MAE 3324 CH2 Flashcards
Why should you have a solid knowledge of interatomic bonding in solids?
In some instances, the type of bond allows us to explain the properties of a material.
The atomic number is the number of…
Protons in the nucleus.
Atoms are separated on the PT by?
Atomic number
For an electrically neutral atom, what is the relationship between the atomic number and the number of electrons?
They’re the same number.
Define “Atomic Mass.”
The sum of the masses of protons and neutrons within the nucleus.
In an isotope, the number of _____ may vary.
Neutrons
Define “Atomic weight.”
The weighted average of all the atomic masses of all the naturally occurring isotopes.
Define 1 amu.
1/12 of the atomic mass of the most common isotope of carbon which is carbon 12.
What is avagodros number?
The number of atoms in one mole of material. 6.022E23 atoms/mole
.
Is amu/atom any different than grams/mole?
No, they’re the same thing.
Define “Quantum mechanics.”
A set of principles and laws that govern systems of atomic and subatomic entities.
What is mean by the saying “Electrons are quantized?”
They can only hold a certain amount of energy.
During a quantum jump, when an electron absorbs energy, it transitions to a _____ energy state.
higher
During a quantum jump, when an electron emits energy, it transitions to a _____ energy state.
lower
In the wave mechanical model, an electron is considered to exhibit what two characteristics simultaneously?
The electron behaves as both a wave and a particle simultaneously.
In the wave mechanical model, the position of the electron is described by what?
A probability distribution or “electron cloud.”
Shells are specified by?
A principal quantum number n, which may take on integral values beginning with unity (one).
How many electrons can fit in the 1s shell?
2
How many electrons can fill the 2s shell?
2
How many electrons can fill the 2p shell?
6
How many electrons can fill the 3s shell?
2
How many electrons can fill the 3p shell?
6
How many electrons can fill the 3d shell?
10
The first quantum number is related to what physical aspect of the atom?
The electrons average distance from the nucleus.
What does the second quantum number designate?
The subshell.
Name the values for the quantum number L and their subshell designations.
0 = s 1 = p 2 = d 3 = f
Electron orbital shapes depend on what quantum number?
L
The s orbitals are in the shape of?
Spheres.
The third quantum number stipulates what?
The number of electron orbitals for each subshell.
Extra Notes: This value is also referred to as the magnetic number.
The third quantum number is also called what?
The magnetic number.
When L=0, m_L can only have a value of what? This corresponds to what subshell?
Zero. This corresponds to an S subshell with only one orbital.
If L =1, what values can m_L take on, and what orbitals are possible?
M_L could be -1, 0, or 1
Three p orbitals are possible (px, py, and pz).
How many orbitals do “d” and “f” subshells have respectively?
5 and 7
In the absence of an external magnetic field, all orbitals within each subshell are?
Identical in energy.
What is the fourth quantum number and what values can it take on?
The spin moment (abbreviated as ms).
Values can take:
ms = +1/2 = spin up
or
ms = -1/2 = spin down
T or F
The smaller the principal quantum number the lower the energy?
True
Within each shell, the energy of a subshell level increases with the value of the __ quantum number.
L
What is the “Pauli Exclusion Principle?”
A quantum-mechanical concept, which stipulates that each electron state can hold no more than two electrons that must have opposite spins.
When all the electrons occupy the lowest possible energies in accord with the foregoing restrictions, an atom is said to be in its ______.
Ground State
What does the electron configuration describe?
A model that represents the manner in which electron states are occupied. For example, the electron configuration of Helium is 1s^2.
Valence Electrons are the electrons that
Occupy the outermost shell.
Rows on the PT are called?
Periods
As a general rule, electronegativity increases in moving from ___ and ___ on the PT.
Left to right and bottom to top.
When atoms are brought together what two forces act?
Attractive and repulsive forces.
The minimum in the net energy curve corresponds to what?
The Equilibrium spacing R_0
The bonding energy corresponds to what on the Interatomic Separation vs Potential Energy Graph? What is the physical interpretation of this observation?
The minimum value on the curve. This value of energy represents the amount needed to separate the two atoms by an infinite distance.
For large bonding energies, what four physical characteristics are usually present?
