3.1.3 Bonding

• Covalent bonding: When two atoms share pairs of electrons
• A dative covalent bond forms when the shared pair of electrons in the covalent bond comes from only one of the bonding atoms.
• Metallic bonding: the electrostatic force of attraction between positive metal ions and delocalised electrons
• What are the 3 main factors affecting the strength of metallic bonding?

  1. Nuclear Charge
  2. Number of Delocalised Electrons per atom
  3. Size of Ion
• What structure do ionic structures take? Giant Ionic Lattice
• What are the properties of ionic compounds?

  • They are usually crystalline solids.
  • They have high melting points and boiling points.
  • They are usually soluble in water
  • They conduct electricity when dissolved in water or when melted
• Explain 3 key properties of metals

  • High melting points due to strong metallic bonds in giant metallic structures, these are hard to break
  • Good conductors of electricity because delocalised electrons can move through the structure and carry a charge
  • Malleable because layers of ions can slide over each other, held together by electrostatic forces
• Describe properties of simple molecules

  • Low boiling / melting points  - due to weak intermolecular forces between molecules
  • Poor conductivity because there aren't any ions + electrons are localised
• Linear:

  • b.p = 2
  • l.p = 0
  • bond angle = 180
  • example = CO2 BeF2

  
• Trigonal Planar

  • b.p = 3
  • l.p = 0
  • bond angle = 120
  • example = BF3 , AlCl3

  
• Tetrahedrall:

  • b.p = 0
  • b.p = 4
  • bond angle = 109.5 
• Trigonal Bipyramidal:

  • b.p = 5
  • l.p = 0
  • b.a = 90 and 120
• Trigonal Pyramida:

  b.p = 3

  l.p = 1

  b.a = 107

  
• Bent

  • b.p = 2
  • l.p = 2
  • b.a = 104.5
  • examples = H20, SCl2

  
• What shape is formed from 4 bp and 1 lp? see-saw
• What shape is formed from 3 b.p and 2 l.p? T shape
• What shape is formed from 3 l.p and 2 b.p? Linear
• What shape is made from 4 bond pairs and 2 lone pairs? Square Planar
• Electronegativity: the power of an atom to attract bonded electrons in a covalent bond towards itself
• FONCI are the most electronegative atoms
• Electronegativity is measured on the Pauling scale, ranging from 0 to 4
• Electronegativity will increase across a period as the number of protons increases but there is similar shielding.
• Electronegativity will decrease down a group because the distance between the nucleus and bonded electrons increase and the shielding of the inner shell electrons increases.
• Dipole moment: The overall effect of polarity of the bonds in a molecule
• Describe van der Waals’ forces of attraction:

  • Temporary dipoles are created by the random movement of electrons
  • → induces dipole in neighbouring molecule
  • → temporary induced dipole-dipole attraction aka van der Waals forces of attraction
• What factors lead to stronger Van Der Waals forces?

  • More electrons
  • Bigger surface area
• The boiling point of halogens down group 7 increases because there are more electrons in bigger molecules .
• Long chain alkanes have a higher b.p than spherical shaped alkanes because ...

  
  

  There is a larger surface area of contact between chained molecules than there is spherical molecules.
• Describe permanent dipole-dipole forces:

  • Electrostatic forces between polar molecules
  • Stronger than Van der Waals so compounds have higher boiling point
• What is hydrogen bonding? The strongest type of intermolecular force that forms between Hydrogen and F, O, N. The lone pair on these atoms attract a hydrogen atom on another molecule.
• 3 types of intermolecular forces:

  1. Van Der Waals
  2. Dipole-Dipole
  3. Hydrogen Bonds
• What are the 4 types of crystal structures?

  1. Ionic
  2. Metallic
  3. Simple Molecular
  4. Giant Covalent
• Describe the properties of simple molecular compounds

  1. low melting point because of weak intermolecular forces
  2. poor solubility in water
  3. poor conducitivity of electricity in solid/when molten as there are no ions / electrons are localised
  4. generally mostly gases and liquids
• State 5 properties of metals

  • high mp/bp due to strong attraction between +ve ions and sea of delocalised electrons
  • insoluble
  • good conductors of electricity
  • shiny
  • malleable, as layers of ions can slide over each other
• Solid: 

  • Arrangement: Tightly packed in a regular arrangement
  • Movement: Vibrate in fixed positions
• Liquid:

  • Arrangement: Tightly packed in a random arrangement
  • Movement: Particles move freely and have more energy than in a solid
• Gases:

  1. Arrangement: Spaced out and in a random arrangement
  2. Movement: Particles move freely and have lots of energy
• Graphite is soft because the structure is in planes/layers and weak bonds between planes mean they can slide
• Electronegativity: The power of an atom or nucleus to withdraw or attract a pair of electrons in a covalent bond
• The melting point of carbon is high because:

  • the macromolecular structure is giant.
  • Covalent bonds in the structure are strong
  • and require lots of energy to break