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• Compounds


  Substances in which 2 or more elements are chemically combined
• Types of strong chemical bonds

  • Ionic
  • Covalent
  • Metallic
• Ionic bonding

  • Particles are oppositely charged ions
  • Occurs in compounds formed from metals combined with non-metals
• Covalent bonding

  • Particles are atoms which share pairs of electrons
  • Occurs in most non-metallic elements and in compounds of non-metals
• Metallic bonding

  • Particles are atoms which share delocalised electrons
  • Occurs in metallic elements and alloys
• Formation of ionic compounds

  1. Metal atoms lose electrons to become positively charged ions

  2. Non-metal atoms gain electrons to become negatively charged ions
• An ion is an atom that has lost or gained electron(s)
• Ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 gain full outer shell of electrons, so they have the same electronic structure as a noble gas (Group 0 element)

  
• Electron transfer during the formation of an ionic compound


  • Dot and cross diagram (e.g. for NaCl)

  
• Covalent bonding

  Atoms share one or more pairs of electrons
• Substances with covalent bonds

  • HCl
  • H2
  • O2
  • Cl2
  • NH3
  • CH4
• Polymers

  Large covalently bonded molecules
• Giant covalent structures (macromolecules)

  Many atoms covalently bonded in a lattice structure
• Examples of giant covalent structures

  • Diamond
  • Silicon dioxide
• Metallic bonding

  Positive ions (atoms that have lost electron(s)) and delocalised electrons arranged in a regular pattern

  
• Delocalised electrons in metallic bonding

  • Free to move through the structure
  • Shared through the structure, making metallic bonds strong
• Ions

  Charged particles that can be single atoms or groups of atoms, formed when electrons are lost or gained
• Metal atoms lose electrons to form positive ions, non-metal atoms gain electrons to form negative ions
• Stable electronic structure

  Having a full outer shell of electrons, like a noble gas
• Periodic table group number and ionic charge

  • Group 1 elements form 1+ ions
  • Group 2 elements form 2+ ions
  • Group 6 elements form 2- ions
  • Group 7 elements form 1- ions
• Ionic bonding

  When metals react with non-metals, electrons are transferred from the metal atoms to the non-metal atoms, forming oppositely charged ions that are strongly attracted to each other
• Dot and cross diagrams

  Used to show what happens during ionic bonding, with electrons represented by dots and crosses
• Giant ionic lattice

  The structure of ionic compounds, a closely-packed regular arrangement of oppositely charged ions held together by strong electrostatic forces
• Representations of ionic compounds

  • Dot and cross diagrams
  • 3D models
  • Ball and stick models
• Working out the formula of an ionic compound

  1. From a dot and cross diagram: count the atoms of each element

  2. From a 3D or ball and stick model: identify the ions and balance the charges
• Properties of ionic compounds

  • High melting and boiling points due to strong electrostatic attraction
  • Most dissolve easily in water
• Ionic compounds have high melting and boiling points, and most dissolve easily in water
• Electrical conductivity


  Ionic compounds don't conduct electricity when solid because the ions are all held in fixed positions. However, when they're melted or dissolved, the ions are free to move and they'll carry electric charge.
• Dissolving in water


  Free ions
• Covalent Bonding


  Atoms sharing their electrons
• Covalent bond


  A pair of electrons is shared between two atoms. Atoms share electrons with each other to get full outer shells (highest energy levels). They only share electrons in their outer shells and both atoms involved in the bond end up with one extra electron in their outer shell. The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong.
• Single covalent bond


  Provides one extra shared electron for each atom
• Covalent bonds


  • Occur between non-metal atoms, either in non-metallic elements or in compounds of non-metals
• Representing covalent bonding


  • Dot and cross diagrams
  • Displayed formulas
  • 3D models and ball and stick models
• Dot and cross diagrams


  The shared electrons can be drawn in the overlap between the outer orbitals of the two atoms
• Displayed formulas


  Show the covalent bonds as single lines between atoms
• 3D models and ball and stick models


  Show the atoms and their arrangement in space
• Finding molecular formulas


  Count up how many atoms of each element there are in a diagram of the molecule
• Simple molecules


  • Made up of only a few atoms joined by covalent bonds
• Chlorine


  Chlorine atoms need one more electron to gain a stable electronic structure. So, two chlorine atoms each share one of their electrons to form a chlorine molecule containing one shared pair of electrons - a single covalent bond.