Bonding Lectures PPT

• Metals and non-metals

  Separated by a 'staircase' on the periodic table
• Types of bonding between elements

  1. Ionic Bonding

  3. Covalent Bonding

  4. Metallic Bonding
• Electron configurations

  • Electrons fill the shells from the innermost shell first
  • Electrons can be shown as dots or crosses on the diagram
  • An atom has the same number of electrons in its outer shell as its group in the periodic table
• Metal ion configurations

  • Metals lose their outer shell electrons to gain a full outer shell or noble gas configuration
  • Metals form positively charged ions
  • The charge on a metal ion is the same as its group in the periodic table
  • Ions are shown in square brackets
  • It is usually acceptable just to show the outer shell of an ion
  • A metal ion may be shown full or empty
  • Mg 2+ can also be written 2.8
• Non-metal ion configurations

  • Non-metals gain electrons to achieve a full outer shell or noble gas configuration
  • Non-metals form negatively charged ions
  • Ions are shown in square brackets
  • It is usually acceptable just to show the outer shell of an ion
  • In this diagram the electrons from the oxygen atom have been shown as crosses and the electrons gained shown as dots
  • O 2- can also be written 2.8
• When metals and non-metals react

  1. Electrons are transferred from the metal to the non metal

  2. Both the metal and the non-metal gain a full outer shell or noble gas configuration
• Ionic bonding

  The electrostatic attraction between oppositely charged ions
• Number of ions in an ionic compound

  • Depends on their charges
  • The overall number of positive and negative charges must be the same for a neutral ionic compound to be formed
• Common polyatomic ions

  • Ammonium NH4+
  • Nitrate NO3-
  • Hydroxide OH-
  • Sulfate SO4 2-
  • Phosphate PO4 3-
  • Carbonate CO3 2-
• Determining the formula of an ionic compound

  The formula comes from the number of positive and negative ions it needs to balance the charge overall
• Ionic lattice

  • An ionic compound forms a lattice/giant ionic lattice structure
  • It consists of a regular arrangement of ions held together by strong electrostatic forces between oppositely charged ions
  • These electrostatic forces are called ionic bonds
• Properties of Ionic Compounds

  • High melting points and boiling points because a large amount of energy is required to break the strong electrostatic forces of attraction in all directions between the ions the lattice
  • Conduct electricity when molten (liquid) or dissolved in water because the charged ions are free to move around
  • Do not conduct electricity when solid as the charged particles are not free to move around
• Representing ionic compounds in 2D: Balls Model

  • Advantages: It shows how each ion is surrounded by oppositely charged ions, It shows the ions closer together and without using sticks to connect them
  • Disadvantages: It only shows the ions in two dimensions, It doesn't show the difference in ionic size
• Representing ionic compounds in 2D: Charged Particles Model

  • Advantages: Shows the electronic structure of ions, Shows the charges on the ions, Shows the ratio of ions in the formula
  • Disadvantages: Doesn't show how the ions are arranged in the lattice
• Representing ionic compounds in 3D: Ball and Stick Model

  • Advantages: Shows how the ions are organised in the lattice, Arrangement of ions can be seen, and the empirical formula determined, Represents the structure in 3D
  • Disadvantages: The ions are not so widely spaced, and the sticks do not really exist, It doesn't show the difference in ionic size
• Representing ionic compounds in 3D: Balls Model

  • Advantages: It shows the structure in 3D, The ions are close together, No sticks
  • Disadvantages: Difficult to determine the arrangement of ions, Doesn't show the difference in ionic size
• Unit cells

  • A unit cell shows the number and arrangement of ions in an ionic compound
  • The empirical formula of an ionic compound can be determined from its unit cell by counting the number of ions in each position
  • Ions in the corners (at a vertex) each one in the unit cell counts 1
  • Ions on an edge each one in the unit cell counts 1/4
  • Ions on a face each one in the unit cell counts 1/2
  • Ions completely within the unit cell (in the middle) each one in the unit cell counts 1
• Typical unit cells

  • 4 of each type of atom on the corners 1:1
  • 8 atoms on the corners (1), 1 in the middle (1) 1:1
  • 12 atoms on the edges (3), 1 in the middle (1) 3:1
  • 6 atoms on the faces (3), 8 atoms on the corners (1) 3:1
• Covalent bonding

  • A single covalent bond is formed when a pair of electrons is shared between two atoms
  • The atoms sharing electrons usually achieve a full outer shell, or noble gas configuration, of electrons
• Types of covalent substances

  Covalently bonded substances may consist of small molecules, large molecules (macromolecules) and giant covalent structures
• Sizes of atoms, bonds and molecules

