Unit 5 - Chemical Formulas and Chemical Compounds

• chemical formula: a type of notation made with symbols for the elements and numbers
• molecule - a single atom or a group of atoms covalently bonded together.
• diatomic - molecule that consists of two atoms of the same element bonded together.

  
  

  (diatomic - aluminum, bromine, calcium, chlorine, oxygen, fluorine, hydrogen)
• C8

  8 is the subscript
• molecular - number of atoms of each element in one molecule of the substance. the true formula for the molecule.
• empirical - simplest whole-number ratio in which the atoms of the elements are present in the compound.
• structural - shows which atoms are joined together in a molecule.
• electrostatic interactions - any type of attractive forces between opposite charges. all bonds form from electrostatic forces.
• ionic substances - the individuals atoms have charges because electrons are transferred. the compound doesn't have a charge.
• properties of ionic compounds:

  • high melting and boiling points
  • conduct electricity in liquid or aqueous state (electrolytes)
  • dissolve in water
  • solids at room temp
• covalent substances - the individuals atoms have an oxidation number which indicating the number of electrons they are sharing from their original valence electrons.
• properties of covalent molecules:

  • low melting and boiling points
  • do not conduct electricity in any state (non-electrolytes)
  • may dissolve in water (will dissolve if polar covalent, won't dissolve if non-polar covalent)
  • can be liquid, solid, or gas
• oxidation number and charges - describe the number of electrons that a molecule is sharing in covalent bonds or transferring (losing/gaining) to another atom in ionic bonds.
• univalent - one charge

  alkali metals, alkaline earth metals, hydrogen (1), beryllium (2), silver (1), aluminum (3), zinc (2)
• polyatomic ions are covalently bonded molecules that have an overall charge and will combine with other atoms to from ionic compounds.

  
  

  oxyanion is a polyatomic ion that has oxygen.
• nomenclature - dictates how compounds are name to ensure that everyone does it the same way.
• oxidation # for a covalent compound indicates the number of shared elections.
• Binary - special types of ionic compounds and will always start with a hydrogen (hydro). Ends in ic and add acid at the end.

  *ones that don't have oxygen (hydrofluoric)
• Oxyacids

  starts with h but not hydro and name of polyatomic ion. ate -> ic and ite -> ous.
• hydrates are ionic compounds that have water attached to the ionic compound. many ionic compounds absorb water from air and they use greek prefixes.
• organics are covalently bonded compound.

  hydrocarbons are composed of carbons and hydrogen and are the simplest organic compounds
• prefixes:

  mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca

  meth, eth, prop, but, pent, hex, hept, oct, non, deca
• alkanes - single bonds Cn H2n+2
• alkenes - double covalent bonds Cn H2n
• alkynes - triple bonds Cn H2n-2
• hydrocarbon rings - most important class of these compounds are aromatic hydrocarbons (simplest form of benzene)