Atomic Structure + the Periodic Table

• Atoms are neutral, so they have equal numbers of electrons and protons.
• The number of protons determines the element
• Atoms have a radius of around 0.1 nanometres
• The nucleus has an overall positive charge
• Electrons have a negative charge
• Protons have a positive charge
• Isotopes are atoms with different numbers of neutrons but the same number of protons
• The relative mass of a proton or neutron is 1
• The relative mass of an electron is very small (around 1/2000 and often taken as zero)
• Mass number = sum of protons and neutrons
• Atomic number = number of protons
• Ar = relative atomic mass
• Ar = sum of (isotope abundance x isotope mass number)/

  sum of abundances of all the isotopes
• Compounds are substances that are made up of two or more elements chemically combined.
• Compounds are in fixed proportions and held together by chemical bonds.
• Ammonia = NH3
• Sodium chloride = NaCl
• Hydrochloric acid = HCl
• Calcium chloride = CaCl2
• Sodium carbonate = Na2CO3
• Sulphuric acid = H2SO4
• In mixtures there are no chemical bonds between atoms
• Separation techniques

  • Chromatography
  • Filtration
  • Crystallisation
  • Distillation
• JJ Thompson came up with the 'plum pudding' model of the atom.
• John Dalton was the first to propose that all matter is made up of tiny spheres called atoms.
• Ernest Rutherford conducted the alpha particle scattering experiment in 1909
• The alpha particle experiment showed that most of an atom's mass was concentrated in the centre.
• Niels Bohr proposed that electrons orbited the nucleus in shells
• James Chadwick discovered the neutron.
• There are two electrons in the shell closest to the nucleus
• Each electron shell (except the first) can hold 8 electrons.
• Mendeleev developed the modern periodic table in 1869
• Mendeleev ordered the elements in order of atomic mass and the properties of the element
• Metals can be found on the left side of the periodic table
• Non-metals can be found on the right side of the periodic table
• The vertical columns of the periodic table are groups. The horizontal rows are periods.
• The group number of an element tells you how many electrons it has in its outer shell. Elements in a group all have similar properties.
• Metals react to form positive ions and non-metals react to form negative ions.
• The properties of metals are:

  • strong but malleable
  • good conductors of heat and electricity
  • high melting and boiling points
  • usually shiny
  • ductile
• The properties of non-metals are:

  • dull looking
  • brittle
  • not always solids at room temp
  • don't conduct electricity
  • lower density