  • 1 Å = 1 x 10-10 m
  • The atomic radii of neutral atoms range between 0.3 and 2Å. A carbon atom is 0.7Å.
  • As a rule of thumb the length of a single bond between two atoms is approximately the sum of the radii of the two atoms
  • Double and triple bonds get progressively shorter as there is greater overlap
  • Carbon dioxide's molecular diameter can be estimated using the atomic radius of carbon (0.7Å) and oxygen (0.6Å), giving (0.7 x 2) + (0.6 x 4) = 3.8Å. The true value is lower at 3.2Å because the molecule contains two double bonds which reduce the distance by 2Å each
• Coordinate bonding (sometimes called dative covalent)


  When both of the electrons in a coordinate bond have been supplied by one of the atoms
• Coordinate bonding examples

  • NH4+ the ammonium ion
  • Water can also gain a proton to form the hydronium or H3O+ ion
  • AlCl3 two molecules of AlCl3 coordinate bond to each other to form Al2Cl6 which is called a DIMER
• Forces between molecules

  • Substances consisting of small molecules have weak intermolecular forces between their molecules
  • This means that at room temperature most molecular substances are gases, liquids or low melting point solids
  • Melting point increases with molecular mass
• Melting and boiling molecular substances

  It is relatively easy to overcome the weak intermolecular forces when a substance made of molecules such as water or iodine is heated. It is these forces that are broken when melting and boiling, not the very strong covalent bonds between the atoms.
• Other properties of molecular substances

  • Simple molecular substances do not generally contain charged particles, so they have poor conduction of electricity
  • They do not readily dissolve in water
• Giant covalent structures / macromolecular

  • It is very difficult to break the many covalent bonds between the atoms
  • Giant covalent structures have very high melting points
  • This means they are solid at room temperature
  • All the atoms within a giant covalent structure are connected to other atoms by strong covalent bonds in a giant lattice
• Diamond

  • Diamond is carbon in the form of a giant covalent structure where each atom makes four strong covalent bonds to other carbon atoms
  • Diamond is very hard, insoluble, does not conduct and has a very high melting point
  • Diamond is used in jewellery and in cutting tools
• Graphite

  • Graphite is carbon in the form of a layered giant covalent structure where each atom makes three bonds to other carbon atoms and carbon's fourth outer electron is delocalised between the hexagonal sheets of carbon atoms
  • Graphite is much softer than diamond because its layers can rub away due to the weak intermolecular forces between them. It can therefore be used as a lubricant
  • Graphite has a high melting point because the three covalent bonds between carbon atoms are difficult to break
  • The delocalised electron means that graphite can conduct electricity so it can be used to make electrodes
• Silicon dioxide

  • Silicon dioxide SiO2 is found as the crystal quartz
  • It is the main constituent in most sand
  • Is is used in making glass
  • Silica is used as an electrical insulator in thin layers on microchips
  • Silicon dioxide (silica) has a giant covalent structure similar to diamond
  • Each silicon atom makes four covalent bonds and each oxygen atom makes two covalent bonds
  • Silicon has a high melting point and is very hard
• Graphene

  Graphene is a single layer of graphite and due to its delocalised electrons it is a semiconductor useful in computing
• Fullerenes

  Fullerenes are molecules of carbon atoms that are spherical, tubular or other hollow shapes. For example, the football shaped Buckminsterfullerene with the formula C60.
• Metallic Bonding

  • Metallic bonding is the electrostatic attraction between positively charged metal ions and delocalised electrons
  • The electrons in the outer shell of metal atoms are delocalised and free to move within the structure. They are sometimes described as a "sea of delocalised electrons"
• Metal Ions

  • Loss of the outer shell electrons leaves more stable metal ions
  • The metals ions in group 1, 2 and 3 have noble gas configurations
  • The electrostatic attraction in metals is strong so metallic bonding is strong
• Metallic Bonding(Definition)

  The electrostatic attraction between positively charged metal ions and delocalised electrons
• Metal Ions


  • Loss of the outer shell electrons leaves more stable metal ions
  • The metals ions in group 1, 2 and 3 have noble gas configurations
• Metallic Bonding


  • The electrostatic attraction in metals is strong so metallic bonding is strong
  • Delocalised electrons are free to move through the structure which means metals conduct electricity and heat (thermal energy)
  • The higher the charge on the metal ion the stronger the bonding, so group 3 aluminium has higher melting point than group 2 magnesium or group 1 sodium
• Pure Metals

  Can be too soft because the layers slide easily
• Pure Metals

  • Malleable and ductile because the layers of ions can slide over one another and the electrons can move and reposition themselves
• Alloys

  • Mixtures of metals and sometimes other elements such as carbon which affect the properties of the metal by disturbing the lattice
  • This generally reduces malleability by preventing the layers from sliding over one another hardening the material