Topic 2 - Chemical Bonding and Structure

• The number of delocalised electrons per cation in metals determine the melting point
• Metals can conduct electricity because:

  • Delocalised electrons pass kinetic energy
  • Cations are closely packed and can pass energy
• The smaller the ions, the stronger the ionic bond because the ions are more closely packed
• Ions with a higher charge, have a stronger ionic bond as they will be more attracted to eachother
• The smaller the ionic radius, the stronger the bond
• Ionic compounds are often brittle and water soluble
• Ionic compounds are brittle because when layers slide across, same charge ions are against eachother and repel
• There are two types of covalent bonds: pi and sigma
• Sigma bonds form from the end on overlap of two s orbitals or the ends of p orbitals
• Pi bonds form at the sideways overlap of two p orbitals
• Pi bonds can only form if a sigma bond is already there
• Pi bonds are weaker because there is less overlap of the electron cloud
• Double-bonded molecules are more reactive because pi bonds cause there to be a significantly higher electron density above and below the bond
• Generally, the shorter the bond, the stronger
• Electronegativity is the ability of an atom to attract a bonding pair of electrons
• Polar bonds happen when there is a difference in electronegativity between two atoms
• If a molecule has symmetrical polar bonds, the charges can equal out, making the molecule overall neutral
• A molecule is only polar when the charges of polar bonds is asymmetrical
• Discrete molecules are electrically neutral
• Some atoms may expand their octet to above 8 electrons
• Some atoms will keep less than 8 electrons in their outer shell, they are electron deficient
• Dative covalent bonds are represented by an arrow pointing to the empty orbital
• The shape of a molecule is a result of electron repulsion
• lone pair-lone pair repulsion is the strongest repulsion
• 2 bonding pairs, no lone pairs is linear
• Linear have a bond angle of 180
• 2 bonding pairs and 2 lone pairs is V shaped
• V-shaped have a bond angle of 104.5
• 3 bonding pairs and no lone pairs is trigonal planar
• Trigonal planar have a bond angle of 120
• 3 bonding pairs and 1 lone pair is trigonal pyramidal
• Trigonal pyramidal has a bond angle of 107
• 4 bonding pairs and no lone pairs is tetrahedral
• Tetrahedral has a bond angle of 109.5
• 5 bonding pairs and no lone pairs is trigonal bipyramidal
• Trigonal bipyramidal has a bond angle of 90 and 120
• 6 bonding pairs and no lone pairs is octahedral
• Trigonal Planar

  
• Tetrahedral

  
• Trigonal bipyramidal