57 terms

Material Science Chapter 2, Material Engineering Chapter 2


Terms in this set (...)

Bohr atomic model
In which electrons are assumed to revolve around the atomic nucleus in dis- crete orbitals, and the position of any particular electron is more or less well defined in terms of its orbital.
in terms of quantum numbers - n is the number of the orbital it is in (representing a fixed distance an electron has from the nucleus) and it shows that the electrons have specific energy levels where they need a certain amount of energy to go up a level or move down a level.
bonding energy
represents the energy that would be required to separate these two atoms to an infi- nite separation.
coulombic force
positive and negative ions, by virtue of their net electrical charge, attract one another.
electron configuration
represents the manner in which these states are occupied. ie 1s^22s^22p^1 for boron
atoms that readily accept electrons to form negatively charged ions, or sometimes they share electrons with other atoms.
elements, indicating that they are capable of giving up their few valence electrons to become positively charged ions.
electron state
values of energy that are permitted for electrons.
atoms of some elements have two or more different atomic masses.
hydrogen bond
a special type of secondary bonding, is found to exist between some molecules that have hydrogen as one of the constituents. strongest type of secondary bonding
ground state
When all the electrons occupy the lowest possible energies in accord with the foregoing restrictions.
Pauli exclusion principle
This principle stipulates that each electron state can hold no more than two electrons, which must have opposite spins. Thus, s, p, d, and f subshells may each accommodate, respec- tively, a total of 2, 6, 10, and 14 electrons
quantum mechanics
The establishment of a set of principles and laws that govern systems of atomic and subatomic entities.
quantum number
In wave mechanics, every electron in an atom is characterized by four parameters, n, l, m↓l,and m↓s.
van der Waals bond
weak in comparison to the primary or chemical ones, exists between virtually all atoms or molecules between electric dipoles, but its presence may be obscured if any of the three primary bonding types is present. Examples are polar bonds, induced polar bonds, and hydrogen bonds.
wave-mechanical model
The electron is considered to exhibit both wavelike and particlelike characteristics. An electron is no longer treated as a particle moving in a discrete orbital; rather, position is considered to be the probability of an electron's being at various locations around the nucleus.
- particles were shown to have a probable position, with the l value, describing a specific shape of the electron cloud
-ml and ms represent the wave-mechanical model of sub shells where each electron orbitals can have different orientations with electrons with different spins.
atomic number (Z)
For an electrically neutral or complete atom, the atomic num- ber also equals the number of electrons.
Principal quantum number : n
This quantum number is related to the distance of an electron from the nucleus, or its position and states the number of shells the atoms has. n= row of periodic table, n=1 is the first row, n=2 the second, n=3 the third and so on
Quantum number : l
Signifies the subshell, which is denoted by a low- ercase letter—an s, p, d, or f; it is related to the shape of the electron subshell. The number of these subshells is restricted by the magnitude of n.
Quantum number : ml
The number of energy states for each sub-shell. For an s subshell, there is a single energy state, whereas for p, d, and f subshells, three, five, and seven states exist. Two electrons can occupy each state. S can have 2, p can have 6, d can have 10 and f can hold 14 electrons.
Quantum number: ms
Associated with each electron is a spin moment, which must be oriented either up or down. For which two values are possible 1/2 and -1/ 2, one for each of the spin orientations.
Valence electron
Electrons that that occupy the outermost shell.
Electronegativity trend
As a general rule, electronegativity increases in moving from left to right and from bottom to top.
The percent ionic character (%IC) of a bond
It is possible to have interatomic bonds that are partially ionic and partially covalent, and, in fact, very few compounds exhibit pure ionic or covalent bonding.
Hybrid orbital sp
Linear with 2 regions.
Hybrid orbital sp²
Trigonal planar, 3 regions.
Hybrid orbital sp³
Tetrahedral 4 regions.
Hybrid orbital sp³d
Trigonal bipyramidal 5 regions.
Hybrid orbital sp³d²
Octahegral 6 regions.
Is the basic unit of matter.
Atomic Number
-number of protons in the nucleus of atoms
-number of electrons in neutral species
Higher the atomic number...
Higher the atomic weight
1 mole of matter equals=
6.022x10^23 molecules or atoms.
Quantum Numbers
Electrons in atoms are characterized by quantum numbers.
- so how electrons are characterized.
principal quantum no.(n = 1,2,3,4,.. or, K, L, M, N)
second quantum no.(s, p, d, and f)
- s
- s,p
- s,p,d
- s,p,d,f
Energy States
third quantum no.
Spin Moment
fourth quantum no.
Noble Gases
Helium(He), Neon(ne), Argon(Ar), Krypton(Kr)
-full outer valence electron shell
- very non-reactive
-inert gases
Valence Electrons
Are those that occupy the outermost filled shell.
-participate in the bonding between atoms to form atomic and molecular structures.
- many physical and chemical properties are based on the valence electrons.
Groups in the Periodic Table
vertical columns
Periods in the Periodic Table
Horizontal rows
-metallic shine or luster
-solids at room temp.
-malleable(shape without breaking) and ductile(stretch)(so we can shape them into whatever we want)
-Good conductors of heat and electricity
-rarely have metallic luster
-usually gases at room temp.
-neither malleable nor ductile
-poor conductors of heat and electricity
properties from both metals and non-metals
Ionic Bonding
- occurs between + and - ions
- requires electron transfer
- large difference in electronegativities is required
- nondirectinal (surrounded by the same element on all sides
- example: naCl (na is surrounded by Cl on all 6 sides (3D))
-mainly in ceramics
Covalent Bonding
-Shared electrons
-directional, meaning magnitude of bond depends on direction. (properties of material vary ie strength or isulator vs semiconductors
-predominant bonding in Polymers.
-materials are less dense than metallic and ionicly bonded meterial because of its directionality, causes there to be more open space within the structures were as ionic and metallically bonded atoms are able to be closely packed with eachother.
-have polar molecule induced dipoles that cause vanderwaal bonding
Metallic Bonding
Arises from a sea of donated valence electrons
-primary bond for metals and their alloys
-nondirectional bond
-delocalized as electron cloud
-fluctuating induced dipoles from sea of electrons cause momntary vanderwaal bonds
Polar Molecules
Molecules with asymmetrical arrangement of postive and negative regions.
materials properties are the same in all directions.
- Ionic Bonds
- Metallic Bonds
Bond Length (variable)
Bond Energy (variable)
Melting Temperature (variable)
- Tm is larger if Eo is larger
coefficient of thermal expansion
same element but diff number of neutrons
first 10 elements
secondary bonds create
-surfacants - coupounds that lower the surface tension of a liquid ie soaps
-emulsifiers - added to liquid allows one particle to be suspended in the other
-desiccants- materials form hydrogen bonds wmixedith water and removes moisture
mixed bonds
a material is usually never one single primary bond, usually has two types