Bonding and Structure

• 4.2.1.1 Chemical Bonds


  three types of strong chemical bonds: ionic, covalent and metallic.
• Ionic bonding


  particles are oppositely charged. Between non-metals and metals.
• covalent bonding


  particles are atoms which share pairs of electrons. Between non-metals
• Metallic bonding


  particles are atoms that share delocalised electrons. Between metals and alloys.
• Transfer of electrons


  ionic bonding. when non-metal and metal react the metal loses their electron(s) to form a positive charged ion and the non-metal gains the electron(s) to produce a negative charged electron.
• 4.2.1.2 Ionic bonding


  When a metal reacts with a non-metal electrons from the metals outer shell transfers to the non-metal. Metal atoms lose their electrons to become a positively charged ion and the non-metal atom gain their electrons to become a negatively charged ion. Ions are produced by group 1 and 2 metals and group 6 and 7 non-metals to create the structure of noble gases

  (Group 0). The electronic transfer during the formation of an ionic compound can be represented through a dot and cross diagram
• ionic compound dot and cross diagram

  the charges of the ions produced are related to their group number of the element in the periodic table.

  
• 4.2.1..3 Ionic compounds


  Giant structure of ions which are held together by strong electrostatic forces of attraction between oppositely charged ions. Forces act in all directions in the lattice. (Ionic bonding)

  
• Limitations of dot and cross diagrams


  they don't show the structure of the compound, the size of the ions or how they are arranged.
• Limitations of the structural formula

  do not show which atoms the electrons have come from.
• limitations of a ball and stick diagram

  isn't to scale so size of ions not shown. aren't any gaps between ions.
• limitations of 3D model

  only shows you the outside of the ionic compound and isn't to scale.
• structure of sodium chloride

  Giant ionic lattice

  
• 4.2.1.4 Covalent Bonding


  when atoms share pairs of electrons they form covalent bonds. May consist of small molecules. Some covalent bonded substances have large molecules, e.g. polymers. Some have giant covalent structures e.g. diamond and silicon dioxide.
• Polymers can be represented as

  where the n is a large number

  
• hydrogen chloride

  
• water (H20)

  
• ammonia


  NH3

  
• methane


  CH4

  
• 4.2.1.5 Metallic bonding


  Consist of giant structures of atoms arranged in a regular pattern. Electrons in outer shell of metal atoms are delocalised so free to move through the whole structure. Sharing of delocalised electrons gives rise to strong metal bonds.

  
• 4.2.2 How bonding and structure are related to the properties of substances
• 4.2.2.1 Three states of matter

  Solid, liquid and gas. Melting and freezing take at melting points, boiling and condensing takes place at the boiling point.
• changing states


  amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance. The nature of the particles involved depends on type of bonding and structure of the substance. Stronger the forces between particles the higher the boiling and melting points.
• 4.2.2.2 State symbols


  gas (g), Liquid (l), solid (s), aqueous (aq)
• 4.2.2.3 Properties of ionic compounds


  Have regular structures (giant ionic lattices) in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions. Compounds have high melting and boiling points because of large amounts of energy needed to break many strong bonds. When melted or dissolved in water, ionic compounds conduct electricity because ions are free to move and so charge can flow.
• 4.2.2.4 properties of small molecules

  Usually gases or liquids that have relatively low melting and boiling points. Have only weak intermolecular forces. These intermolecular forces are overcome when substance melts or boils NOT the covalent bonds. intermolecular forces INCREASE with size of molecule so larger molecules have higher melting and boiling points. Substances do NOT conduct electricity because molecules do NOT have an overall electric charge.
• properties of small molecular substances

  low melting and boiling points due to weak intermolecular bonds. They do NOT conduct electricity due to not having an overall electric charge.
• Polymers


  Have very large molecules. Atoms are linked t other atoms by strong covalent bonds. The intermolecular forces between polymer molecules are relatively strong so these substances are solids at room temp.
• 4.2.2.6 Giant Covalent Structures

  Are solids with very high melting point. All atoms are linked to other atoms by strong covalent bonds. Bonds must be overcome to melt or boil substances. Diamond and graphite (forms of carbon) and silica examples.
• 4.2.2.7 Properties of metals and alloys

  Metals have giant structures of atoms with strong metallic bonding. This means that most metals have high melting and boiling points. In pure metals, atoms arranged in layers, allows metals to be bent (malleable) and shaped. Pure metals are too soft for most uses so are mixed together with other metals to make alloys which are harder.
• Why alloys are harder than pure metals

  The regular layers in pure metal are distorted by atoms of different sizes in an alloy
• 4.2.2.8 Metals as conductors


  good conductors of electricity due to delocalised electrons to carry electrical charge through metal. Good conductors of thermal energy because energy is transferred by delocalised electrons.
• 4.2.3 Structure and bonding of carbon
• 4.2.3.1 Diamond


  Each carbon atom forms four covalent bonds with other carbon atoms in giant covalent structure. very hard, has very high melting point aand does NOT conduct electricity.

  
• Properties of diamond


  hard, crystal structure, tightly bonded
• 4.2.3.2 Graphite


  Each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have NO covalent bonds between the layers. One electron from each carbon atom is delocalised. It is similar to metals as it has one delocalised electron.

  
• properties of graphite


  slippery, layered structure, bonds in layers are tight but between layers are weak and conducts electricity.
• 4.2.3.3 Graphene and fullerines

  Graphene single layer of graphite and has properties that make it useful for electronics and composites
• properties of graphene


  - Conductor of thermal energy and electricity

  - LOW density

  - It is theMOST REACTIVEform of carbon

  - Pieces are incredibly strong for their mass

  
• Fullerines


  molecules of carbon atoms with hollow shapes. Structure based of hexagonal rings of carbon atoms but may also contain five or seven carbon atoms. First fullerine Buckminsterfullerine (C60) has spherical shape.