atomic structure and the periodic table

• Element


  All of the atoms are the same
• Symbol


  Starts with a capital letter
• Compound


  Two or more different elements chemically combined in fixed proportions
• Compounds usually have totally different properties to the elements they are made from</b>
• Mixture


  Different elements or compounds, not chemically combined
• Mixture components

  • Magnesium atoms
  • Sulfur atoms
  • Magnesium sulfide
• Separation techniques for mixtures

  • Filtration
  • Distillation
  • Crystallization
  • Chromatography
• Molecule


  Any elements chemically combined, even if they are the same element
• Molecules


  • Methane
  • Water
  • Ammonia
  • Chlorine
  • Oxygen
• Molecules that are not compounds contain the same element
• Chemical formula


  Tells us the elements in a molecule and the numbers of atoms of each element
• In a specific compound, the number of atoms of each element is fixed and cannot be changed</b>
• Interpreting a chemical formula

  1. Identify the elements

  2. Determine the number of atoms of each element
• Brackets in a chemical formula indicate that the numbers inside the brackets apply to all the elements within
• Plum pudding model


  An atom is a ball of positive charge with negative electrons embedded in it
• Alpha scattering experiment


  1. Scientists took a piece of gold foil

  2. Fired tiny positive alpha particles at the gold foil

  3. Most alpha particles passed straight through the gold foil

  4. Some alpha particles were deflected

  5. Some alpha particles bounced straight back
• Most alpha particles went straight through the gold foil


  Atoms are mainly empty space
• Some alpha particles were deflected


  The center of the atom must have a positive charge
• Some alpha particles bounced straight back


  The center of the atom must contain a great deal of mass
• Nuclear model


  Most of the atom is empty space, with a tiny positive nucleus containing most of the mass, and negative electrons around the edge
• The nuclear model replaced the plum pudding model based on the results of the alpha scattering experiment
• Nuclear model of atomic structure

  Most of an atom is empty space, with a positive nucleus containing most of the mass, and negative electrons at the edge
• Nuclear model


  • Electrons orbit the nucleus at specific distances (energy levels/shells)
  • Positive charge in nucleus due to protons
  • Nucleus also contains neutral particles called neutrons
• Radius of an atom is around 0.1 nanometers
• Radius of the nucleus is approximately 1 * 10^-14 m
• Nearly all the mass of the atom is found in the nucleus
• Relative charge


  The charge of one particle compared to another particle
• Relative charge of particles

  • Protons: +1
  • Neutrons: 0
  • Electrons: -1
• Atoms have no overall charge because the number of electrons equals the number of protons
• Relative mass


  The mass of one particle compared to another particle
• Relative mass of particles

  • Protons: 1
  • Neutrons: 1
  • Electrons: much smaller than 1
• Atomic number


  Number of protons in atoms of an element
• Mass number


  Total number of protons and neutrons in atoms of an element
• Atoms have no overall charge because the number of electrons is the same as the number of protons
• Elements and their properties

  • Boron: 4 protons, 5 neutrons, 4 electrons
  • Sodium: 11 protons, 12 neutrons, 11 electrons
  • Fluorine: 9 protons, 10 neutrons, 9 electrons
  • Phosphorus: 15 protons, 16 neutrons, 15 electrons
• Isotopes


  Atoms of the same element with different numbers of neutrons
• Isotopes of carbon


  • 6 protons, 6 neutrons
  • 6 protons, 7 neutrons
  • 6 protons, 8 neutrons
• Isotopes of chlorine


  • 17 protons, 18 neutrons
  • 17 protons, 20 neutrons
• Ions


  Atoms which have an overall charge due to losing or gaining electrons
• Ions


  • Sodium ion: 11 protons, 12 neutrons, 10 electrons (1+ charge)
  • Fluoride ion: 9 protons, 10 neutrons, 10 electrons (1- charge)
  • Oxide ion: 8 protons, 8 neutrons, 10 electrons (2- charge)
  • Aluminium ion: 13 protons, 14 neutrons, 10 electrons (3+ charge)