Atomic Structure

• Atom


  The basic unit of chemical elements
• Atoms


  • Contain subatomic particles in their nucleus and in the electron cloud that surrounds the nucleus
  • Subatomic particles include protons, neutrons, and electrons
• Protons


  Have a positive electrical charge
• Neutrons


  Are uncharged
• Electrons


  Have a negative charge
• The number of protons and electrons are equal, so atoms are electrically neutral particles
• Electrons in atoms


  • Arranged in simple rings or shells surrounding the nucleus
  • Each shell represents a different energy level
  • Each shell can only hold a certain maximum number of electrons
• In chemical reactions between atoms, only the electrons in the outermost shell participate in the resulting chemical bond
• Stability of atoms


  • Atoms with only one energy level or shell require 2 electrons for stability
  • Atoms with more than one energy level or shell require 8 electrons in the outermost shell for stability
• Helium


  • Has 1 shell or energy level and contains 2 electrons, so it is stable
• Hydrogen


  • Has 1 ring or shell and possesses only one electron, so it is chemically reactive
• Neon


  • Has 8 electrons in its outermost shell, so it is stable
• Oxygen


  • Has only 6 electrons in its outmost shell, so it is chemically reactive
• Octet rule


  Atoms that have fewer than 8 electrons in their outermost shells will try to share, gain, or lose electrons in order to become stable
• There are some exceptions to the octet rule, such as hydrogen and helium which only have one energy level or shell