Attractions & Repulsions Flashcards
What 3 assumptions are made for the ideal gas equation?
- Molecules of the gas have zero volume
- There are no interactions between gas molecules
- All collisions are elastic (i.e have no energy loss)
What is the ideal gas equation, and what does each symbol represent?
pV = nRT
p = pressure (Pa)
V = volume (m^3)
n = no. moles
R = ideal gas constant (J K-1 mol-1)
T = temperature (K)
What determines the pressure of a gas?
- The frequency of molecules hitting the wall of the container
- The force the molecule exert on the wall when they hit (dependent on how fast they are moving)
Which combination of electronegativities tends to form covalent bonds?
Two highly electronegative atoms tend to form covalent bonds
Which combination of electronegativities tends to form covalent bonds?
Two highly electronegative atoms tend to form covalent bonds
Which combination of electronegativities tends to form ionic bonds?
One highly electronegative and one low electronegative atom tend to form ionic bonds
Which combination of electronegativities tends to form metallic bonds?
Two low electronegativity atoms tend to form metallic bonds
What are dipole moments?
Dipole moments are vectors that tell us the overall distribution of charge in the polar molecule
What are permanent dipoles?
Diatomic molecules containing two atoms with significantly differing electronegativities are said to have a permanent dipole (i.e. a permanent drawing of charge to one atom in the molecule)
Through what two methods can we measure if a molecule has a dipole moment?
- Microwave spectroscopy
- Measuring its dielectric constant
What is the difference in electronegativity for non-polar bonds?
Less than ~0.5
What is the difference in electronegativity for ionic bonds?
Greater than ~2
What is the difference in electronegativity for polar bonds?
Between ~0.5 and ~2
The greater the difference in electronegativity, the greater the…
Ionic character
What are two methods of measuring whether a molecule has a dipole moment?
Microwave spectroscopy
Measure it dielectric constant
How can we use microwave spectroscopy to find whether a molecule has a dipole moment?
In the gas phase, if the molecule has a dipole moment it will display a spectra
What is dielectric constant, and how does this tell us whether a molecule has a dipole moment?
Dielectric constant shows the ability of polar molecules to align in an electric field; if the molecule has a dipole moment, it will align
What is the equation for calculating the potential energy of dipole forces?
(Dipole moment 1 x Dipole moment 2) / Distance apart^3
Are there more intermolecular forces in liquids than solids?
No. There are more intermolecular forces in the solid state than liquid or gas
What is hydrogen bonding?
An extreme example of dipole-dipole interactions, between H and usually F, O or N
How many H-bonds form per water molecule?
4
Why do ionic compounds dissolve in water?
Water is able to break strong ionic bonds by forming ion-dipole bonds
What is polarisability of an atom?
The tendency of the electron field of an atom to become distorted when subjected to an electrical force
What is the relationship between polarisability and electronegativity?
There is an inverse relationship between polarisability and electronegative.
Highly electronegative elements are not easily polarised
What two factors increase polarisability?
- Larger molecular size
- More electrons
Name all the intermolecular forces in order of decreasing strength
STRONGEST
Ion-dipole
Dipole-dipole
H-bonding
Dipole-induced dipole
London forces
WEAKEST
What factors are responsible for dipole-induced dipole interactions?
The dipole moment of the polar molecule and the polarisability of the nonpolar molecule
What are London dispersion forces?
Induced dipole-induced dipole interactions
What feature of electron distribution allow London forces to form?
At any instant, the distribution of electrons are an atom will not be even, forming transient delta positive and delta negative dipoles
How do London forces form?
- Transient fluctuations in electron density
- Transient dipoles
- Transient induced dipoles in adjacent molecules
- Attraction between these dipoles are London forces
How does the size of the atom affect the strength of London forces?
The larger the atom, the more polarisable it becomes, so the stronger the London forces
How does the compactness of the molecule affect the strength of London forces?
The more compact the molecule, the weaker the London forces
What are the 4 types of crystalline solids?
- Molecular structures (e.g. CO2)
- Covalent network structures (e.g. Diamond)
- Metals (e.g. Fe)
- Ionic compounds (e.g. NaCl)
What is the electrical conductivity and melting/boiling point of molecular structures?
Electrical conductivity = low
Melting/boiling point = low
What is the solubility of molecular structures?
Some dissolve in water, many dissolve in organic solvents
What is the electrical conductivity and melting/boiling point of covalent network structures?
Electrical conductivity = generally low
Melting/boiling point = very high
What is the solubility of covalent network structures?
Generally insoluble in water and organic solvents
What is the electrical conductivity and melting/boiling point of metals?
Electrical conductivity = good
Melting/boiling point = generally high
What is the solubility of metals?
Insoluble
What is the electrical conductivity and melting/boiling point of ionic compounds?
Electrical conductivity = high when molten or in aqueous solution
Melting/boiling point = high
What is the solubility of ionic compounds?
Some soluble in water, but insoluble in organic solvents
Why does evaporation occur at lower temperatures, rather than boiling?
At lower temperatures, the vapour pressure of the liquid is lower than the atmospheric pressure, meaning bubbles cannot form
Why does boiling occur at higher temperatures?
At the boiling point, the vapour pressure of the liquid is equal to the atmospheric pressure, meaning bubbles can form and rise, and boiling occurs
What is equilibrium vapour pressure?
A measure of the tendency of molecules to escape from the liquid phase and enter the vapour phase (evaporate)
What is equilibrium vapour pressure dependent on?
- Temperature
- Intermolecular forces
What is the relationship between intermolecular forces and equilibrium pressure?
The weaker the intermolecular interactions, the higher the equilibrium vapour pressure
What is the conversion of solid directly to vapour known as?
Sublimation
What is the conversion of vapour directly to solid known as?
Deposition
What is the triple point?
The specific temperature and pressure on a phase diagram at which all three phases co-exist in equilibrium
What phases are present at pressures below the triple point?
At pressure below the triple point, we do not see liquids, just solids and gases
What is the critical point?
The point at which if you increase the temperature and/or pressure any further, you will get “supercritical fluid”
What is “supercritical fluid”?
The state at which the lines between liquid and gas become blurred; the density of the substance is close to that of a liquid, but the viscosity is like that of a gas
