Bonding and Types of Substance

• Ions


  Charged particles formed when atoms lose or gain electrons
• Ionic bonds


  • Forces of attraction that hold atoms together when bonds form
  • Energy is released from the atoms, making them more stable
  • Less reactive
• Noble gases


  Atoms with a full outer electron shell, the most stable atoms
• Formation of sodium chloride

  1. Sodium atom loses electron

  2. Chlorine atom gains electron

  3. Ions form

  4. Ionic bond forms
• Dot and cross diagrams can be used to show what happens when ions are formed
• Cations


  Positive ions formed when metal atoms lose electrons
• Anions


  Negative ions formed when non-metal atoms gain electrons
• Electrostatic forces


  Forces of attraction between oppositely charged objects that hold ions together in an ionic bond
• Atoms that easily form ions will have either a nearly full or a nearly empty outer electron shell
• Ion formation in groups 1, 2, 6 and 7

  • Group 1: 1 electron lost, 1+ charge
  • Group 2: 2 electrons lost, 2+ charge
  • Group 6: 2 electrons gained, 2- charge
  • Group 7: 1 electron gained, 1- charge
• Formation of magnesium oxide ionic bond

  1. Magnesium atom loses 2 electrons

  2. Oxygen atom gains 2 electrons

  3. Ionic bond forms
• Aluminium atom loses 3 electrons when its ion is formed
• Bromine is in group 7 of the periodic table
• Bromide ion has the same number of electrons as a bromine atom
• Bromide ion


  Bromine atom that has gained 1 electron
• Hydrogen ion (H+) is just a proton
• Potassium (K) in group 1 forms a 1+ ion
• Selenium (Se) in group 6 forms a 2- ion
• Sulfur atom contains 16 protons
• Sulfur atom forms S2- ions
• Ionic lattice


  Regular repeating arrangement of oppositely charged ions held together by strong electrostatic forces
• Ionic compounds form crystals due to their regular lattice structure
• There are seven basic crystal structures
• Ionic compounds are electrically neutral, with the same number of positive and negative charges
• Working out ionic formulae


  Use ion charges to determine the number of each ion needed for electrical neutrality
• Polyatomic ions are groups of two or more atoms that have become charged
• Compound names ending in -ate contain oxygen
• Compound names ending in -ide do not contain oxygen
• Ionic compounds contain ions, not atoms or molecules
• Strong electrostatic forces of attraction between oppositely charged ions


  Require high energy to overcome, resulting in high melting and boiling points
• Highly charged ions (e.g. Mg2+) attract other ions more strongly, increasing melting point
• Ionic compounds conduct electricity when molten or in aqueous solution, but not in solid state
• Anode


  Positive electrode that attracts negative ions (anions)
• Cathode


  Negative electrode that attracts positive ions (cations)
• It is the movement of ions that enables ionic compounds to conduct electricity, not electrons
• Magnesium oxide is insoluble in water
• Covalent bonds


  Strong bonds formed by the sharing of pairs of electrons between atoms
• Molecular substances contain groups of atoms that are held together by strong bonds called covalent bonds
• Molecular formula


  Shows the number of atoms of each element in a molecule
• Molecular formulae


  • CHNO
  • CHMO
  • HO
  • CHO