2. Forces and Potentials Flashcards
What is a covalent bond?
A chemical bond between molecules that originates from the sharing of valence electrons to facilitate the filling of electron shells within atoms, forming stable structures.
Why are covalent bonds directional?
There is mutual repulsion of the electrons in different bond orbitals, which causes the bond to form.
Covalent forces (bonds) operate over ____ distances.
Short
What distances do covalent forces operate over?
0.1-0.2 nm
What is the energy associated with the formation of a covalent bond?
2-8 eV per bond
What is a metallic bond?
Bonding between metal atoms in which electrons become delocalised throughout the material so that they are shared between many nuclei.
Which 2 features of a metal result from metallic bonding?
- Shine
- Conductivity
What are Coulomb interactions?
The electrostatic force between two interacting atoms that each have a net charge.
Give the equation for the potential energy of two molecules with charge, separated by a distance
U(x) = potential energy
q = charge
ε = permittivity
x = separation distance
Many different types of potential have an _______ _____ ___ dependence.
Inverse power law
The ______ the value of n in a power law dependence, the shorter the range of interaction
Greater
When a potential energy is _______, the interaction is favourable (attraction).
Negative
U < 0
When a potential energy is ______, the interaction is unfavourable (repulsion).
Positive
U > 0
Give the equation for the range of an electrostatic interaction
X = range
q = charge
ε = permittivity
k = Boltzmann’s constant
T = temperature
At what distance is an electrostatic interaction significant?
when the separation distance is smaller than the range of the interaction: x < X.
What type of interaction is responsible for forming ionic crystals?
Electrostatic interactions
State the equation used to calculate the (cohesive) energy per ion pair holding a crystal together
U = cohesive energy
e = electron charge
α = Madelung constant
ε = permittivity
r = separation distance
What is the Boltzmann probability?
The probability that two objects which are held together by an attractive interaction will escape due to thermal fluctuations.
Give the equation for the Boltzmann probability
P(x) = probability
k = Boltzmann’s constant
T = temperature
Give the equation that relates the force on an object to its potential energy
F = force
U = potential energy
x = distance
_______ forces are attractive.
Negative
_______ forces are repulsive.
Positive
Give the equation for the force acting between two point changes, separated by a distance
F = force
U = potential energy
x = separation distance
q = charge
ε = permittivity
The sign of an electrostatic force depends on the sign of the ______.
Charges
