polarities and intermolecular forces

Question 1

Octet rule exceptions

Answer 1

Beryllium is stable with 4 electrons, boron is stable with 6 electrons, phosphorous has 10 electrons in its shell in PCl 5, sulfur has 12 electrons in its shell in SF6

Question 2

Valence shell electron pair repulsion theory

Answer 2

way of predicting the shape of a molecule based on the number of bonding and lone pairs of electrons in polyatomic species

Question 3

What is valence shell electron pair repulsion theory based on

Answer 3

Based on the fact that the electron pairs interact and repel each other due to electrostatic repulsion meaning they adopt a spatial arrangement where the electron pairs are as fair apart as possible meaning electrostatic attraction is minimised

Question 4

What is polarity

Answer 4

Results form uneven partial charge distrubution

Question 5

What does polarity result from

Answer 5

Results from uneven partial charge distribution between various atoms in a molecule

Question 6

What atoms have partial negative charges

Answer 6

Atoms with more electronegativity

Question 7

What atoms have a partial positive charges

Answer 7

Atoms that are more neutral

Question 8

Electrons in a polar covalent bond

Answer 8

unequally shared between the 2 bonded atoms resulting in positive and negative charges

Question 9

Dipole

Answer 9

Separation of partial charges

Question 10

Polar bonds

Answer 10

covalent bonds which have a separation of charge, larger the difference in electronegativity between the 2 atoms the more polar the bond

Question 11

Non-polar covalent bonds

Answer 11

forms between 2 identical atoms when the electronegativities of the 2 atoms are equal and the electrons are shared equally (electronegativity difference is 0)

Question 12

Polar covalent bond

Answer 12

difference in electronegativities of the 2 atoms is greater than 0 but less than 2.0

Question 13

When is a bond ionic

Answer 13

If the difference in electronegativities is 2.0+

Question 14

What must occur for a molecule to be a polar

Answer 14

Contain one or more polar bonds, not be symmetrical

Question 15

3 types of intermolecular forces

Answer 15

Dispersion, dipole-dipole, hydrogen bonding

Question 16

Dispersion forces (4)

Answer 16

Exists between all molecules, Weakest intermolecular force, Only force of attraction between non-polar molecules, More significant as the molecules become larger

Question 17

What makes dispersion forces

Answer 17

Due to the creation of temporary dipoles when the molecules come close together, Dipoles form from uneven spread or dispersion of the constantly moving electrons, induced on one molecule by the other by forcing the electrons to the other side of the molecule, Dispersion forces result from the opposite charges attracting each other

Question 18

Dipoles

Answer 18

in polar molecules where the electron arrangement which causes one end of the molecules to be positively charged whilst the other end is negatively charged

Question 19

Dipole-Dipole interactions (forces)

Answer 19

Attraction between oppositely charged regions of different polar molecules, Stronger than dispersion forces, Significant intermolecular forces for small molecules

Question 20

Hydrogen bond

Answer 20

Extreme form of dipole-dipole attraction occurring in polar molecules, Strongest intermolecular force as the hydrogen is attracted to the most electronegative atoms (N,O,F)

Question 21

Strength of intermolecular forces

Answer 21

Hydrogen bonding > dipole-dipole > dispersion forces

Question 22

Comparing substances with the same intermolecular forces

Answer 22

Substance with the largest molecular mass/longest chain has higher melting/boiling point as it has a greater No of electrons

Question 23

Solubility

Answer 23

Measure of the ability for a solute to dissolve in a solvent at a given temperature, determined by knowing the type of binding that exists in both the solvent and solute, Depends on the strength of the attraction between the particles

Question 24

Solubility when substances have a similar type of bonding

Answer 24

solute will dissolve, polar solvents dissolve in a polar solute (like dissolves like)

Question 25

Solubility when substances have a different type of bonding

Answer 25

Won’t dissolve, non-polar solvents dissolve in non-polar solute

Question 26

Evaporation

Answer 26

when there is space above the liquid the particles at the surface have enough genetic kinetic energy to break the forces holding them and escape

Question 27

Vapour pressure

Answer 27

particles that escape a liquid in a closed container that collide with the walls of the container exerting pressure on the wall, tendency of molecules to escape the surface of a liquid

Question 28

When do particles collide with the liquid

Answer 28

If they have small enough kinetic energy meaning the particles can go back and forth between the liquid and the gas, As the amount of gas increases, it is more likely to bump the surface and get stuck meaning the rates of become gas and becoming liquid become the same establishing an equilibrium

Question 29

What does vapour pressure depend on

Answer 29

Intermolecular forces and temperature

Question 30

How do temperature and vapour pressure work together

Answer 30

if the temperature increases more molecules will have enough kinetic energy to escape the liquid and be gas meaning as the temperature increases the vapour pressure of a substance increases

Question 31

How do intermolecular forces and vapour pressure work together

Answer 31

if the molecule has strong intermolecular forces it will take more kinetic energy to escape the liquid meaning the vapour pressure is low, if the molecule has weak intermolecular forces they are easier to break meaning the particles in the liquid can escape easily meaning the vapour pressure will be high

Question 32

Volatile liquids

Answer 32

Have high vapour pressure as they evaporate quickly

Question 33

How does vapour pressure decrase/lower

Answer 33

addition of non-volatile solute which decreases the number of solvent molecules available on the surface of a liquid, greater the concentration of solute particles in the solution = lower vp

Question 34

Vapour pressure at boiling point

Answer 34

Equal to the external pressure applied to the liquid (most cases- atmospheric pressure)

Question 35

Bubble formation when boiling

Answer 35

form when the vapour pressure is equal to the external pressure, bubbles rise to the surface where they burst releasing the gas formed throughout the liquid, vapour inside the bubble has enough pressure to prevent bubble from collapsing

Question 36

Colligative properties of solutions

Answer 36

When a solute is dissolved in a solvent the resulting solution has different chemical and physical properties from the pure solvent, Change that occurs dependent on the concentration of the solute particles rather than the type of solute

Question 37

Colligative properties

Answer 37

properties of a solution that differ from the pure solvent

Question 38

Freezing point

Answer 38

temperature at which the vapour pressure of the solid and liquid phases is the same

Question 39

How is freezing point lowered

Answer 39

addition of a solute as the vapour pressure of the solvent is lowered, Freezing point is depressed as the average kinetic energy decreases when a liquid starts to freeze turning into a crystalline solid by losing energy that needs to be cooled further so the solute particles fit into the crystal pattern

Question 40

Water

Answer 40

Covalent compound that consists of a highly electronegative central oxygen atom covalently bonded to 2 hydrogen atoms, has hydrogen bonding, bent shape due to asymmetrical polar bonds

Question 41

How is density calculated

Answer 41

Dividing the mass of a substance by its volume

Question 42

What is the density of water

Answer 42

Solid state is less dense than liquid state (ice floats on water) due to the changes in the hydrogen bonds between water molecules as when cooled, molecules slow down losing their kinetic energy allowing the hydrogen bonds to bring them closer together

Question 43

Surface tension of water

Answer 43

Forces acting on the surface of liquids, Measure of the resistance of a liquid to increase in its surface area, Due to the strong forces of attraction (due to the hydrogen bonds) between the water molecules at the surface , Molecules on the surface feel attractive forces on one side (drawn to the liquid), Molecules in the middle are attracted in all directions

Question 44

Water melting and boiling point

Answer 44

High compared to other covalent molecular compounds due to strong hydrogen bonding that has to be overcome for it to change state