- High melting points
- Solid at room temp
- High modulus of elasticity
- Low coefficient of thermal expansion
“Henry Sang High & Low”
Low bonding energies usually result in what physical state?
Gaseous.
T or F
Intermediate bonding energies usually result in liquids?
True
The mechanical stiffness of a material is dependant upon?
Explain why some materials are stiff while others are not with respect to the first question.
The shape of its interatomic spacing vs force curve.
The slope for a relatively stiff material will be steep; slopes are shallower for more flexible materials.
What are the three primary bonds in solids?
Ionic
Covalent
Metalic
Ionic bonding is found between what types of elements?
Metals and non-metals.
In ionic bonding which element gives up electrons?
The metals give up valence electrons to the non-metallic elements.
Extra notes: In the process, the new molecule acquires a noble gas electron configuration and a net charge.
Attractive forces in ionic bonding are ____.
Couloumbic
Covalent Bonding is found between materials whose atoms have
Small differences in electronegativity.
Extra notes: These atoms are close on the periodic table.
In Covalent Bonding, electrons are ____.
Shared.
T or F
Ionic bonding is directional?
False
T or F
Covalent bonding is directional?
True
T or F
Most materials that are covalently bonded are insulators or in some cases, semiconductors?
True
What is bond hybridization?
The mixing (or combining) of two or more atomic orbitals with the result that more orbital overlap during bonding results. Commonly occurs in carbon and other non-metallic substances.
Extra info: Directional in nature.
Describe the motion of electrons in metallic bonding?
They’re free to move between atoms that constitute the metal.
T or F
The metallic bond is non-directional?
True
Secondary Bonding (Van der Waal) forces result from what?
Molecular dipoles.
Extra Notes: The bonding results from the coulombic attraction between the positive end of one dipole and the negative region of an adjacent one.
With respect to secondary bonding, dipole interactions occur in what three scenarios?
- Induced Dipoles
- Induced dipoles and polar dipoles
- Polar dipoles
Hydrogen bonding is a type of ____.
Polar molecule bonding.
Describe hydrogen bonding.
Hydrogen bonding occurs between molecules in which hydrogen is covalently bonded to Fluorine, Oxygen, or Nitrogen.
In mixed bonding, the degree of either bond type depends on___.
The relative positions of the constituent atoms on the periodic table.
Extra Notes: If the substance is primarily composed of materials that are close on the PT (similar electronegativities) the material will be covalent dominant. If the opposite is true the material will be ionic dominant.
A crystal’s structure is analogous to…
How atoms are arranged in a crystal.
Atomic structure is analogous to…
How atoms are shaped or bonded.
What is morphology?
The study of how a crystal is shaped (e.g. micro/macro-structure).
In a neutral species, the number of protons equals the…
Number of electrons.
Give the letter designation for the principle shells 1 to 4 in that order.
1 = K 2 = L 3 = M 4 = N
Kangaroos Like Margarita Nights
A smaller principal quantum number equates to a ____ energy level.
Lower.
Within each shell, the energy of a subshell level increases with the value of the___.
l*QN
T or F
With respect to bonding forces, the difference between bond types depends on how electrons behave when two atoms are put near each other.
True
T or F
Materials with large bonding energies have:
1. Deep and Narrow Troughs on their graphs of interatomic spacing vs Force diagrams.
2. Low coefficients of thermal expansion.
True to both statements.
T or F
In ionic bonding, the electronegative metals give up their valance electrons to the non-metallic electropositive atoms?
False.
The electropositive metals give up their electrons to the electronegative non-metals.
T or F
When ionic bonding is complete, materials tend to be non-conductors of electricity in crystalline form but will conduct in liquid form?
True
T or F
Covalent bonds form between atoms that are close on the periodic table and have relatively similar electronegativities.
True
T or F
Most covalently bonded materials are electrical insulators, and in some special cases are semiconductors.
True
T or F
In metallic bonding, the bond is non-directional and atoms are shared as in covalent bonding.
True
T or F
In secondary bonding forces, there is a transfer of electrons such as in ionic bonding?
False
Atoms do not share electrons in secondary bonding. Rather, the sources of attraction between the two are couloubic in nature and results from dipole attraction.
