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2016 topic 4.2 bonding - covalent

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IB Chemistry Bonding Topic 4

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2016 topic 4.2 bonding - covalent

  1. 1. LECTURE 2 Covalent Bonding IB Chemistry Power Points Topic 4 Bonding www.pedagogics.ca
  2. 2. Definition a shared pair of electrons generally with one electron being supplied by each atom either side of the bond. atoms are held together because their nuclei which have an overall positive charge are attracted to the shared electrons Formation between atoms of the same element N2, O2, diamond, graphite between atoms of different elements CO2, SO2 on the RHS of the table; BETWEEN NON-METALS when one of the elements is in CCl4, SiCl4 the middle of the table; with head-of-the-group elements BeCl2 with high ionisation energies; COVALENT BONDING + +
  3. 3. HYDROGEN Another hydrogen atom also needs one electron to complete its outer shell Hydrogen atom needs one electron to complete its outer shell HH
  4. 4. HYDROGEN H H atoms share a pair of electrons to form a single covalent bond A hydrogen MOLECULE is formed H H HH WAYS TO REPRESENT A MOLECULE of H2
  5. 5. METHANE C Each hydrogen atom needs 1 electron to complete its outer shell A carbon atom needs 4 electrons to complete its outer shell H H H H
  6. 6. METHANE Carbon shares all 4 of its electrons to form 4 single covalent bonds
  7. 7. METHANE Carbon shares all 4 of its electrons to form 4 single covalent bonds H C H H H H C H H H WAYS TO REPRESENT THE MOLECULE
  8. 8. AMMONIA NEach hydrogen atom needs one electron to complete its outer shell Nitrogen atom needs 3 electrons to complete its outer shell Nitrogen can only share 3 of its 5 electrons otherwise it will exceed the maximum of 8 A LONE PAIR REMAINS H H H H N H H H N H H WAYS TO REPRESENT THE MOLECULE
  9. 9. WATER O Each hydrogen atom needs one electron to complete its outer shell Oxygen atom needs 2 electrons to complete its outer shell Oxygen can only share 2 of its 6 electrons otherwise it will exceed the maximum of 8 2 LONE PAIRS REMAIN H H H O H H O H WAYS TO REPRESENT THE MOLECULE
  10. 10. OXYGEN O each atom needs two electrons to complete its outer shell each oxygen shares 2 of its electrons to form a DOUBLE COVALENT BOND O O O and NITROGEN
  11. 11. Orbital theory – bond length and bond strength Covalent bonds are formed when orbitals, each containing one electron, overlap. The greater the overlap the stronger the bond. The greater the overlap, the shorter the bond length. less overlapping orbitals Single < Double < Triple more overlapping orbitals orbital containing 1 electron orbital containing 1 electron bonding orbital shape
  12. 12. COMPARE Bond lengths and strengths (data booklet has all the values) O – O 0.148 146 O = O 0.121 496 C – C 0.154 348 C = C 0.134 612 C ≡ C 0.120 837 C – O 0.143 360 C = O 0.122 743 Multiple Bonds
  13. 13. Bond Polarity A : B Consider a covalent bond between A and B. If A and B have the same electronegativity, the electrons are shared equally. If B is more electronegative than A, the shared electrons have a greater probability of being found closer to B. POLAR COVALENT + A : B - 
  14. 14. HYDROGEN CHLORIDE Cl H Hydrogen atom also needs one electron to complete its outer shell Chlorine atom needs one electron to complete its outer shell
  15. 15. HYDROGEN CHLORIDE Cl H atoms share a pair of electrons to form a single covalent bond H ClH Cl WAYS TO REPRESENT THE MOLECULE
  16. 16. Bonding Atoms are joined together within the molecule by covalent bonds. Electrical Don’t conduct electricity as they have no mobile ions or electrons Solubility Tend to be more soluble in organic solvents than in water; some are hydrolysed Boiling point Low - compared to ionic compounds intermolecular forces are weak; they increase as molecules get a larger surface area e.g. CH4 -161°C C2H6 - 88°C C3H8 -42°C as the intermolecular forces are weak, little energy is required to to separate molecules from each other so boiling points are low some boiling points are higher than expected for a given mass because you can get additional forces of attraction these concepts will be clarified and expanded on in later lessons SIMPLE COVALENT MOLECULES
  17. 17. Try NH4 + and NO2 - Lewis Structures and bonding – the Chem Prof
  18. 18. • atoms share electrons to get the nearest noble gas electronic configuration NOT ALWAYS • some don’t achieve an “octet” as they haven’t got enough electrons ex Al in AlCl3 (why is this a covalent bond?) • others share only some - if they share all they will exceed their “octet” ex NH3 and H2O • atoms of elements in the 3rd period onwards can exceed their “octet” if they wish as they are not restricted to eight electrons in their “outer shell” ex PCl5 and SF6 (HL only) COVALENT BONDING - EXCEPTIONS

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