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MEHC U2 > Intermolecular forces and polarity > Flashcards

Intermolecular forces and polarity Flashcards

1
Q

What are the 5 different types of molecular shapes?

A 
Linear
V-shaped
Triangular pyramidal 
Triangular planar
Tetrahedral
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2
Q

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

A

1 or 2 atoms

No lone pairs

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3
Q

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

A

3 atoms

Has Lone pairs

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4
Q

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

A

4 atoms

Has Lone pairs

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5
Q

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

A

4 atoms

No lone pairs

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6
Q

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

A

5 atoms

No lone pairs

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7
Q

Define Polar

A

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

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8
Q

Define non-polar

A

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

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9
Q

What is the bond angle for a linear shape?

A

180º

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10
Q

What is the bond angle for a triangular planar?

A

120º

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11
Q

What is the bond angle for a tetrahedral shape?

A

109.5º

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12
Q

What is the bond angle for a pyramidal shape?

A

less than 109.5º

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13
Q

What is the bond angle for a V shape?

A

several degrees less than 109.5º

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14
Q

What is dipole-dipole attraction?

A

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

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15
Q

What are dispersion forces (Van der Waals forces)?

A

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

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16
Q

What influences the strength of dispersion forces?

A

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.

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17
Q

What are hydrogen bonds?

A

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.

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18
Q

What is the relative strength of intermolecular forces?

>

A

Hydrogen bonding > dipole-dipole attraction > dispersion forces

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19
Q

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.

A

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.

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20
Q

Dispersion forces:

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

A

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.

21
Q

What are dispersion forces due to?

A

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

22
Q

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

A

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

23
Q

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

A

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.

24
Q

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

A

combinations of electrostatic attractions and repulsions

25
Q

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

A

cannot have dipole-dipole or hydrogen bonds

26
Q

How does electronegativity affect intermolecular forces?

A

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.

27
Q

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

A

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

28
Q

What intermolecular force do all molecules have?

A

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

29
Q

What intermolecular force do all polar molecules have?

A

Dipole-dipole forces

30
Q

What are the 5 Gas Laws?

A 
Boyle's Law
Charles' Law
Combined Gas Law
Avogardo's Hypothesis 
The Universal Gas Law or Ideal Gas Equation
31
Q

State Boyle’s Law

A

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

32
Q

How is Boyle’s Law mathematically written?

A

P1V1=P2V2

33
Q

State Charles’ Law

A

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

34
Q

How is Charles’ Law mathematically written?

A

V1/T1 = V2/T2

35
Q

State Combined Gas Law

A

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

36
Q

How is Combined Gas Law mathematically written?

A

P1V1/T1 = P2V2/T2

37
Q

State Avogadro’s Hypothesis

A

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

38
Q

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

A

Standard T= 0C or 273.15K
Standard P= 100kPA

at constant T&P Mole ratio=Volume ratio (all reactants and products must be gases)

39
Q

State the Universal Gas Law or Ideal Gas

A

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.

40
Q

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

A

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
41
Q

What is VSEPR theory for?

A

To decide the shape of molecules

41
Q

What is the VSEPR theory based on?

A

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

42
Q

How is VSEPR based on the Pauli exclusion principle?

A

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.

43
Q

Why is the water molecule V-Shaped?

A

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.

44
Q

Why is water polar?

A

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.

45
Q

What does 1g equivalent to in ml?

A

1g=1mL

46
Q

Converting Pa to atm

A

X101325

47
Q

Converting ATM to mmHg

A

760

MEHC U2 (8 decks)

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