chap2. atomic structure

• Atom


  A particle which contains the same number of protons and electrons
• Protons


  Positively charged particles found in the nucleus of an atom
• Electrons


  Negatively charged particles found in the outer part of an atom
• Neutrons


  Neutral particles found in the nucleus of an atom
• Relative charges and approximate relative masses

  Protons have a positive charge, electrons have a negative charge, and neutrons have no charge. Protons and neutrons have approximately the same mass, which is much greater than the mass of an electron
• Atoms are electrically neutral because they have no overall charge
• Equal numbers of protons and electrons

  The charges cancel (net charge = 0)
• Structure of an atom

  An atom has a nucleus containing protons and neutrons, and outer parts containing electrons
• Isotopes


  Atoms of the same element which have the same proton/atomic number but different mass numbers
• Valence electrons


  • Tell us the Group number of the element
  • Are the electrons in the outer/outermost/valence shell
• Electron distribution/configuration/structure


  Shows how electrons are arranged in the shells of an atom
• Elements of the Periodic Table

  Arranged according to their proton/atomic number
• Nucleon number (mass number)

  Total number of protons and neutrons in the nucleus of an atom
• Atoms contain charged particles but they are electrically neutral because they have no overall charge - This is because there are equal numbers of protons and electrons and the charges cancel out each other
• 8 Isotopes

  (a) Isotopes are atoms of the same element which have the same proton number but

  different mass (nucleon) numbers.

  (b) *The mass number of chlorine in the Periodic Table is given as 35.5 because it is

  the weighted average of the chlorine isotopes, Cl-35 and Cl-37.