1.3 Bonding

• What is an ionic bond?

  Oppositelly charged ions held together by electrostatic forces of attraction
• Why do most ionic compounds dissolve in water?

  water molecules are polar so they can attract the positive and negative ions and break up the structure
• Why do ionic compounds conduct electricity and in what state?

  When molten or dissolved in solution as the ions are free to move around
• Why do ionic compounds have high melting points?

  Many strong electrostatic forces of attraction between oppositely charged ions that need lots of energy to overcome
• What is a covalent bond?

  Sharing of outer electrons in order for atoms to obtain a full shell. There is an electrostatic attraction between the shared electron and positive nucleus
• What is a coordinate bond? How is it represented?

  Where one atom donates two electrons to an atom or ion to form a bond. By an arrow
• Describe graphite and its properties

  - each carbon bonded 3 times with 4th electron delocalised

  - layers slide easily as there are weak forces between the layers

  - delocalised electron between the layers allows graphite to conduct electricity as they can carry a charge

  - layers are far apart in comparison to covalent bond length and therefore has a low density

  - lots of strong covalent bonds means graphite has a very high melting point

  - graphite is insoluble as the covalent bonds are to strong to break
• Describe diamond and its structure

  - each carbon bonded 4 times in a tetrahedral shape

  - the tightly packed, rigid arrangement allows heat to conduct well in diamonds

  - very high melting point due to many strong covalent bonds

  - doesn't conduct electricity well as it doesn't have any delocalised electrons
• What are the rules for determining the shape of a molecule?

  1. Use the number of bond pairs and lone hairs of electrons to work out the shape of the molecules

  2. Use the equation:

  Group of element + number of molecules attached to central atom/2

  Answer to first equation - number of molecules attached = lone pairs
• Describe order of repulsion and why this occurs

  BP-BP>BP-LP>LP-LP

  Lone pairs change the shape and bond angles. Lone pairs push bonding pairs closer together. Generally for every lone pair you reduce the shape of the angle by 2.5
• What is the name and bond angle of a shape with 2 BP?

  Linear - 180
• What is the name and bond angle of a shape with 3 BP?

  Trigonal Planar - 120
• What is the name and bond angle of a shape with 4 BP?

  Tetrahedral — 109.5
• What is the name and bond angle of a shape with 5 BP?

  Trigonal Bipyramidal - 90 and 120
• What is the name and bond angle of a shape with 6 BP?

  Octahedral - 90
• What is the name and bond angle of a shape with 3 BP and 1 LP?

  Pyramidal - 107
• What is the name and bond angle of a shape with 2 BP and 2 LP?

  Bent - 104.5
• What is the name and bond angle of a shape with 3 BP and 2 LP?

  Trigonal Planar - 120
• What is the name and bond angle of a shape with 4 BP and 2 LP?

  Square Planar - 90
• What is electronegativity?


  The ability for an atom to attract a pair of electrons towards itself in a covalent bond
• How does electronegativity vary in the periodic table?

  The further up and right you go in the periodic table the more electronegative the element is - fluorine being the most electronegative
• How are polar bonds formed in covalent bonds?

  When there is a difference in electronegativity in the atoms attached due to the uneven distribution of electrons
• How do Van der Waals arise?

  - any molecule or atom with electrons can form a dipole when they move near to another atom or molecule

  - this occurs as electrons in a molecule or atom can move from one end to another hence creating a temporary dipole

  -the delta +ve on one atom or molecule will be attracted to te delta -ve on another and a force of attraction is created

  - this temporary dipole only exists when 2 molecules or atoms are near by. When they move away the dipole interaction is destroyed
• When do permanent dipole-dipole IMF exist?

  In molecules with a polarity
• How do dipole-dipole arise?

  - There are weak electrostatic forces that exist between molecules with a polarity

  - dipole-dipole interactions involves molecules with a permanent dipole and so are stronger

  - the delta +ve on one molecule is attracted to the delta -ve on another

  - molecules that have dipole-dipole also have Van der Waals
• How can you test for polar molecules?


  Polar molecules can be tested by placing a changed rod near a stream of a polar liquid. You should see the liquid bend towards the rod as molecules align to face the oppositely charged rod
• When does hydrogen bonding occur?

  - when you have very electronegative elements

  - hydrogen molecule forms a bond with the lone pair on nitrogen, oxygen or fluorine
• What are metallic bonds?

  - electrostatic attraction between positive metal ions and negative delocalised electrons
• How does number of electrons affect melting point?

  The more electrons an atom can donate to the delocalised system the higher the melting point
• Why are metals good electrical conductors?

  As the delocalised electrons are mobile and can carry current
• Why do metals have a high melting points?


  Due to the strong electrostatic attractions
• Why are metals good thermal conductors?

  As the delocalised electron can transfer kinetic energy
• Describe the solid particle model

  - particles are tightly packed and in a regular arrangement which is why they have a high density

  - particles vibrate on the spot and can be compressed
• Describe the liquid particle model

  - Particles are tightly packed and in a random arrangement which is why they have a high density

  - particles move freely it is very difficult for liquids to be compressed

  - particles in a liquid have more energy than in a solid
• Describe the gas particle model

  - particles are spaced out in a random arrangement which is why they have a low arrangement

  - particles move freely it is relatively easy for gases to be compressed

  - particles in a gas have more energy than in liquids and solids