in the liquid