I.M. FORCES OF ATTRACTION Flashcards
Polar molecule’s FOA
Van der Waal and dipole dipole
Polar molecules containing N/O/F-H bonds
Van der Waals, Hydrogen bonds, dipole dipole
Unsymmetrical molecules/ polar diatomic molecules (HBr)
Van der Waals, dipole dipole
Non polar symetrical molecules/ diatomic molecules (Cl2)
Van der Waals
Factors that determine the electronegativity value of an element
-The size of the nuclear charge
-The size of the atom
(as nuclear charge inceases, there will be an increased attarction between nuclear charge and the pair of electrons in a covalent bond :. electronegativity increases
As the size of the atom increases…
The pair of electrons in the covalent bond will be further away from the nucleus and there will be a decreased attraction from the nuclear charge :. electronegativity increases. There will also be a shielding effect of the inner electrons
Going across a period electronegativity…
Increases as the nuclear charge increases and the size of the atoms decreases therefore there will be a greater attraction between the nucleus and the pair of electrons in the covalent bond
Going down a group electronegativity…
Decreases as the effect of the increase in nuclear charge is less than the effect of increase in atomic radius and the shielding effect of the inner electrons, there will be less attraction between the nucleus and the pair of electrons in the covalent bond
Covalent character
Occurs when atoms in a bond have very similar electronegativities therefore resulting in bonds which have a lot of covalent character and are non-polar
Criteria for the molecule to be NON-POLAR
-No lone pairs
-All the terminal atoms are identical
(symmetrical molecules, all the dipoles cancel out therefore non-polar)
POLAR molecules explanation
The dipoles do not cancel out (unsymmetrical) therefore the molecule is polar
Iodine exists as a grey-black solid. Describe the bonding in and the structure of iodine crystals and the relative solubilities in water and hexane
Iodine is a simple molecular covalent diatomic molecule which is non-polar. As it is non-polar it only has weak vdw attractions between molecules, which require little heat to break :. sublimes (to a purple vapour) upon heating. As iodine is non-polar it will be ore soluble in a non-polar solvent like hexane and less soluable in the solvent water “like dissolves like”
Explain why the density of ice is less than water
In liquid water the hydrogen bonds are constantly forming and breaking and molecules are densely packed. When water freezes, the hydrogen bonds hold the molecules in fixed positions. This generates a highly ordered structure In which the molecules are more widely spread therefore less dense
Giant covalent bond strength
Have many strong covalent bonds between atoms in a 3D structure which require a lot of energy to break which results in high mpts and bpts and they tend to be very hard. eg diamond and silica
Giant ionic bond strength
Strong ionic bonds in 3D structures which require a lot of energy to break resulting in very high mpts
Giant metallic bond strength
Strength incraeses as:
-The charge on the positive ion increases
-The size of the positive ion decreases
-The number of delocalised e- per atom increases
Non polar atoms and noble gas atom bond strength
Only have weak vdw foa between molecules (atoms for noble gases) which are easy to break and therefore have low mpts and bpts. Therefore they tend to be gases, liquids or low mpt solids. As molecules and atoms become larger and therfore have more e-, vdw become sronger and mpts and bpts increase
Polar molecules bond strength
Have both vdw and dipole dipole attractions therefore have higher mpt and bpt than non-polar molecules because of the stronger I.M forces
Molecules which exhibit hydrogen bonds strength
Also have dipole dipole and vdw as hydrogen bonds are very strong and require a lot of energy to break
Bond types in order of strongest to least strong
Hydrogen bonds>dipole dipole>vdw
Trends in mpt and bpt down groups pt1
HF xhibits the strongest I.M force, hydrogen bonding between neighbouring mlecules :. requires the most energy to break :. has the highest bpt for the group 7 hydrides
Trends in mpt and bpt down groups pt2
After HF there is a drop in bpt and then a gradual increase again. In HCl there are no hydrogen bonds but it is polar. Only 20% of I.M. forces are dipole-dipole, the other 80% is instantaneous induced dipole-dipole/ Van der waals. om HCl to HI there is a decrease in strength in dipole-dipole forces, yet bpt goes up? This is because instantaneous dipole induced dipole have moe signficant effect
Viscosity explained
(WHY DOES X HAVE A GREATER VISCOSITY THAN Y)
Explain bonds, then “the molecules of X cannot slide over each other as easily”
