Intermolecular forces and polarity

Question 1

What are the 5 different types of molecular shapes?

Answer 1

Linear
V-shaped
Triangular pyramidal 
Triangular planar
Tetrahedral

Question 2

How many atoms in a molecule and lone pairs can a Linear shape have?

Answer 2

1 or 2 atoms

No lone pairs

Question 3

How many atoms in a molecule and lone pairs can a V-shape have?

Answer 3

3 atoms

Has Lone pairs

Question 4

How many atoms in a molecule and lone pairs can a Triangular pyramidal have?

Answer 4

4 atoms

Has Lone pairs

Question 5

How many atoms in a molecule and lone pairs can a Triangular planar have?

Answer 5

4 atoms

No lone pairs

Question 6

How many atoms in a molecule and lone pairs can a tetrahedral have?

Answer 6

5 atoms

No lone pairs

Question 7

Define Polar

Answer 7

uneven charge distribution between a bond due to the arrangement of electrons

Question 8

Define non-polar

Answer 8

electrons are equally shared so there is an even charge distribution across a molecule

Question 9

What is the bond angle for a linear shape?

Answer 9

180º

Question 10

What is the bond angle for a triangular planar?

Answer 10

120º

Question 11

What is the bond angle for a tetrahedral shape?

Answer 11

109.5º

Question 12

What is the bond angle for a pyramidal shape?

Answer 12

less than 109.5º

Question 13

What is the bond angle for a V shape?

Answer 13

several degrees less than 109.5º

Question 14

What is dipole-dipole attraction?

Answer 14

attractions occur between the partially positive end of one molecule and the partially negative end of a different molecule.

Question 15

What are dispersion forces (Van der Waals forces)?

Answer 15

Act between all molecules and are the only type of intermolecular force that acts between non-polar molecules.

Dispersion forces are the weakest of all
the types of intermolecular forces because they act between temporary dipoles

Question 16

What influences the strength of dispersion forces?

Answer 16

influenced by the total number of electrons in the molecule.

The higher the number of electrons, the stronger the dispersion forces acting between the molecules.

Question 17

What are hydrogen bonds?

Answer 17

A hydrogen bond is the attraction of the partially positive hydrogen atom (from an H-F, H-O or H-N bond) for a non-bonding electron pair on a F, O or N atom of a neighbouring molecule.

Hydrogen bonds are the strongest intermolecular force as they exist between very polar molecules.

Question 18

What is the relative strength of intermolecular forces?

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Answer 18

Hydrogen bonding > dipole-dipole attraction > dispersion forces

Question 19

Dispersion forces:
State which example from butane (C4H10) BP= -0.5C and its isomer methylpropane (CH3CH(CH3)2) BP= -11.7C, has the higher dispersion forces.

Answer 19

Butane has greater dispersion forces due to its higher BP and linear shape.

Though both substances have the same number of electrons per molecule. However dispersion forces are greater for linear molecules rather than spherical molecules. This is due to the higher S.A of the linear shape.

Question 20

Dispersion forces:

State which example from chlorine (Cl2) BP= -35C and nitrogen (N2) BP= -196C, has the higher dispersion forces.

Answer 20

Cl2 has higher BP than N2, therefore it has stronger dispersion forces.

As the greater number of electrons per molecule increases, dispersion forces increases in strength.

Question 21

What are dispersion forces due to?

Answer 21

Due to the random motion of electrons, then the strength of this force increases as the number of electrons in the molecule increases.

Question 22

What do the different melting points of Galactose (167C) and Glucose (146C) indicate about the relative strength of the intermolecular forces between the two?

Answer 22

When a molecular substance melts, the intermolecular forces have been partly overcome.

High melting points indicate molecules need a high kinetic energy in order to particularly overcome their mutual attraction (intermolecular forces) and change from the solid to the liquid phase.

This glucose has weaker intermolecular forces (lower BP) than galactose which as a stronger intermolecular force, due to its high BP

Question 23

Explain the formation of dipole-dipole forces in molecular compounds using hydrogen sulfide as an example H2S.

Answer 23

It is polar, thus had an uneven distribution of charge. H has a slight (s+) charge, while S has a slight (s-) charge.

