chemistry

• Element


  Contains only one type of atom
• Compound


  Substance made from two or more different elements chemically joined (i.e. bonded) together
• Mixture


  Substance made of two or more different elements and/or compounds not chemically joined together
• Models of the atom developed by scientists

  • John Dalton (early 1800s)
  • Ernest Rutherford (1909)
  • J.J. Thompson (late 1800s)
  • Niels Bohr (1914)
  • James Chadwick (1932)
• Rutherford's Gold Foil Experiment

  1. Positively charged alpha particles shot at gold foil

  2. Expected to go straight through

  3. Actually scattered (bounced in lots of different directions)
• Rutherford's nuclear model


  Positive charge (protons) concentrated in a central part of the atom, its nucleus

  
• Thompson's 'plum pudding' model

  Tiny negatively charged electrons embedded in a cloud of positive charge
• Bohr's model


  Electrons orbit the nucleus at set distances (i.e. energy levels)

  
• All substances are made up of atoms – the smallest indivisible particles that make up matter
• Atoms are made of protons, neutrons and electrons

  
• Protons and neutrons are found in the nucleus (the centre of the atom)

  
• Atomic number


  Number of protons in an atom
• Mass number


  Number of protons + neutrons in an atom
• Number of electrons = number of protons
• Electrons


  Found in energy levels (i.e. shells) around the nucleus, with the lowest energy level filled first
• Subatomic particles


  • Proton (+1 charge, 1 relative mass)
  • Neutron (0 charge, 1 relative mass)
  • Electron (-1 charge, negligible relative mass)

  
• Atoms have no charge because they contain the same number of protons and electrons
• Isotopes


  Atoms with the same number of protons (atomic number) but different numbers of neutrons (mass number)
• Ions


  • Charged particles
  • Negative ions formed when electrons are gained
  • Positive ions formed when electrons are lost
• The periodic table arranges the elements by atomic (proton) number
• Elements with similar properties are in the same column (group) and have the same number of electrons in their outside shell

  
• Periodic table


  So called because of the regularly repeating patterns in the properties of the elements
• Newlands introduced 'law of octaves' when he noticed that the properties of every eighth element seemed similar, but his pattern broke down after calcium
• Mendeleev ordered elements by atomic number and their properties, leaving gaps for unknown elements which when discovered matched his predictions
• Arrangement of elements in the periodic table

  • Metals on the left and bottom
  • Non-metals on the right and top
• Metals


  Tend to lose electrons, forming positive ions
• Non-metals


  Tend to gain electrons, forming negative ions
• Noble gases (Group 0)

  Unreactive because of their very stable electron arrangements (full outer shell)
• Properties of Group 1 alkali metals

  • Melting/boiling point decrease down the group
  • React with water to produce a metal hydroxide solution (an alkali) and hydrogen gas
  • Reaction gets more violent down the group
• As you go down Group 1, the elements get more reactive because there are more shells of electrons, the outer electron is further from the positive nucleus, the attraction between electron and nucleus is weaker, and the electron is lost more easily