Bonding

• Chemical Bonding

  Attractive forces that hold atoms together in a new substance
• Chemical Formula

  A way of representing a compound using symbols for the atoms present and numbers to show how many atoms of each element are present
• Most of the materials around us are made from combinations of elements
• Compound

  A substance that is made up of two or more different elements combined together chemically
• When elements combine to form compounds, there are attractive forces that hold the atoms together in this new substance
• Chemical Bonds

  The attractive forces that hold atoms together in a compound
• Octet Rule


  • When bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost energy level
  • There are exceptions to the octet rule, such as transition metals and elements near helium
• Ionic Bonding - Transfer of Electrons

  1. Atoms gain or lose electrons to obtain the electron configuration of a noble gas

  2. Positively charged ions (cations) are formed when atoms lose electrons

  3. Negatively charged ions (anions) are formed when atoms gain electrons

  4. Ionic bonds are formed by the force of attraction between oppositely charged ions
• Ionic Bond


  The force of attraction between oppositely charged ions in a compound
• Ionic bonds are always formed by the complete transfer of electrons from one atom to another
• Sodium chloride has a cubic crystal structure with a regular three-dimensional arrangement of sodium and chloride ions
• Salt is an essential part of our diet, but too much can cause high blood pressure
• Writing Formulas of Ionic Compounds

  1. Ionic compounds are usually formed between metals and non-metals

  2. The formula must have the same number of positive and negative charges

  3. Formulas can be written using dot-and-cross diagrams or Bohr-type circle diagrams
• Common Group Ions

  • Hydroxide ion (OH-)
  • Nitrate ion (NO3-)
  • Hydrogencarbonate ion (HCO3-)
  • Permanganate ion (MnO4-)
  • Carbonate ion (CO3(2-))
  • Chromate ion (CrO4(2-))
  • Dichromate ion (Cr2O7(2-))
  • Sulfate ion (SO4(2-))
  • Sulfite ion (SO3(2-))
  • Thiosulfate ion (S2O3(2-))
  • Phosphate ion (PO4(3-))
  • Ammonium ion (NH4+)
• Writing Formulas of Compounds Containing Transition Metals

  1. Transition metals often have variable valency

  2. Formulas must indicate the charge on the transition metal ion using Roman numerals in brackets
• The d-block elements, some of which are transition metals, often have variable valency
• FeCl2


  Iron(II) chloride
• FeCl3

  Iron(III) chloride
• Cu2O

  Copper(I) oxide
• CuO

  Copper(II) oxide
• Cr3+

  Chromium(III) ions
• Na2Cr2O7

  Sodium dichromate(VI)
• MnO2

  Manganese(IV) oxide
• MnSO4

  Manganese(II) sulfate
• 1. block elements

  • Solutions containing ions of d-block elements
• Transition metals

  • Exhibit variable valency
  • Form coloured compounds
  • Widely used as catalysts
• Transition metal


  One that forms at least one ion with a partially filled d sublevel
• Scandium and zinc are not considered transition metals
• • Compounds whose names end in -ide contain just two elements
  • Compounds whose names end in -ate contain oxygen as well as the other two elements
• Covalent bond

  Formed by the sharing of a pair of electrons between atoms
• Single bond

  Formed by the sharing of one pair of electrons
• Double bond

  Formed by the sharing of two pairs of electrons
• Triple bond

  Formed by the sharing of three pairs of electrons
• Sigma bond

  Formed by the head-on overlap of atomic orbitals
• Pi bond

  Formed by the sideways overlap of atomic orbitals
• Sigma bonds are stronger than pi bonds
• Ionic compounds

  • Usually consist of a network of ions
  • Are usually difficult to cut
  • Have high melting and boiling points
  • Do not conduct electricity in the solid state
• Covalent compounds

  • Generally consist of individual molecules
  • Are usually quite soft
  • Have low melting and boiling points
  • Do not conduct electricity in the solid state
• Covalent compounds

  • Consist of separate molecules
  • Molecules have particular shapes
• VSEPR Theory

  • Proposed by Sidgwick and Powell in 1940
  • Explains the shapes of molecules
  • Depends on the number of pairs of electrons around the central atom
  • Electrons repel each other and arrange themselves to be as far apart as possible