Electronegativity (Carbon dioxide (Carbon dioxide is a non-polar…
Carbon dioxide is a non-polar molecule
The 2 C=O bonds each have a permanent dipole
The 2 dipoles act in opposite directions and exeactly oppose one another
Over the whole molecule, the dipoles cancel and ther overall dipole is 0.
Simple molecular substances
A simple molecular substance is made up of simple molecules, small units containing a definite number of atoms with a definite molecular, such as a neon, Ne, hydrogen, H2, water, H2O and carbon dioxide CO2
They form a simple molecular lattice when they are solid. The molecules are held together by weak intermolecular forces while the atoms are held together by strong covalent bonds.
They have have a low melting point and low boiling point because the intermolecular are weak so are easily broken. However the covalent bonds are strong so are not broken.
Induced dipole dipole interactions
Induced dipole-dipole attractions occur all molecules
The more electrons there are the stronger the induced dipole attractions are.
They are the weakest intermolecular force but when there are enough of them they an be stronger than hydrogen bonds
Permanent dipole-dipole interactions
Can only occur between polar molecules like H—Cl
Extra energy is needed to break the additional permanent attractions. This increases the boiling and melting points of polar molecules
Making them the second strongest intermolecular forces
The strongest of the intermolecular forces can only occur between nitrogen and hydrogen, fluorine and hydrogen, oxygen and hydrogen. Because the electronegativity is large enough to allow them to occur.
Hydrocarbon liquids such as hexane C6H14 are non-polar solvents and do not mix with water
If the bonding atoms are of the same element then the bond is pure covalent as the electrons are shared equally
In a non-polar bond the bonded electron pair is equally shared between the bonded atoms. A bond will be non-polar when the bonded atoms are the same or the bonded atoms have a similar electronegativity
Hydrogen chloride (H—Cl) is a good example as hydrogen has an electronegativity of 2.1 while chlorine has an electronegativity of 3 this is a large enough difference for it to be polar. The chlorine atom is more electronegative so has a greater effect on the bonded pair of electrons resulting in a slightly negative charge on the chlorine and a positive charge on the hydrogen :
The partial positive charge is represented by a §+
The partial negative charge is represented by a §-
In a polar bond the electron pair is shared unequally between the bonded atoms. A bond will be polar when the bonded atoms have different electronegativity
A water (H2O) molecule is polar. The 2 O—H bonds each have a permanent dipole
The 2 dipoles act in different directions but do not oppose each other making it polar
Overall the oxygen end of the molecule has a §- charge and the hydrogen end of the molecule has a §+ charge
Polar solvents and solubility
The ionic lattice of NaCl dissolves in water because the attraction between the Na+ and O- and the attraction between the Cl- and H+ is stonger than the bonds attractions between the Na+ and Cl-
If the electronegativity is greater than 1.8 they type of bond is ionic
Non metals like nitrogen, oxygen and chlorine are all very electronegative
If the electronegativity is between 0 and 1.8 the type of bond is polar covalent
If the electronegativity difference is 0 then the type of bond is covalent
Group 1 metals like lithium, sodium and potassium are the least electronegative atoms
The Pauling scale is used to measure electronegativity. Fluorine being the most electronegative and potassium being the least electronegative.