1. Atomic Structure, Period Table, Ionic Bonding

• atom: the smallest particle of an element
• molecule: made of a fixed number of atoms covalently bonded together
• an atom consists of a nucleus composed of protons and neutrons

  they are surrounded by electrons, orbiting in shells (energy levels)
• proton mass and charge: 1, +1

  neutron mass and charge: 1, 0

  electron mass and charge: undefined, -1

  
  

  the nucleus is positively charged

  electrons are negatively charged

  atoms are neutral
• atomic number: number of protons in an atom

  
  

  number at the bottom of the element
• mass number: number of protons and neutrons in an atom

  
  

  number at the top of the element
• isotopes: atoms with the same number of protons but different numbers of neutrons
• relative atomic mass (Ar): average mass of an atom compared to the 1/12th mass of carbon-12
• isotopic abundances:

  1. multiply mass of each isotope by relative abundance (%)
  2. add them together
  3. divide the sum by 100

  
• periodic table:

  • columns are called groups, indicates the number of electrons on the outer shell
  • rows are called periods, indicates the number of shells in an atom
• metals

  • conduct electricity
  • have oxides which are basic, reacting with acids to give a salt and water
• non-metals

  • do not conduct electricity (except for graphite)
  • have oxides which are acidic or neutral
• metals are on the left

  non-metals are on the right

  semimetals are in a staircase structure near the right

  
• noble gases have a full outer shell of electrons so they are unreactive as they do not need to gain or lose electrons
• relative formula mass (Mr): sum of relative atomic masses (Ar)
• mole: the amount of a substance that contains the same number of particles as there are atoms in 12 grams of carbon-12
• mole = mass/Mr