Materials

What is atomic number?

The number of protons (or in a neutrally charged atom, also the number of electrons) in the nucleus of an atom, which determines the chemical properties of the element.

What is atomic mass?

The sum of protons and neutrons in the nucleus of an atom.

What is an isotope?

A variant of an element that has the same number of protons but a different number of neutrons

What is atomic weight?

The average of the atomic masses of naturally occuring isotopes

What is the atomic mass unit

1/12 the mass of C12, 1 amu = 1.7 × 10^-24 g

What is the conversion between atomic mass and molar mass?

amu/atom = g/mol

What is a quantum number?

it is used to define the position of any electron within it’s orbital

What are the quantum mechanical principles?

electrons may only have specific values of energy. electron energies are associated with energy levels or states. These energies can chenge through absorption or emission.

What are the principle quantum numbers

(n) energy level shell, demonstrating how close it is to the nucleus with designation 1, 2, 3 ect.

What are the azimuthal quantum numbers

(l) subshell, demonstrating shape of the orbital with designation spdf

What are the magnetic quantum numbers

(mI) defines no. of energy states in l, and how many orbitals with that shape exist with designation 1, 3, 5, 7 (-l to +l)

What are the spin quantum numbers

(ms) defines orientation of the electron with designation +1/2, -1/2 2 per state.

What are valence electrons

the electrons that occupy the outermost shell

What do valence electrons do

the electrons are the most available for bonding and control the chemical properties of the material

What are periods in the periodic table

the rows

what are groups in the periodic table

the columns

Where are the alkali metals on the table?

Group IA

Where are the alkali earth metals on the table?

Group IIA

Where are the noble gases on the table?

Group O

Where are the Halogens on the table?

Group VIIA

Where are the transition metals on the table?

Groups IIIB to IIB, with partically filled d electron states

What is electronegativity?

An atom’s ability to attract shared electrons in a bond

Where on the periodic table does electronegativity increase?

Starting in the bottom left with francium at 0.7, moving up to the top right to fluorine at 4

What are the primary bonds?

Ionic, Covalent and Metallic

What are the secondary bonds?

Van der Waals and Hydrogen

How does ionic bonding occur?

transfer of an electron between a cation and anion which have very dissimilar electronegativities such as with a metal and nonmetal

What are the properties of ionic bonds?

They are non-directional. Have high bonding energies (around 600-1500 kJ/mol). Have high melting temperatures. are hard and brittle. are insulative. the predominant bonding type in ceramic materials.

How does covalent bonding occur?

sharing of electrons in valence shell between atoms of comparable electronegativities typically non-metals.

What are the properties of covalent bonding?

They are generally directional. Have varying but strong bonding energies (around 150-1000 kJ/mol). Have low melting and boiling temperatures. are soft and brittle. with the exception of network covalent bonds which have high MP and are very hard. are insulative. the predominant bonding type in silicate ceramic materials.

How to find the number of covalent bonds for a particular compound?

8-N’ (N’ is the number of valence electrons)

How to find percentage ionic character?

% = {1 - exp[-(0.25)(Xa-Xb)²]}*100

How does metallic bonding occur?

sharing of valence electrons in cloud around ion cores with a net positive charge. found in metals and their alloys

What are the properties of metallic bonds?

Have varying bonding energies, may be weak or strong (around 60-900 kJ/mol). Have high melting and boiling temperatures. Are strong tough and malleable. Have high densities, are ductile, opaque, shiny and lustrous.. are good conductors.

How does Van der Waals occur?

attraction between the fluctuating dipoles of the asymmetric electron clouds of atoms

How does Hydrogen bonding occur?

Occurs between H-F, H-O and H-N.

What are the properties of Hydrogen bonding?

Strongest of the secondary bonds. relatively high melting and boiling points when considering the low moledular weights.

What is the term for an orderly array of atoms with a repeating unit?

Crystalline

What is the term for non-crystalline materials?

Amorphous

Properties of crystalline materials?

Periodic stacking. Typically metals and ceramics

Properties of amorphous materials

Atoms have no predictable location. there are no repeating units or structure. Glass is an example.

What is a crystal lattice?

3D array of points coinciding with atom positions

What is a unit cell?

Smallest repetitive entity in a crystal. basic structural building block

what are the lattice parameters?

a, b, c, alpha, beta, gamma, describe the size and shape of the unit cell.

What are the reasons for dense packing in metals?

Material is composed of a single element so all atomic radii are identical. Metallic bonding is not directional. distances between unit cells tend to be small therefore lower bond energy is needed. Electron cloud of metallic bonding shields the ion cores from each other.

