(BONDING AND CALCULATIONS, 2a) 1

Atoms, compounds and isotopes
1. mass number: total number of protons and neutrons
  1. number of neutrons; mass number minus atomic number
    1. atomic number: number of protons
2. proton: mass 1, charge +1
  1. neutron: mass 1, charge 0
    1. electron: mass 1/2000, charge -1
3. compounds are chemically bonded
  1. compounds are formed when atoms of 2 or more elements are chemically combined together
4. isotopes are the same except for an extra electron
  1. isotopes are different atomic forms of the same element, which have the SAME no. of PROTONS but DIFFERENT no. of NEUTRONS
5. isotopes e.g. C12 = 6 neutrons and C14 = 8 neutrons but both have 6 protons & 6 electrons
Ionic bonding
1. ionic bonding = transferring electrons
  1. a shell with one electron wants to get rid of it
    1. a shell with 7 electrons wants to get one extra electron
2. very strong electrostatic forces of attraction between oppositely charged ions, in all directions
  1. atoms lose or gain electrons to form charged particles (called ions)
3. ionic compounds all have similar properties
  1. high melting points and high boiling points - due to strong attraction between ions
  2. dissolves easily
4. ionic compounds have a regular lattice stucture
  1. they always have giant ionic lattices
    1. the ions form a closely packed regular lattice arrangement
5. ions have the electronic structure of a noble gas
6. charge on the positive ions is the same as the group number of the element
7. overall charge of any compound is zero
8. sodium chloride = NaCl
  1. magnesium chloride = NgCl 2
covalent bonding
1. = sharing electrons
2. only share electrons in their outer shells (highest energy levels)
3. both atoms want a full outer shell
  1. having a full outer shell gives them the electronic structure of a noble gas
4. simple molecular substances
  1. forces of attraction between these molecules are very weak
  2. melting/boiling points = very low
  3. molecules are easily parted from each other
  4. don't conduct electricity
5. giant covalent structures are macromolecules
  1. no charged ions
  2. all the atoms are bonded to each other by strong covalent bonds
  3. very high melting/boiling points
  4. don't conduct electricity
  5. main examples are diamond and graphite
metallic structures
1. metal properties are all due to the sea of free electrons
  1. good conductors of heat/electricity
2. electrons are free to move
3. regular structure, strong forces of electrostatic attraction between the +ve metal ions and the -ve electrons
4. allow layers of atoms to slide over each other - metals can be bent/shaped
new materials
1. smart materials - e.g. shape memory alloy
2. when it's cool, you can bend it
  1. if heated above certain temp. it goes back to 'remembered shape'
3. Nitinol is also used for dental braces - warms in mouth and tries to return to a 'remembered shaoe', gently pulling teeth with
nanoparticles (nanoscience)
1. high surface area to volume ratio
2. new cosmetics e.g. sun tan cream/deodorant made using nanoparticles
3. polymers
  1. nanotubes conduct electricity
  2. forces between molecules determine properties of plastics
    1. weak; held together by weak intermolecular forces/free to slide over each other
      1. strong; stronger intermolecular forces between polymer chains (crosslinks) that hold the chains firmly together
  3. thermosoftening; forces between chains = easy to overcome...easy to melt plastic. When cooled, hardens into new shape
  4. thermosetting; have crosslinks...solid structure, doesn't soften when it's heated, stong, hard, rigid

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(BONDING AND CALCULATIONS, 2a) 1

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	Created by Eleanor Rose over 9 years ago