Unit 3 Bonding

• Compounds are atoms of different elements bonded together
• Two main types of compounds

  Ionic

  Covalent
• Ionic bonding is when ions are held together by electrostatic attraction
• Ions are formed when one or more electrons are transferred from one atom to another
• Electrostatic attraction hold positive and negative ions together - it is very strong
• Ionic crystals are giant lattices of ion and is a regular structure
• Ionic compounds conduct electricity when they are molten or dissolved but not when they are solids
• Ionic compounds have high melting points
• Ionic compounds tend to dissolve in water
• Molecules are groups of atoms bonded together
• Molecules are held together by strong covalent bonds
• A single covalent bond contains a shared pair of electrons
• Some molecule have double or triple bonds meaning they have multiple shared pairs of electrons
• Giant covalent structure have a huge network of covalently bonded atoms sometimes called macromolecular structure
• Two types of giant covalent carbon structure

  Graphite - sheets of hexagons with delocalised electrons

  Diamond - arranged in tetrahedral shaped
• Dative covalent bonding is where both electrons come from one atom
• Molecular shape depends on electron pairs around the central atoms
• Electron pairs exist as part of charge clouds
• Electron charge clouds repel each other
• Total number of electron pair : 2

  Number of bonding pairs: 2

  Number of lone pairs: 0

  Shape name: Linear

  Shape angle: 180

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• Total number of electron pair : 3

  Number of bonding pairs: 3

  Number of lone pairs: 0

  Shape name: Trigonal planar

  Shape angle: 120

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• Total number of electron pair : 3

  Number of bonding pairs: 2

  Number of lone pairs: 1

  Shape name: bent

  Shape angle: 118

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• Total number of electron pair : 4

  Number of bonding pairs: 4

  Number of lone pairs: 0

  Shape name: Tetrahedral

  Shape angle: 109.5

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• Total number of electron pair : 4

  Number of bonding pairs: 3

  Number of lone pairs: 1

  Shape name: Trigonal pyramidal

  Shape angle: 107

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• Total number of electron pair : 4

  Number of bonding pairs: 2

  Number of lone pairs: 2

  Shape name: Bent

  Shape angle: 104.5

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• Total number of electron pair : 5

  Number of bonding pairs: 5

  Number of lone pairs: 0

  Shape name: Trigonal bipyramidal

  Shape angle: 90 and 120

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• Total number of electron pair : 5

  Number of bonding pairs: 4

  Number of lone pairs: 1

  Shape name: See saw

  Shape angle: 89 and 119

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• Total number of electron pair : 5

  Number of bonding pairs: 3

  Number of lone pairs: 2

  Shape name: T shape

  Shape angle: 89 and 120

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• Total number of electron pair : 6

  Number of bonding pairs: 6

  Number of lone pairs: 0

  Shape name: Octahedral

  Shape angle: 90

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• Total number of electron pair : 6

  Number of bonding pairs: 5

  Number of lone pairs: 1

  Shape name: Square pyramid

  Shape angle: 89

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• Total number of electron pair : 6

  Number of bonding pairs: 4

  Number of lone pairs: 2

  Shape name: Square planar

  Shape angle: 90

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• Some atoms attract bonding electrons more than other atoms
• Fluorine is the most electronegative element
• As you go up and right across the periodic table the elements get more electronegative. With the strongest being fluorine at 4
• Hydrogen bonding only happens when hydrogen is covalently bonded to fluorine, nitrogen or oxygen
• Substances with hydrogen bonds have higher boiling and melting points than other similar molecules because they need extra energy to break hydrogen bonds
• As liquid water cools to form ice the molecules make more hydrogen bonds and arrange themselves in regular lattice structure
• The positive metal ions are attracted to the delocalised negative electrons. They form a lattice of closely packed positive ions in a sea of delocalised electrons this is a metallic bond
• Metals have high melting points because of strong electrostatic attraction between positive metal ions and a sea of delocalised electrons
• Delocalised electrons can pass kinetic energy to each other and make good thermal conductors