Atomic Structure

Atomic Structure

1. The nucleus

   • Protons
     • Charge +1, mass 1
     • Number of protons determines what element an atom is
   • Neutrons
     • Charge 0, mass 1
     • Isotopes of an element have the SAME NUMBER OF PROTONS BUT DIFFERENT NUMBER OF NEUTRONS
       • Have the SAME chemical properties as they have the same number of electrons

2. Electrons

   • Charge -1, mass v. small (1/1836 - approx. 0)
     • ATOMS of an element have equal numbers of protons and electrons
       • Atoms can gain or lose electrons to become IONS
         • Metal atoms lose electrons to become positive ions - CATIONS
         • Non-metal atoms gain electrons to become negative ions - ANIONS
   • Orbit the nucleus in energy "levels" or "shells"
     • A full outer energy shell is stable
       • Noble gases have full outer shells and are unreactive or INERT
     • Electrons fill the inner energy levels before filling the outer energy levels
       • Maximum number of electrons in each energy level = 2,8,8
     • Row on periodic table (period) = no of electron shells
       • Group number on periodic table = number of electrons IN OUTER SHELL

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