Y9 Periodic Table & Reactivity

• Periodic table

  Arranges all of the known elements in order of increasing atomic number
• Atomic mass

  Sum of the protons and neutrons
• Atom

  The basic unit of a chemical element
• Electron

  Negatively charged subatomic particle located outside the nucleus
• Atomic structure

  • Protons
  • Neutrons
  • Electrons
• Valence electron

  An electron in one of the outer shells of an atom that can participate in forming chemical bonds with other atoms
• Electron arrangement

  1st shell can hold up to 2 electrons, 2nd shell can hold up to 8 electrons, 3rd shell can hold up to 18 electrons
• Number of valence electrons

  • Determines the element’s reactivity
• Number of valence electrons

  The outermost electrons in an atom involved in chemical bonding
• 4 or 8 valence electrons


  Stable and less reactive state
• Fewer than 4 valence electrons


  Unstable and highly reactive, tends to gain electrons
• More than 4 valence electrons


  Unstable and highly reactive, tends to lose electrons