Lecture 1 Flashcards
What are the two main types of materials?
1) Metal
- Ferrous
- Non-ferrous
2) Non-metal
- Polymers
- Ceramics
All fall under the category of Composite Materials
What are the types of material properties?
Mechanical Properties:
- Strength (compressive, tensile, strength)
- Stiffness - elasticity
- Toughness
- Hardness
- Plasticity - ductility, malleability
- Brittleness
Physical Properties:
- Density
- Melting/Boiling point
- Glass transition temperature
- Thermal conductivity, heat capacity, expansion, stability
- Electrical conductivity, permittivity
- Magnetic properties
- Optical transparency, refractive index, color
What are the different size scales?
Microscale: 10^-3 to 10^-7
Nanoscale: 10^-7 to 10^-9
Angstrom: 10^-10
Fall under the macroscale
What is the simple view of the atomic structure?
- An atom is a nucleus with electrons revolving around it
- Electrons are attached to the nucleus, which is why energy is required to remove them from the atom
- Electrons occupy different orbits, some closer and some further to the nucleus
- The further ones are more weakly attracted to the nucleus
- Number of protons (atomic number) = number of electrons
What is an Angstrom?
An Angstrom (Å) is a unit that equals to 1*10^-10 meters.
What is Electrostatic Interaction?
Electrostatic attraction:
- Between electrons and protons
Electrostatic repulsion:
- Between electrons and electrons
- Between one nucleus and another
Coulomb’s law
Electron attraction to the nucleus is strong, and electrons like to occupy the orbitals closest to the nucleus.
What are Atomic Orbitals?
Electrons occupy fixed orbitals which can hold a certain number of electrons.
1st shell: 2 electrons
2nd shell: 8 electrons
3rd shell: 18 electrons
4th shell: 32 electrons
What are Orbital Energy Levels?
The closer the shell to the nucleus, the lower energy it is.
Electrons like to occupy the lowest energy shells available as they are closest to the nucleus.
We require a lot of work to remove electrons close to the nucleus due to their high level of attraction.
What are s, p, d and f in Orbital Energy Levels?
The shells are split into the orbitals s, d, p and d. Each orbital can only hold 2 electrons, however the number of orbitals there is differs according to the letter.
The first shell is made up of one s orbital, as it can only hold 2 electrons.
The second shell is made up of one s orbital and three p orbitals, since it can hold up to 8 electrons.
The third shell is made up of one s orbital, three p orbitals and five d orbitals, since it can hold up to 18 electrons.
The fourth shell is made up of one s orbital, three p orbitals, five d orbitals and seven f orbitals, since it can hold up to 32 electrons.
How does the periodic table relate to this?
The periodic table tells us things like the atomic number (no. of protons and electrons) and the mass.
Groups = columns
Periods = rows
All the elements in one group have the same outer outer orbital configuration. For example, Hydrogen has 1 electron in its outer orbital meaning Lithium, Sodium and the rest of the elements in Hydrogen’s group would have 1 electron in their outer orbital as well.
What is Shorthand Notation?
A shorter way to describe the configuration of the electrons in an atom.
For example, Neon would be:
1s^2 2s^2 2p^6
What are the three factors that determine the reactivity of each element?
1) As the atomic number (no. of protons) increases, the pull on the electrons increases making them harder to pull away from the atom.
2) Electrons further from the nucleus are easier to remove than the inner ones
3) Electrons further from the nucleus can be screened from the attraction of the nucleus by electrons in inner orbitals, making them easier to remove.
What are the Approximate Energy Levels of Atomic Orbitals?
The energy levels are dependent on the positive charge (protons) in the nucleus.
For example, in the case of Hydrogen, since there is only one proton in the nucleus there is not much attraction with the electron, making it easy to remove.
For Helium, there is a stronger attraction due to the increased positive charge, meaning more energy is needed to remove an electron.
For Lithium, the electrons in the inner shell are very strongly attracted to the nucleus, meaning a lot of energy is required to remove an electron. As for the electron in the second shell, it is weakly attracted due to electron repulsion as well as the inner electrons are screening it, making it easy to remove.
For Neon, the electrons in the inner shell are extremely attracted to the nucleus due to the high positive charge. The electrons in the second shell are also strongly attracted to the nucleus despite the screening and electron repulsion because of the high positive charge in the nucleus, meaning it is difficult to remove an electron and a lot of energy is required. The electrons in the s orbital are more strongly attracted than those in the three p orbitals.
What is Ionisation Energy?
It is the energy required to remove the least stable electron from an atom. A high ionisation energy indicates that it is difficult to remove an electron.
The ionisation energy is lower if there is an electron on its own in the outer shell, and higher if it is not.
When shown in a graph, there are lots of fluctuations going up and down showing that the maxima is at the noble gases, and minima at the alkali metals (Noble gases have full outer shells and alkali metals always have an electron on its own).
