2012 topic 4.1 bonding - covalent

2012 topic 4.1 bonding - covalent

• 1.
  IB Chemistry PowerPoints Topic 4 Bonding www.pedagogics.ca LECTURE 2 Covalent Bonding
• 3.
  COVALENT BONDING Definition consists of a shared pair of electrons with one electron being supplied by each atom either side of the bond. compare this with dative covalent bonding 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; when one of the elements is in t CCl4, SiCl4 middle of the table; with head-of-the-group elements BeCl2 with high ionisation energies;
• 4.
  COVALENT BONDING -EXCEPTIONS • 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)
• 5.
  HYDROGEN H H Hydrogen atom needs Another hydrogen atom one electron to also needs one electron to complete its outer shell complete its outer shell
• 6.
  HYDROGEN H H atoms share a pair of electrons to form a single covalent bond A hydrogen MOLECULE is formed WAYS TO REPRESENT THE MOLECULE H H H H
• 7.
  HYDROGEN CHLORIDE Cl H Chlorine atom Hydrogen atom also needs one electron needs one electron to complete its to complete its outer outer shell shell
• 8.
  HYDROGEN CHLORIDE Cl H atoms share a pair of electrons to form a single covalent bond WAYS TO REPRESENT THE MOLECULE H Cl H Cl
• 9.
  METHANE WAYS TO REPRESENT H THE MOLECULE Each hydrogen atom needs 1 H H electron to complete its C H outer shell C H H H H H A carbon atom all 4 of4 Carbon shares needs its electrons to form 4 electrons to complete single covalent bonds its outer shell H C H H
• 10.
  AMMONIA WAYS TO REPRESENT THE MOLECULE H Each hydrogen N H atom needs N H one electron to complete its H outer shellH H Nitrogen can only shareelectrons atom needs 3 3 of its H N H 5 to complete its outer shell electrons otherwise it will exceed the maximum of 8 H A LONE PAIR REMAINS
• 11.
  WATER WAYS TOREPRESENT THE MOLECULE Each hydrogen atom needs H one electron to O complete its H O outer shell H H Oxygen atom needs 2 electrons Oxygen can only share 2 of its 6 to complete its outerit will electrons otherwise shell H O exceed the maximum of 8 2 LONE PAIRS REMAIN H
• 12.
  OXYGEN and NITROGEN O O O O each atom needs two electrons each oxygen shares 2 of its to complete its outer shell electrons to form a DOUBLE COVALENT BOND
• 13.
  Orbital theory –bond length and bond strength Covalent bonds are formed when orbitals, each containing one electron, overlap. orbital orbital bonding orbital shape containing 1 containing 1 electron electron The greater the overlap the stronger the bond. The greater the overlap, the shorter the bond length.
• 14.
  Multiple Bonds COMPARE Bondlengths and strengths (data book) 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
• 15.
  Bond Polarity Considera covalent bond between A and B. If A and B have the same electronegativity, the electrons are shared equally. A : B If B is more electronegative than A, the shared electrons have a greater probability of being found closer to B. POLAR COVALENT + A : B -
• 16.
  SIMPLE COVALENT MOLECULES 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
• 17.
  Lewis Structures andbonding – the Chem Prof + - Try NH4 and NO2