4 Chemical Bonding

• Noble gases


  Atoms with fully filled valence shells of electrons

  
• Noble gases are inert and exist as monoatomic gases

  
• Noble gases and their electronic configurations

  • Helium (2)
  • Neon (2, 8)
  • Argon (2, 8, 8)

  
• Atoms that are not noble gases lose, gain or share electrons to fill up their outermost electron shells

  
• Noble gases


  • They have stable duplet or octet electronic configurations

  
• Noble gases are monoatomic
• Other atoms tend to lose, gain or share electrons to attain a noble gas electronic configuration
• Positive ion (cation)


  Formed when an atom (usually a metal) loses electron(s)

  
• Negative ion (anion)


  Formed when an atom (usually a non-metal) gains electron(s)

  
• Common cations


  • Hydrogen (H+)
  • Sodium (Na+)
  • Potassium (K+)
  • Silver (Ag+)
  • Ammonium (NH4+)
  • Magnesium (Mg2+)
  • Calcium (Ca2+)
  • Barium (Ba2+)
  • Iron(II) (Fe2+)
  • Copper(II) (Cu2+)
  • Zinc (Zn2+)
  • Lead(II) (Pb2+)
  • Iron(III) (Fe3+)
  • Lead(III) (Pb3+)

  
• Common anions


  • Fluoride (F-)
  • Chloride (Cl-)
  • Bromide (Br-)
  • Iodide (I-)
  • Hydroxide (OH-)
  • Nitrate (NO3-)
  • Manganate(VII) (MnO4-)
  • Oxide (O2-)
  • Carbonate (CO32-)
  • Sulfate (SO42-)
  • Phosphate (PO43-)
• Ionic bond


  The mutual electrostatic attraction between ions of opposite charges
• Ionic compounds are electrically neutral
• Ionic compound formula


  Determined by the ratio of the ions in the compound
• Ionic solids

  • Exist as giant ionic crystal lattices, a 3D structure of alternating positive and negative ions
• Covalent bond


  Formed when atoms share electrons to attain noble gas electronic configurations
• Sand and water are examples of covalent compounds
• Atoms in covalent compounds share their valence electrons during bonding
• Covalent bond (chlorine)

  Chlorine atom shares an electron to attain a noble gas electronic configuration

  
• Covalent bonds


  Bonds formed when atoms share electrons to attain noble gas electronic configurations
• Sand is made up of silicon and oxygen
• Water is made up of hydrogen and oxygen
• Silicon, oxygen and hydrogen are non-metals
• Covalent compounds


  Compounds where atoms share electrons
• Covalent bond


  Bond formed when atoms share electrons to attain noble gas electronic configurations
• Chlorine atom


  • Electronic configuration of 2, 8, 7
  • Needs 1 electron to complete outermost shell
  • Valency of 1

  
• Formation of covalent bond between chlorine atoms

  1. Two chlorine atoms share 1 electron each

  2. Resulting in electronic configuration of 2, 8, 8

  
• Valency


  Number of electron(s) that must be lost, gained or shared for an atom to attain a noble gas electronic configuration

  
• Oxygen atom


  • Electronic configuration of 2, 6
  • Valency of 2

  
• Formation of double covalent bond between oxygen atoms

  1. Two oxygen atoms share 2 electrons each

  2. Resulting in electronic configuration of 2, 8
• Nitrogen atom


  • Electronic configuration of 2, 5
  • Valency of 3
• Formation of triple covalent bond between nitrogen atoms

  1. Two nitrogen atoms share 3 electrons each

  2. Resulting in electronic configuration of 2, 8
• Covalent bonding


  • Can occur between multiple atoms
  • An atom can share its electrons with more than one other atom
• Formation of covalent bond in water molecule

  1. Two hydrogen atoms and 1 oxygen atom

  2. Hydrogen has valency of 1, oxygen has valency of 2

  
• Covalent molecule


  Can be made from atoms of the same or different elements
• Simple molecules


  • Have a countable number of atoms in a fixed ratio
  • Examples: water, wax
• Giant molecules


  • Have a practically uncountable number of atoms
  • Examples: diamond, sand (silicon dioxide)
• Determining number of covalent bonds formed

  1. By comparing the valences of the atoms

  2. Example: ammonia has 3 hydrogen atoms sharing electrons with 1 nitrogen atom

  
• Sharing capacity of common elements

  • Name of element
  • Number of electrons in outermost shell
  • Number of electrons it normally shares
  • Most common number of covalent bonds it can form
  • Group number in periodic table
• A covalent bond is formed when atoms share electrons to attain noble gas electronic configurations