chem

• Elements contain only one type of atom
• Compounds


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


  Substances that are made of two or more different elements and/or compounds not chemically joined together
• Types of substances


  • Element
  • Compound
  • Mixture
• John Dalton


  • Used experiments to suggest substances were made up of tiny spheres called atoms, which could not be divided
• Ernest Rutherford


  • Based his suggestions on the Gold Foil / Alpha particle Experiment conducted by Geiger and Marsden
  • Suggested that the positive charge (protons) are found concentrated in a central part of the atom, its nucleus

  
• J.J. Thompson


  • Suggested the 'plum pudding' model– tiny negatively charged electrons embedded in a cloud of positive charge
• Niels Bohr


  • Suggested electrons orbit the nucleus at set distances (i.e. energy levels)

  
• James Chadwick


  • Discovered the neutron. This supported Rutherford's proposal
• 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


  The number of protons in an atom
• Mass number


  The number of protons plus neutrons in an atom
• Atomic mass = number of protons + number of neutrons
• Number of electrons = number of protons
• Energy levels (shells)


  The levels at which electrons are found around the nucleus

  
• Subatomic particles


  • Proton
  • Neutron
  • Electron
• Isotopes


  Atoms that have the same number of protons (ie. atomic number), but a different number of neutrons (i.e. mass number)
• Ions


  • Charged particles
  • Negative ions are formed when electrons are gained
  • Positive ions are formed when electrons are lost
• Periodic table


  • Arranges the elements by atomic (proton) number
  • Elements with similar properties are in the same column known as a group and have the same number of electrons in their outside shell
  • The Periodic Table is so called because of the regularly repeating patterns in the properties of the elements
• John Dalton, John Newlands, Dimitri Mendeleev


  • Suggested ordering elements by atomic weight, which led to incomplete versions or placed elements in inappropriate groups
  • Introduced 'law of octaves' when he noticed that the properties of every eighth element seemed similar
  • Ordered elements by atomic number and their properties, but crucially left gaps for unknown elements, which when discovered matched his predictions
• Metals are found on the left and bottom of the Periodic Table, while non-metals are found on the right and top
• Metals


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


  Tend to gain electrons, forming negative ions
• Noble gases


  Have unreactive because of their very stable electron arrangements (i.e. they have a full outer shell of electrons)
• Group 1 metals (alkali metals)


  • Melting point / boiling point decrease down the group
  • All react with water to produce a metal hydroxide solution (an alkali) and hydrogen gas
  • The reaction gets more violent down the group
• Group 7 elements


  • Melting points / boiling points increase down the group
  • Are poor conductors of heat and electricity
  • Are all toxic and have coloured vapours
  • Exist as diatomic (ie. 2-atom) molecules, e.g. F2, Cl2, etc.
  • A more reactive halogen can displace a less reactive halogen from a solution of one of its salts
• Group 0 (noble gases)


  • Unreactive (inert) as they have a full outer shell - stable
  • Boiling point increases down the group
• Transition metals


  • Good conductors of electricity and heat
  • Hard and strong
  • Have high densities
  • High melting point (except mercury, Hg, which exists as a liquid at room temperature)
  • Stronger, harder, have higher melting points and densities, and are less reactive than Group 1 metals
  • Do not react vigorously with oxygen or water
  • Form coloured compounds
  • Can form more than one ion
• Transition metals and their compounds are important industrial catalysts
• States symbols


  • (s) = solid
  • (l) liquid
  • (g) = gas
  • (aq) = aqueous (dissolve in water)
• Ionic bonding


  • Occurs when metals are combined with non-metals
  • Electrons in the outer shell of the metal atom are transferred to the non-metal
  • The charge on an ion relates to where the element is on the periodic table
• Ionic structure


  • Regular giant structure of ions often referred to as a giant ionic lattice
  • Ions are held together by strong electrostatic forces of attraction between oppositely charged ions
  • Ionic compounds have a high melting and boiling point due to the strong electrostatic forces which require a lot of energy to break
  • Can not conduct electricity when solid, but can conduct when molten or dissolved in water because then ions are free to move so charge can flow
• Metallic bonding


  • The electrons in the outer shell of metal atoms are delocalised (i.e. are free to move throughout the whole structure)
  • The attraction between negative delocalised electrons and the positive metal ions creates a strong electrostatic force of attraction
  • Metals have strong electrostatic forces and tend to have high melting points
  • Metals can conduct electricity and thermal energy because the delocalised electrons can move freely
• Alloys


  • Metals that are mixed with other elements
  • The atoms are all different sizes, which means the layers can no longer slide over one another, making alloys harder
• Covalent bonding


  • Occurs between two non-metal elements
  • Each pair of shared electrons is a covalent bond
• Simple covalent molecules


  • Small molecules made up of two or more non-metals
  • Usually exist as gases or liquids which have relatively low melting and boiling points
  • This is due to the molecules having weak (intermolecular) forces between the molecules, not the strong covalent bonds
  • Intermolecular forces increase with the size of the molecules, so the larger the molecule, the higher the melting and boiling point
  • Do not conduct electricity as the molecules have no charged particles (i.e. no free electrons or free ions!)
• Bonding models


  • Displayed formula
  • Dot-cross diagram
  • 2D ball & stick model
  • 3D ball & stick model
• Nanoscience


  • Refers to structures which are 1-100nm in size
  • Nanoparticles are smaller than fine particles and coarse particles
  • Fine particles have a diameter = 100 – 2500nm
  • Coarse particles have a diameter = 2500 – 50000nm
  • Coarse particles are often referred to as dust