Matter is divided into?
Mixture and Pure Substance
Describe bonding in molecules:
Molecules have primary bonds within the molecule and secondary bonds between molecules
Define solid
“Solids” (for our purposes) have primary bonds between all atoms in the substance so that a crystal or 3D network
exists
Three primary bonds?
- Ionic
- Metallic
- Covalent
2 secondary bonds?
- Van der waals
- Hydrogen
Threshold electronegativity for ionic bonds? (Difference in electronegativity)
> 1.7
For electronegativity below 1.7, of the average electronegativity is high, what bond is it?
Covalent as outer shell is almost filled
For electronegativity below 1.7, of the average electronegativity is low, what bond is it?
Metallic and outer shell is nearly empty
What is ‘no directionality’ and which bonding is associated with it?
Radically symmetric. Thus can from a number of different crystall structures
Apart of ionic bonding
Metallic bonding properties:
- Zero or low electronegativity difference.
- Outer shell usually less than half full.
- The few electrons in the outer shell are not enough to fill the shells of two atoms if shared. They must be
shared between all the atoms in the material. - The electrons are delocalised
and freely move around all the
nuclei. - The result is high electrical
and thermal conductivity.
How do we get force from a well gragh?
Derivate of energy with respect to distance
The amount of energy to separate molecules or atoms is equivalent to?
The vertical distance from distance axis to tipping point
At what position is the energy at absolute zero (K=0)
Tipping point
Boling point trends as chain length decreases and why for alkanes:
Boiling temperature of alkanes (molecular liquids) decreases as chain length
decreases because van der Waals interactions decrease for smaller molecules
Yield Stress is?
The stress required to permanently (plastically) deform a material.
Elastic deformation is?
The material deforms under stress then springs back to its original shape when stress
is removed.
The coefficient of thermal expansion (CTE) is?
Materials usually expand as they are heated up
The maximum force to separate two atoms is equivalent to?
Yield strength
sigma = F * number of bonds per unit area
Elastic Modulus is?
a measure of how much deformation will occur for a given applied stress
(force). Atoms are pulled apart (or pushed together) slightly when a stress is applied.
Relation to hooke’s law and elastic modulus?
– Force between atoms is analogous
to the restoring force of a force spring atom spring in Hooke’s Law
- F=kD=kd
Modulus characteristics from gragh:
Sharp curvature = high modulus
Shallow curvature = low modulus
generally deeper wells (stronger bonding) will have sharper curvature.