Adjacent molecules in a sample of H2S will attract (weakly) by aligning opposite charges of their dipoles.

Question 24

What causes the alignment of molecules for dipole-dipole attraction?

Answer 24

combinations of electrostatic attractions and repulsions

Question 25

What type of intermolecular forces can't non-polar molecules have?

Answer 25

cannot have dipole-dipole or hydrogen bonds

Question 26

How does electronegativity affect intermolecular forces?

Answer 26

Two atoms of different electronegativity form a covalent bond. Uneven sharing of the bonding electrons will occur. It happens as the shared electrons of the bond spend more time closer to the more highly electronegative element.

Question 27

What happens when there is a greater difference in electronegativity of the two covalently bonded atoms?

Answer 27

The greater the difference in electronegativity of two covalently bonded atoms, the greater the size of the bond dipole

Question 28

What intermolecular force do all molecules have?

Answer 28

Dispersion forces has the rapidly fluctuating electrons orbiting the molecule. The force is due to the rapid movement of electrons in the cloud of electron density surrounding the molecule

Question 29

What intermolecular force do all polar molecules have?

Answer 29

Dipole-dipole forces

Question 30

What are the 5 Gas Laws?

Answer 30

``` Boyle's Law Charles' Law Combined Gas Law Avogardo's Hypothesis The Universal Gas Law or Ideal Gas Equation ```

Question 31

State Boyle's Law

Answer 31

States that at a constant temperature, the pressure of a gas is inversely proportional to the volume of the gas Smaller volume, Increased pressure Larger volume, decrease pressure

Question 32

How is Boyle's Law mathematically written?

Answer 32

P1V1=P2V2

Question 33

State Charles' Law

Answer 33

States that at a constant pressure, the volume of a fixed quantity of a gas is proportional to its absolute (kelvin) temperature.

Question 34

How is Charles' Law mathematically written?

Answer 34

V1/T1 = V2/T2

Question 35

State Combined Gas Law

Answer 35

Describes how gases behave when pressure, temperature and volume are all changing. It is a combination of Boyle's and Charles' Law

Question 36

How is Combined Gas Law mathematically written?

Answer 36

P1V1/T1 = P2V2/T2

Question 37

State Avogadro's Hypothesis

Answer 37

states that equal volumes of different gases, measured at the same temperature and pressure, contain the same number of particles

Question 38

What is the Standard pressure and temperature for molar volume of any gas measured at?

Answer 38

Standard T= 0C or 273.15K Standard P= 100kPA at constant T&P Mole ratio=Volume ratio (all reactants and products must be gases)

Question 39

State the Universal Gas Law or Ideal Gas

Answer 39

combines Boyle's Law, Charles' Law and Avogadro's Hypothesis and gives the relationship between pressure, temperature, volume and number of moles of a gas.

Question 40

How is Universal Gas Law/Ideal Gas equation mathematically written?

Answer 40

PV = nRT ``` where P= Pressure in kPA V= Volume in L n= no of moles of gas R= 8.314 J K-1 mol-1 T= Temp in K ```

Question 41

What is VSEPR theory for?

Answer 41

To decide the shape of molecules

Question 41

What is the VSEPR theory based on?

Answer 41

On the principle that electrons pairs want to be as far away from each other as possible

Question 42

How is VSEPR based on the Pauli exclusion principle?

Answer 42

based on the Pauli exclusion principle that concludes that two electrons with the same spin have zero probability of being found in the same location and will in fact be found in locations that are as far apart as possible.

Question 43

Why is the water molecule V-Shaped?

Answer 43

The water molecule is V-shaped due the increased repulsion of the non-bonding electron pairs. Oxygen atoms are much more electronegative than hydrogen atoms and therefore the bonding electrons spend more of their time closer to the oxygen nucleus than the hydrogen nucleus.

Question 44

Why is water polar?

Answer 44

Due to the V-shape and polar bonds holding the molecule together there is an uneven electron distribution within a water molecule. The water molecule is said to be polar because one end of the molecule is less electron dense than the other.

Question 45

What does 1g equivalent to in ml?

Answer 45

1g=1mL

Question 46

Converting Pa to atm

Answer 46

X101325

Question 47

Converting ATM to mmHg

Answer 47

760