Properties of a simple cube crystal system

Coordination no. 6, rare due to low packing density (only Po)

What is the coordination number?

the number of nearest neighbors or touching atoms in a unit cell

Properties of a body centered cube crystal system

coordination no. 8. cubic arrangent with an aditional atom in the centre. examples include iron, cr, w

Properties of a face centered cube crystal system

coordination no. 12 cubic arrangement with an atom along each face examples include Al, Cu, Au, Pb

Properties of a hexagonal close packed crystal system

Coordination no. 12, Top and bottom faces have six atoms surrounding a single centre atom, between the faces are three central atoms. examples include magnesium, zinc, ti

What are isotropic materials

Have the same properties in all directions

What are anisotropic materials

The properties are direction dependant

How to find the crystallographic direction

First, reposition vector if necassary such that it passes through origin. Next, identify the top of the vector in terms of unit cell a, b, c. Adjust to smallest integer values if required. To record result, encolse the three indexes in square brackets, no commas with a bar atop for negative values.

What is a family of directions

<xyz> where systems with the same direction but different notations are summarised (eg cubic [100], [010], [001])

How to find the crystallographic Planes?

First, reposition origin or add a parallel plane such that the plane does not pass through origin. Next, identify the intercepts between the plane and each axis, if parallel it is infinite. take reciprocals of the intercepts (inf→0). reduce to smallest integer values. To record result, encolse the three indexes in round brackets no commas.

Miller indices properties

Parallel planes are equivalent

Negative planes are equivalent (abc) = -(abc)

notation of individual planes = (abc)

notation for families of planes = {abc}

What does it mean for a material to be polycrystalline?

It is composed of many small single crystals called grains

When does a grain boundary occur?

When crystals of different orientations intersect

What do imperfections in crystals impact?

They control the plasticity in metals, conductivity and diffusivity

What is a point defect

a 0D imperfection in a crystal

What are the types of point defects?

Vacancy, where a unit cell is missing. Self-interstitual (rare in metals) where a unit cell is inserted between cells in the array.

What is a line defect?

a 1D impefection in a crystal

What is a plane defect?

a 2D imperfection in a crystal

What is a solid solution

the addition of impurity atoms to a metal

What is a solvent

the element or compound that dominates the solution

What is a solute

The minority element or compound in a solution

How does a solid solution occur?

When solute atoms replace the solvent atoms in random locations

What types of solid solutions are there?

Substitutional, replacing the solvent atom entirely. Interstitial where a smaller atom slots itself into a gap in the array

Types of line defects

Edge dislocation results in an extra half-plane of atoms inserted in a crystal structure, b is perpendicular to dislocation line. Screw dislocation results in a spiral planar ramp because of a shear deformation, b is parallel to dislocation line.

Types of Plane defects

grain boundaries, referring to the regions between crystals where the transition between each crystal is slightly disordered due to different orientations.

What are the properties of atoms and low density in grain boundaries

high mobility, high diffusivity, high chemical reactivity

What is Strength?

The measure of how much load a material can resist

What is Ductility?

The measure of how much a material can stretch prior to failure

What is toughness?

The measure of a material's ability to absorb energy and withstand impact

What properties contribute to toughness?

Strength and ductility

What is hardness?

A Material's resistance to plastic deformation by an indent or scratch

To add

Compare the types of stresses with their images

What is the equation for stress?

Stress= force/initial area =MPa=N/mm^2

What is the equation for strain?

Strain=change in length/initial length

What is plastic deformation?

Deformation of a material that cannot be recovered

What is elastic deformation?

Deformation of a material that can be recovered and hence is reversible

Where does plastic deformation sit on the stress and strain plot?

It is the region where the trend is no longer linear

Where does elastic deformation sit on the stress and strain plot?

It is the initial linear region of the plot

What is the equation for Hooke's Law?

FILL LATER

What is the equation for Poisson's ratio?

FILL LATER

What is the equation for Yield Strength?

FILL LATER

What does Ultimate tensile strength refer to on the stress and strain plot?

The local maximum

What occurs before the UTS point?

The sample will deform unifromly along it's length

What occurs after the UTS point?

The sample will either fracture or begin to neck

What happens to the stress of a sample when it begins to neck?

It will reduce

What is the equation for ductility?

FILL LATER

What are the graphical points of interest on a stress vs strain plot?

UTS is the local maximum
Yield stress is the point where elastic deformation becomes plastic
Young's modulus is the linear slope of elastic deformation and ductility is the end of the plot referring to the elongation at fracture

What are the types of toughness measurements?

Impact toughness measured by breaking the sample under a fast moving pendulum and fracture toughness measured by the crack propagation rate

What may happen to a material's toughness as temperature increases?

They may transition from a brittle material to a ductile material

What is ductile fracture?

A fracture that occurs with significant plastic deformation

What is Brittle fracture?

A fracture that occurs with little or no plastic deformation

Why is a ductile fracture preferred to a brittle one?

There is little to no warning that the material is about to fail

What are the properties of a brittle fracture surface?

They tend to be shiny and sometimes show the grain texture. Often have facets or flat sections with no necking or plastic deformation

What are the properties of a brittle fracture surface?

They tend to be dull, at a microscopic level the fracture surfaces are very rough and will often show necking or plastic deformation next to the fracture site.

How will a plastic material react to a crack tip?

The crack will have a deformed region at the tip

How will a brittle material react to a crack tip?

The crack will have a sharp tip, propogating easier than a blunt tip