Modelling molecules

• What is a covalent bond?

  A covalent bond is a shared pair of electrons.
• What do covalent bonds form?

  Covalent bonding forms molecules.
• What are the properties of substances with small molecules?

  They have low melting and boiling points, and do not conduct electricity.
• What is a dot and cross diagram used for?

  • To show the bonding in a small molecule
  • Dots represent electrons from one atom
  • Crosses represent electrons from another atom
• How is a covalent bond represented in a dot and cross diagram?

  The outer shell of each atom is drawn as a circle, and overlapping circles indicate a covalent bond.
• What forms when two hydrogen atoms share their outer electron?

  A hydrogen molecule, H₂, forms.
• What is the structural formula of a molecule?

  A structural formula shows the bonds between the atoms in a molecule.
• How is each atom represented in a structural formula?

  Each atom is shown by its chemical symbol.
• How are covalent bonds represented in a structural formula?

  Each covalent bond is shown as a straight line.
• How many covalent bonds does an ammonia molecule have?

  An ammonia molecule has three covalent bonds.
• What is a three-dimensional ball and stick model used for?

  • To show the structure of a small molecule
  • Illustrates how atoms and bonds are arranged in space
• What is one advantage of using a dot and cross diagram?

  A dot and cross diagram shows the pairs of outer electrons and which atoms they have come from.
• What is one limitation of using a dot and cross diagram?

  It does not show how the atoms are arranged in space.
• What is one advantage of using a structural formula?

  The structural formula shows the bonds between the atoms.
• What is one limitation of using a structural formula?

  It does not show which atoms the electrons in the bonds have come from.