chemistry

• Atoms are the base building blocks of ordinary matter
• Atoms can join together to form molecules, which form most the objects around you
• Atom


  Composed of particles called electrons, protons, and neutrons
• The periodic table has elements numbered 1 through 7 on the left hand side
• Elements that are in the same period have properties that are not as similar
• Element


  A substance made from only one type of atom
• Compound


  A molecule made of atoms from different elements
• Mixture


  Contains two or more substances that have not reacted chemically with each other
• Plum Pudding Model


  • Proposed by J. Thomson in the late 19th century
  • Atoms are composite objects, made of pieces with positive and negative charge
  • Negatively charged electrons within the atom are very small compared to the entire atom
• Atomic Theory


  1. Niels Bohr adapted Ernest Rutherford's nuclear model

  2. Electrons orbit the nucleus in shells

  3. Nucleus contains protons and neutrons
• Discovery of the nucleus

  • In 1909 Ernest Rutherford designed an experiment to test the plum pudding model
  • Most alpha particles went straight through the gold foil, but a few were scattered in different directions
  • This led Rutherford to suggest a new model for the atom, called the nuclear model
• Electrons


  Occupy the lowest available energy levels, also called electron shells, outside the nucleus
• Mendeleev left gaps in his periodic table for elements not known at the time
• Mendeleev was able to predict the properties of these undiscovered elements by looking at the properties of the elements next to the gaps
• Laboratory equipment

  • Thermometer
  • Condenser
  • Flask
  • Beaker
  • Bunsen Burner
• Group 0 elements (noble gases)

  • Show trends in their physical properties
  • Their uses depend on their inertness, low density and non-flammability
• Group 1 elements (alkali metals)


  • React vigorously with water to produce an alkaline solution
• Group 7 elements (halogens)


  • Form salts when they react with metals
• Properties of a typical metal (when solid)

  • Good conductor of electricity
  • Good conductor of heat
  • Shiny
  • High density
  • Malleable
  • Ductile
• Properties of a typical non-metal (when solid)

  • Poor conductor of electricity
  • Poor conductor of heat
  • Dull
  • Low density
  • Brittle
  • Brittle
• Formation of positive and negative ions


  1. Metal reacts with a non-metal

  2. Electrons are transferred
• Oppositely charged ions

  Strongly attracted to each other, forming ionic bonds
• Dot and cross diagram

  1. Models the transfer of electrons from metal atoms to non-metal atoms

  2. Electrons from one atom are shown as dots

  3. Electrons from the other atom are shown as crosses
• Covalent bond


  Formed when two atoms share a pair of electrons
• Covalent bonding

  • Occurs in most non-metal elements
  • Occurs in compounds formed between non-metals
• Shared electrons


  • Found in the outer shells of the atoms
  • Usually each atom contributes one electron to the shared pair
• Simple covalent molecules

  • Hydrogen
  • Ammonia
  • Methane
  • Water
• Simple covalent molecules


  • Have very strong bonds between the atoms
  • Have much weaker forces holding the molecules together
• Melting and boiling of simple covalent molecules

  Weak intermolecular forces break, not the strong covalent bonds
• Giant covalent structures


  • Very high melting points
  • Variable conductivity (diamond does not conduct, graphite does)
• Substances with giant covalent structures

  • Diamond
  • Graphite
  • Fullerene
• Diamond


  Each carbon atom is joined to four other carbon atoms by covalent bonds, forming a giant covalent structure
• Graphite


  Contains layers of hexagonal rings of covalently bonded carbon atoms, with weak forces between the layers
• Fullerene


  Consists of a hollow cage of carbon atoms with a regular structure
• Ionic compound


  A giant structure of ions, with a regular, repeating arrangement called a lattice
• Ionic compounds


  • Have high melting points
  • Form crystals
  • Do not conduct electricity
• Ions in ionic compounds

  • Na+
  • Mg2+
  • O2-
  • Cl-
• Metallic bonding


  Atoms arranged in a regular pattern, with delocalised electrons free to move through the whole structure
• Metals


  • Good conductors of electricity
  • Good conductors of thermal energy
  • Have high melting and boiling points
• In a pure metal, the force needed to make the layers slide over each other is small