3 Atomic Structure

• Everything around us is made up of atoms, including ourselves
• The atom is the simplest, smallest unit of an element that contains its properties
• There are 118 different kinds of atoms as there are 118 different elements found on earth
• Atoms are too small to be seen even with a microscope
• Atom

  The smallest particle that can still have the chemical characteristics of an element
• Atoms


  • They have sub-atomic particles within them
  • Each element is made up of its own type of atoms
• Gold and silver are different elements that behave differently because they have different numbers of sub-atomic particles
• The three main sub-atomic particles

  • Protons
  • Neutrons
  • Electrons
• Proton (atomic) number (Z)


  Number of protons in the nucleus

  
• Nucleon (mass) number (A)


  Total number of protons and neutrons in the nucleus
• Number of neutrons


  Nucleon number (A) - Proton number (Z)
• Nuclide notation


  Shows the proton (atomic) number (Z) and nucleon (mass) number (A)

  
• The atomic symbol and proton number both indicate the type of element the atom belongs to
• Ion


  The particle formed when an atom or group of atoms gains or loses electron(s), but the number of protons and neutrons remains the same
• Ions


  • Ca2+
  • O2-
• Isotopes


  Atoms of the same element that have the same proton (atomic) number but different nucleon (mass) numbers
• The presence of isotopes in different percentage abundance explains why the mass number of some elements in the Periodic Table are not whole numbers
• The mass of an atom of an element is an average mass of the isotopes that make up that element
• Most elements occur naturally as isotopes
• Hydrogen isotopes


  • Hydrogen-1
  • Hydrogen-2
  • Hydrogen-3
• Isotopes


  • They have similar chemical properties but may have different physical properties
• This means they have different numbers of neutrons.
• Since the proton number remains unchanged, the isotopes belong to the same element