covalent bonding

• Covalent bonds are formed by the sharing of electrons between atoms.
• The number of shared pairs of electrons determines the type of covalent bond (single, double or triple).
• A single covalent bond is formed when two atoms share one pair of electrons.
• A double covalent bond is formed when two atoms share two pairs of electrons.
• In a molecule with multiple covalent bonds, the central atom has more than four electron groups around it.
• Non-metal atoms can share electrons with other non-metal atoms to obtain a full outer shell of electrons
• When atoms share pairs of electrons, they form covalent bonds
• Covalent bonds between atoms are very strong
• When two or more atoms are covalently bonded together, they form ‘molecules’
• Covalently bonded substances may consist of small molecules or giant molecules
• Weak intermolecular forces exist between individual molecules
• Shared electrons are called bonding electrons and occur in pairs
• Electrons on the outer shell which are not involved in the covalent bond(s) are called non-bonding electrons
• Simple covalent molecules do not conduct electricity as they do not contain free electrons
• A key difference between covalent bonds and ionic bonds is that in covalent bonds the electrons are shared between the atoms, they are not transferred (donated or gained) and no ions are formed
• There is a strong electrostatic attraction between the shared pair of electrons and the nuclei of the atoms involved in a covalent bond
• In a normal covalent bond, each atom provides one of the electrons in the bond
• A covalent bond is represented by a short straight line between the two atoms, H-H
• Sharing electrons in the covalent bond allows each of the 2 atoms to achieve an electron configuration similar to a noble gas, making each atom more stable
• Simple molecular structures have covalent bonds joining the atoms together, but intermolecular forces that act between neighbouring molecules
• They have low melting and boiling points as there are only weak intermolecular forces acting between the molecules
• As the molecules increase in size, the intermolecular forces also increase as there are more electrons available, causing the melting and boiling points to increase
• The atoms within covalent molecules are held together by covalent bonds while the molecules in a covalent substance are attracted to each other by intermolecular forces
• As the relative molecular mass of a substance increases, the melting and boiling point will increase as well
• An increase in the relative molecular mass of a substance means that there are more electrons in the structure, so there are more intermolecular forces of attraction that need to be overcome when a substance changes state
• The family of organic molecules called alkanes show a clear increase in boiling point as the size of the molecule increases
• Covalent compounds are poor conductors of electricity because there are no free ions or electrons to carry the charge
• Most covalent compounds do not conduct at all in the solid state and are insulators
• Common insulators include the plastic coating around household electrical wiring, rubber, and wood
• When a covalent molecule melts or boils, the covalent bonds do not break, only the intermolecular forces
• Giant covalent structures have a huge number of non-metal atoms bonded to other non-metal atoms via strong covalent bonds
• Giant covalent structures can also be called macromolecules
• Three common macromolecules are diamond, graphite, and C60 fullerene
• Diamond properties:

  • Does not conduct electricity
  • Very high melting point
  • Extremely hard with a density of 3.51 g/cm³
• Silicon(IV) oxide (SiO2) is a giant covalent compound similar to diamond, used to make sandpaper and line the inside of furnaces
• Graphite properties:

  • Conducts electricity and heat
  • Very high melting point
  • Soft, slippery, and less dense than diamond (2.25 g/cm³)
• Fullerenes are carbon allotropes that form hollow tubes or spheres, used for drug delivery systems and as lubricants in industrial processes
• Buckminsterfullerene (C60 fullerene) has 60 carbon atoms forming a hollow sphere shaped like a soccer ball