Ch2 - Atomic Structure

• Element


  A substance that cannot be further divided into simpler substances by chemical means 
• Compound


  A substance formed by two or more elements chemically combined
• Mixture


  Two or more substances mixed together but not chemically combined 
• Atom


  The smallest particle of an element
• An atom is made of a central nucleus containing protons and neutrons surrounded by electrons in shells
• Relative mass of electron

  1/1840
• Relative charge of electron

  -1
• Relative mass of proton

  1
• Relative charge of proton

  +1
• Relative mass of neutron

  1
• Relative charge of neutron

  0
• Proton/Atomic number


  Number of protons in the nucleus
• Mass/Nucleon number


  Total number of protons and neutrons in the nucleus
• Proton/Atomic number is denoted by Z
• Mass/Nucleon number is denoted by A
• Isotopes


  Atoms of the same element that have the same number of protons but different numbers of neutrons
• Isotopes of the same element have the same chemical properties because they have the same electronic configuration
• Relative atomic mass 


  The average mass of an atom when compared to 1/2 of the mass of a carbon-12 atom
• Relative atomic mass is denotaed by Ar
• Hydrogen isotopes


  Hydrogen, Deuterium, Tritium
• Carbon isotopes

  Carbon-12, Carbon-13, Carbon-14
• Neon isotopes

  Neon-20, Neon-21, Neon-22
• Chlorine isotopes

  Chlorine-35, Chlorine-37
• Tritium and carbon-14 are radioisotopes isotopes because their nuclei are unstable
• Hydrogen and deuterium are naturally occuring isotopes
• Isotopes of the same element differ in physical properties such as density and rate of diffusion
• The number of occupied energy levels/shells in an atom tells you the period number of the element
• Group VIII elements are called noble gases, they have a full outer shell which makes them unreactive