C2.2

• Metals


  Elements that react to form positive ions
• Metals


  • Majority of elements are metals
  • Found to the left and towards the bottom of the periodic table
  • They lose electron(s) in order to form positive ions
  • Typically shiny, good electrical conductors, are dense and have high melting points

  
• Non-metals


  Elements that react to form negative ions
• Non-metals


  • Found towards the right and top of the periodic table
  • They gain electron(s) in order to form negative ions
  • Typically dull in appearance, poor electrical conductors, aren't dense and have low melting points

  
• Elements are arranged in order of atomic (proton) number and so that elements with similar properties are in columns, known as groups
• Group number


  Refers to the number of outer shell electrons
• Period number


  Refers to the number of shells of electrons
• Ionic bonding


  • Formed between a metal + non-metal: electrons in the outer shell of the metal atom are transferred to the nonmetal
  • Held together by strong electrostatic forces of attraction between oppositely charged ions
• Ionic compound


  • Sodium chloride (salt): Na+ (small blue particles) and Cl- (larger green ones)
• Ionic compounds


  • Have regular structures (giant ionic lattices) in which there are strong
  • Have high melting and boiling points, because a lot of energy is required to break the many strong bonds
  • When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and carry current
• Covalent bonding


  • Particles are atoms which share pairs of electrons
  • Occurs in most non-metallic elements and in compounds of non-metals
• Covalently bonded substances


  • May consist of small molecules e.g. HCl, H2, O2, Cl2, NH3, CH4
• Substances that consist of simple molecules

  • Usually gases or liquids that have low boiling and melting points
  • Have weak intermolecular forces between the molecules, which are broken in boiling or melting, not the covalent bonds
  • The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points
  • Don't conduct electricity, because simple molecules do not have an overall electric charge
• Giant covalent structures


  • Substances that consist of giant covalent structures are solids with very high melting points
  • All of the atoms in these structures are linked to other atoms by strong covalent bonds, which must be overcome to melt or boil these substances
• Polymers


  • Have very large molecules
  • Atoms in the polymer molecules are linked to other atoms by strong covalent bonds
  • Intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature
• Metallic bonding


  • Metals consist of giant structures of atoms arranged in a regular pattern
  • The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure
  • The sharing of delocalised electrons gives rise to strong metallic bonds
• Metals


  • Have giant structures of atoms with strong metallic bonding, therefore most metals have high melting and boiling points
  • Can conduct heat and electricity because of the delocalised electrons in their structures
  • The layers of atoms in metals are able to slide over each other, so metals can be bent and shaped

  
• Chemical bonding can be explained in terms of electrostatic forces
• Molecules


  Relatively strong and so these substances are solids at room temperature
• Types of substances


  • Metals
• Metallic bonding


  • Metals consist of giant structures of atoms arranged in a regular pattern
  • The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure
  • The sharing of delocalised electrons gives rise to strong metallic bonds
• Metals have giant structures of atoms with strong metallic bonding
• Properties of metals


  • Most metals have high melting and boiling points
  • They can conduct heat and electricity because of the delocalised electrons in their structures
  • The layers of atoms in metals are able to slide over each other, so metals can be bent and shaped
• Ionic bonds


  Electrostatic attraction between oppositely charged ions, formed by the transfer of electrons
• Covalent bonds


  Electrostatic attraction between a shared pair of electrons
• Metallic bonds


  Electrostatic attraction between positive metal ions and the sea of delocalised electrons
• Electron transfer during the formation of an ionic compound can be represented by a dot and cross diagram
• Simple covalent molecules


  • Examples of bonding
• Dot and cross diagrams

  • Shows how atoms are bonded and electrons, but doesn't show the 3D arrangement of molecules

  
• Ball and stick models

  • Show how atoms are bonded and the 3D shape, but doesn't show the electrons or the chemical symbols
• 2D/3D models


  • 2D models don't show the 3D arrangement and 3D models don't give details of bonding or electrons
  • All models do not include intermolecular forces, which are the ones that are broken when boiling and melting simple molecules
• The typical arrangement of electrons in shells from the first shell (closest to nucleus) outwards to the third shell is 2, 8, 8
• The first shell can have up to 2 electrons, the second shell can have up to 8 electrons, and the third shell can have up to 8 electrons
• All atoms will try to acquire the perfect arrangement of 8 electrons in their outer shell, as this is the most stable arrangement
• When metals react, they are losing or gaining electrons to try and achieve the most stable arrangement of outer shell electrons

  
• Mendeleev ordered his periodic table in order of atomic mass, but not always strictly, and left gaps for elements he thought had not been discovered yet
• Elements with properties predicted by Mendeleev were discovered and filled the gaps
• Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct