Quiz 1 Flashcards
What does the bohr modle describe
It describes “relatively” well the arrangement of subatomic particles and the position and energy of the particles.
Principal Quantum Number “n”
Always an integer. Specifies a particular position of electrons -> SIZE FACTOR.
n= 1(K) 2(L) 3(M) 4 (N)…
Azimuthal Number
“l” governed by the value if “n”
- l = 0… (n-1)
-l = 1(s) 2(p) 3(d) 4(f)…
Magnetic Number
“m_l”
- number of electrib orbitals in each subshell.
-for neutral atoms, orbitals are symmetrical but under the influence of electricity or magnetism, the orbitals can change shape.
Spin
“m_s”
- The electrons have a rotation cw or ccw which creates a moment up or down. To fully describe an atom we need to know the magnitude/value of the quantum numbers.
-> This is essential for bounding of elements
Valence
Electrons in outermost shell.
Full valence= inert or non reactive
Coordination Number
How many neighboring atoms a reference atom has. A max CN is 12 due to the 3D arrangement of atoms. Possible when R = r= 1
Ionic bonding
Results from electron transfer from one element to another.
The bind force between the anion and cations is the equilibrium between:
- Attraction b/w nucleus and valence e cloud
- Repulsion between nucleus and nucleus
The greater the bond force, the higher the melting point.
Covalent Bonding
Results from sharing electrons between two adjacent atoms. The geometry of the molecule also becomes important and may be more relevant than bonding force. Ie linear vs shape
Metallic Bonding
In metals the valence electrons are able to move in any direction they create an electron cloud which is mobile. The purer the metal is the easier it is to move electrons
Secondary (Van der Waals) Force Bond
E’s are not necessarily shared between atoms. By bringing atoms together, the distribution of e’s is affected. We form a “dipole” generated by the asymmetry of the electron cloud.
The molecules dipoles can then attract/ repel other molecules.
Unit Cell
The fundamental crystalline structure in a material that is repeated in 3D throughout the material.
The lattice parameter
The size and shape of the unit cell
Seven different unique cell shapes
-Cubic
-Tetragonal
-Orthorhombic
-Rhombohedral
-Hexagonal
-Monoclinic
-Triclinic
Body centered cubic
In this cell atoms are in the corners and one atom is in the middle. The size of three cell depends on the radius R of the atom: a= 4R/sqrt(3). A total of 2 atoms per BCC unit cell. It is considered relatively open and may not be stable.
Face centered cubic
FCC. In this cell the atoms are at the edges of the cube and in the faces of the cube. Assuming that the atoms are touching a= 2Rsqrt(R). A total of 4 atoms are in a fcc unit cell.
Hexagonal Close packed
HCP. A common non cubic lattice. It has two lattice parameters a and c. It includes 6 total atoms
The theoretical density if a material
p = nA/(Vc Na)
n- number of atoms in a cell
A- atomic weight
Vc- volume of unit cell
Na- avogadros number 6.022*10^23 atoms/mol
Directions in a crystal
Is defined as a multiple of the coordinate axes. Since we use a unit cell then the magnitude if the vector is scales to be 1
u = n(x2-x1)/a
v= n(y2-y1)/b
w= n(z2-z1)/c
Directions labeled [u v w]. If a value is negative put a bar above the number!
Metal Properties
Dense, stiff, strong, ductile
Good conductors of electricity and heat
Ceramic Properties
Combo of metals and nonmetals
Oxides, carbides, Nitrides, Borides
Very hard, strong, abrasion resistant, brittle
Poor thermal conductors
Polymers (plastics) properties
Natural rubber
Hydro carbons with various additives
Low density and good specific properties
Degradation under UV
Composites
Combos of metals ceramics and polymers
Designed to target certain properties
Shrodingers model
Probable electron distribution but cant tell till you look. Cat in box
