I.M. FORCES OF ATTRACTION

Question 1

Polar molecule’s FOA

Answer 1

Van der Waal and dipole dipole

Question 2

Polar molecules containing N/O/F-H bonds

Answer 2

Van der Waals, Hydrogen bonds, dipole dipole

Question 3

Unsymmetrical molecules/ polar diatomic molecules (HBr)

Answer 3

Van der Waals, dipole dipole

Question 4

Non polar symetrical molecules/ diatomic molecules (Cl2)

Answer 4

Van der Waals

Question 5

Factors that determine the electronegativity value of an element

Answer 5

-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

Question 6

As the size of the atom increases…

Answer 6

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

Question 7

Going across a period electronegativity…

Answer 7

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

Question 8

Going down a group electronegativity…

Answer 8

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

Question 9

Covalent character

Answer 9

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

Question 10

Criteria for the molecule to be NON-POLAR

Answer 10

-No lone pairs
-All the terminal atoms are identical
(symmetrical molecules, all the dipoles cancel out therefore non-polar)

Question 11

POLAR molecules explanation

Answer 11

The dipoles do not cancel out (unsymmetrical) therefore the molecule is polar

Question 12

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

Answer 12

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”

Question 13

Explain why the density of ice is less than water

Answer 13

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

Question 14

Giant covalent bond strength

Answer 14

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

Question 15

Giant ionic bond strength

Answer 15

Strong ionic bonds in 3D structures which require a lot of energy to break resulting in very high mpts

Question 16

Giant metallic bond strength

Answer 16

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

Question 17

Non polar atoms and noble gas atom bond strength

Answer 17

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

Question 18

Polar molecules bond strength

Answer 18

Have both vdw and dipole dipole attractions therefore have higher mpt and bpt than non-polar molecules because of the stronger I.M forces

Question 19

Molecules which exhibit hydrogen bonds strength

Answer 19

Also have dipole dipole and vdw as hydrogen bonds are very strong and require a lot of energy to break

Question 20

Bond types in order of strongest to least strong

Answer 20

Hydrogen bonds>dipole dipole>vdw

Question 21

Trends in mpt and bpt down groups pt1

Answer 21

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

Question 22

Trends in mpt and bpt down groups pt2

Answer 22

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

Question 23

Viscosity explained

Answer 23

(WHY DOES X HAVE A GREATER VISCOSITY THAN Y)
Explain bonds, then “the molecules of X cannot slide over each other as easily”