Chapter 2 Review

Question 1

What are the 5 length scales we use to analyze material structure?

Think dimensional categories and respective size

Answer 1

1. atomic structure [0.1 nm]
2. short & long range atomic arrangements
   [short: 1 to 0.1 nm | long 10 nm to 1 cm]
3. nanostructure [1 to 100 nm]
4. microstructure [100 to 100,000 nm | grain size]
5. macrostructure [100 m]

Question 2

What is electronegativity?

Answer 2

An atoms affinity for electrons. [ie the tendency for an atom of a given chemical element to attract shared electrons when forming a chemical bond. An atom’s electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus. The higher the associated electronegativity, the more an atom or a substituent group attracts electrons.]

Basically, it’s electron piracy. One atom stealing from those below it

Not applicable to Noble Gases and does weird things with transition metals. Also, Gold is the most electronegative metal for no reason.

Question 3

What are valence electrons?

Answer 3

The number of electrons in an atom that participate in chemical reactions
Dependant on immediate environment surroundings
(eg Maganese may have valence of 2-7 depending on surroundings!)

Question 4

How does electronegativity increase across the periodic table? (what factors affect its value?)

Answer 4

Increases left to right, down to up.
Increased radius causes decrease
More outer shell filled causes increase

Question 5

Why do we care about atomic bonding?

Answer 5

Because they reveal trends for macroscopic mechanical properties. They don’t out right determine properties, but they play a substantial role.

Question 6

What kinds of atomic bonding exist?

Answer 6

Metallic Bonds
Covalent Bonds
Ionic Bonds
Van der Waals Bonds (2nd-ary)

Question 7

What characterizes metallic bonding?

Answer 7

Weakest of the primary bonds
A large factor in metals ductility
Electrons are shared
“Sea of electrons”
Non directional bonds
Electrons are happy everywhere

Window open. Cold breeze. Curls up. don’t want to move.

Think: Heavy metal band of angsty teenagers who pitch in there life savings to do stuff. They have no direction in life and kind of just float around, but they have strong relationships within the ‘tribe’. Very emotional and can get heated and electric pretty quickly.

Question 8

What characterizes covalent bonding?

Answer 8

Very Strong
Valence electrons shared between 2 atoms
Prevalent in stochiometric compounds like intermetallic materials
not really conducive to conductivity- since electrons are tied up

Think: The highschool sweet hearts who got married. Share everything. Almost inseperable.

Question 9

What characterizes ionic bonding?

Answer 9

Very Strong
Valence electrons ‘donated’/stolen through electronegativity
Atoms that give/take electrons have ionic charges-which bond them
Prevalent in stochiometric compounds like intermetallic materials

Na and Cl&raquo_space; Na+ and Cl-

Think: Trojan Horse. Gives electron but once you take it, you’re bonded. no escape.

Question 10

What characterizes Van Der Waal Forces?

Answer 10

Secondary Forces
Relatively Weak
Polarity of Molecules Causes them to be attracted to the sides of other molecules opposite charge.
Crucial for plastics which are held by covalent bonds otherwise
Play a role in determining boiling points and surface tension of liquids

Question 11

What are London Forces?

Answer 11

A type of Van Der Waals force
Due to a polerized atom polerizing a neutral atom causing them to have the slightest charge difference which leads to a small electrical force

Think London mafia dude tazers a stranger who then gets Stockholms & doesn’t want to leave

Question 12

What are Keesom interactions?

Answer 12

Similar to London Force but on molecular level
Between permanently polarized molecules (not induced)
Bond due to polerization
Given 2 water molecules, on the first molecule electrons on oxygen concentrate away from the hydrogens on the second water molecule. Thus, they establish a weak bond due to electrical potential.

Typically called Hydrogen Bonds

Question 13

What is a stoichiometric compound?

Answer 13

A stoichiometric compound maintains fixed and precise ratios of elements expressed in whole numbers.

Question 14

What is an intermetallic material?

Answer 14

Compounds formed from 2 or more metals

Question 15

How are equilibrium interatomic distance and the force neccesary to change them related to Young’s Modulus?

Answer 15

Youngs modulus is a measure of stiffness
The more force it takes to cause a given atomic displacement the more stiff a material is and thus the greater Youngs modulus it will have.

