1. Y12 Chemistry

2.   Having poles  Opposite ends  In molecules its respect to charge  Covalent bonds can be either polar or non-polar Polarity

3.  Electronegativity The ability of an atom to attract bonding electrons to itself

4.   Every atom is neutral….  But the positive nucleus attracts bonding electrons depending on;  The amount of positive charge on the nucleus of the atom  The radius of the atom Electronegativity

5.  Electronegativities 2.1 H 1.0 Li 1.5 Be 2.0 B 2.5 C 3.0 N 3.5 O 4.0 F 0.9 Na 1.2 Mg 1.5 Al 1.8 Si 2.1 P 2.5 S 3.0 Cl 0.8 K 1.0 Ca Increase across a period Increase up a group Flourine has the highest electronegativity

6.  Polar Bonds

7.   Calculating the electronegativity difference between two atoms will tell us if a bond is ionic, polar covalent or non polar covalent. Ionic Covalent Continuum 1.6 Ionic Polar covalentNon polar covalent

8.   A bond which has a positive end and a negative end is said to have an electrical dipole  The direction of the dipole is from positive to negative Dipoles

9.   Many molecules contain more than one bond  Each bond may or may not be polar  Sometimes the dipoles will be balanced and sometimes they will form a net dipole in one direction  A molecule with a net dipole is a polar molecule Polar molecules

10.   Molecules with one bond are easy  If the bond is polar the molecule is polar Predicting polarity

11.   In molecules with more than two atoms and polar bonds, the molecule will be non-polar only if the polarities of the bonds cancel each other out Predicting Polarity C C O O O O CO 2 is non polar because the shape is symmetrical so the polar bonds cancel each other out

12.  Predicting Polarity Identify all bonds which are polar Establish the shape / symmetry of the molecule Decide whether the polarities will cancel

13.  Symmetrical shapes LinearTrigonal planarTetrahedral Unsymmetrical shapes Bent Trigonal pyramid Symmetry of shapes

14.   4 C – Cl bonds  All C  Cl CCl 4 Shape is symmetrical Polar bonds cancel Non - polar

15.   3 C – Cl bonds and 1 C - H  3 C  Cl and 1 C  H CHCl 3 Shape is symmetrical Polar bonds do not cancel out polar

16.   3 N – H bonds  All N  H NH 3 Shape is unsymmetrical Dipoles do not cancel out polar

17. Polar Bonds Non-polar bonds Bonded non-metal atoms identical Bonded non-metal atoms different Electronegativity difference No electronegativity difference Polar molecule Non-polar molecule Net dipole Polar bonds cancel Polar bonds don’t cancel Polar bonds asymmetrically arranged Polar bonds symmetrically arranged Construct a flow-chart to identify polar molecules using the following statements:

18. Bonded non-metal atoms identical Bonded non-metal atoms different No electronegativity difference Non-polar bonds Electronegativity difference Polar Bonds Polar bonds symmetrically arranged Polar bonds cancel Non-polar molecule Polar bonds asymmetrically arranged Polar bonds don’t cancel Net dipole Polar molecule