Periodic table

• The nucleus contains the genetic material (DNA) that controls all cell activities.
• Periodic table


  Diagram that shows the elements arranged by their properties
• Main groups in the periodic table

  • Alkali metals
  • Halogens
  • Noble gases
  • Transition metals
• Element


  Substance made up of one type of atom
• Compound


  Substance made of two or more types of atoms that are chemically bonded together
• Mixture


  Consists of two or more substances that are not chemically bonded together
• Mass number


  Number at the top of an element symbol, equal to the number of protons plus neutrons
• Atomic number


  Number at the bottom of an element symbol, equal to the number of protons
• Protons


  Positively charged particles in the nucleus of an atom
• Electrons


  Negatively charged particles that orbit the nucleus of an atom
• Neutrons


  Neutral particles in the nucleus of an atom
• Electron shells


  Regions around the nucleus where electrons are found, with a maximum number of electrons in each shell
• Electron shell capacities


  • First shell: 2 electrons
  • Second shell: 8 electrons
  • Third shell: 8 or 18 electrons
• Metals


  • Form positive ions
  • Good conductors of heat and electricity
  • Have high melting and boiling points
  • Ductile and malleable
• Non-metals


  • Form negative ions
  • Insulators
  • Have low melting and boiling points
• Group 1 metals (alkali metals)


  Reactivity increases down the group
• Reasons for increasing reactivity of alkali metals down the group

  • Easier to lose outer electron
  • Larger atom size
  • More shielding
  • Less attraction between nucleus and outer electron
• Alkali metals


  • Highly reactive with oxygen, water, and chlorine
  • Reactivity increases down the group
• Reactions of alkali metals

  1. Reaction with oxygen: form metal oxide

  2. Reaction with water: form metal hydroxide and hydrogen gas

  3. Reaction with chlorine: form metal chloride
• Group 7 elements (halogens)

  Reactivity decreases down the group
• Reasons for decreasing reactivity of halogens down the group

  • Harder to gain outer electron
  • Larger atom size
  • More shielding
  • Less attraction between nucleus and outer electron
• Halogens


  • Exist as diatomic molecules
  • Melting and boiling points increase down the group
  • Reactivity decreases down the group
• Group 0 elements (noble gases)


  Not reactive at all, have full outer electron shells