Question 16

How does a materials atomic bond strength affect it’s behavior under thermal expansion?

Answer 16

Materials that have stronger bond forces will be more resistive to thermal expansion that materials that have weaker bond forces.

Question 17

What are alltropes?

Answer 17

Allotropes are two or more forms of the same element that differ in their physical and sometimes chemical properties

Diamond and Graphene

Question 18

How are grain size and metallic strength related?

Answer 18

Generally, smaller grain size leads to stronger metals

Question 19

What does the atomic number tell us?

Answer 19

The number of protons in the atom

Question 20

Why is Avogadros number 6.022x10^23?

Answer 20

Its the inverse of 1 atomic mass unit
It is defined as such to relate the atomic mass number of atoms to grams.

example:
Nitrogens atm is 14
1 atm is 1.6605x10^-24 grams/atoms
thus, 14 x 1.6605x10^-24 grams /atoms x (# atoms) = 14 grams
The # atoms required to satisfy this desired outcome is 1 mole, which is the inverse of 1.6605x10^-24

Question 21

What is spectroscopy?

Answer 21

The science of identifying elements in a material due to the unique energy signatures between energy levels in the electron clouds.

Question 22

What are the 4 quantum numbers that encapsulate the energy levels of electrons?

Answer 22

1. Principal Quantum number [n]
2. Azimuthal (Secondary) Quantum number [l]
3. Magnetic Quantum number [m_subl ]
4. Spin quantum number [m_sub s ]

Question 23

How many valence electrons does Aluminum have?
And why do we care?

Answer 23

Aluminum has 3 outer electrons in its outer s & p levels.
We care because the atomic bonding and behavior of Aluminum are determined by how these 3 electrons interact with surrounding atoms.

Question 24

What give metals proclivities towards mixed or pure bonds?

Answer 24

Electronegativity. The greater the difference in electronegativity the greater likelyhood of mixed bonds (metalic and ionic). If the electronegativity is equal, we’d expect primarily metallic bonding to occur.

Question 25

What give ceramics and semiconducting compounds proclivities towards mixed or pure bonds?

Answer 25

Electronegativity. The greater the difference in electronegativity the more likely for pure ionic bonding to occur. The less different, the more likely for mixed bonds to occure (ionic and covalent)

Question 26

What is the coeeficient of thermal expansion and what does it tell us?

Answer 26

CTE is the fractional change in linear dimension of a material per degree of temperature. Smaller CTE means less deformation for a given temperature change. Larger CTE means more deformation for a given temperature change. CTE is ‘proportional’ to deformation.

Question 27

How does THERMAL & ELECTRIC CONDUCTIVITY relate to atomic bond types?

MECHANICAL PROPERTIES

Answer 27

stronger bonds = greater thermal conductivity
increased heat vibrates the atomic structure.
The more rigid the bonds are the more efficiently they can transfer heat

stronger bonds = lesser electric conductivity
Stronger bonds require electrons to be held hostage.
Thus, there are less (if not none) electrons to ‘flow’

Thus, thermal conductivity is inversly related to electrical conductivity (?)
A great example of this is diamond (covalent bonds galore).
Best thermal conductivity and extremely poor electrical conductity.

Question 28

Why does there exist an equilibrium interatomic spacing in metals?

Answer 28

Because the nuclei (which are positivly charged) are attracted to the electron cloud (negativly charged), but they are repelled by the other nuclei. Thus, there is a constant tug-of-war going on and as the nuclei settle into positions, they establish a lattice of equilibrium distances.

Question 29

How do disruptions in equilibrium interatomic spacing affect dislocation motion?

Answer 29

Disruptions in equilibrium interatomic spacing will make it more difficult for dislocations to move and thus affects the materials properties, generally making it stronger.

Question 30

What is binding energy?

Answer 30

The amount of energy required to create or break the bond

Question 31

Is Young’s Modulus sensitive to changes in microstructure?

Answer 31

Not Really.

Young’s has been hardened over many centuries.
It’s not very sentimental; quite rough around the edges.
Young’s knows that microstructure will do what microstructure will do.
All Young’s can do is stiffen his lip, and keep marching forward.