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Material Science > Ch 2 > Flashcards

Ch 2 Flashcards

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0
Q

What is most of an atom comprised of?

A

Most of the atom is composed of empty space because the electrons travel extremely far away from the nucleus

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1
Q

Are atoms devils able and visible?

A

Yes they are. You can see an electron with a piezoelectric tube with electrodes

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2
Q

What are protons, and neutrons made of? And what is its size?

A

They are both made of quarks which have the size of 10^-16 cm

Objects made of quarks are called hadrons. Both of these are composed of 3 quarks and therefor called baryons(a subclass of hadrons)

Electrons are leptons and not known to be made up of any sub particles.

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3
Q

About how much lighter are electrons than protons and neutrons?

A

About 2000 times lighter

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4
Q

What is the smallest particle that will retain an objects chemical properties?

A

An atom

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5
Q

How is the atomic number calculated?

A

By summing up the number of protons and number of electrons

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6
Q

How is the atomic mass found?

A

By summing the mass of the protons, and the mass of the neutrons

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7
Q

What proportion of the mass of carbon is one amu equal too?

A

1/12 the mass of carbon

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8
Q

What are the units for (average) atomic weight?

A

Amu/atoms and g/mol

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9
Q

What is an isotope?

A

Atoms with the same atomic number, but a different atomic weight because of a different number of neutrons.

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10
Q

What is the (average) atomic weight?

A

The average atomic mass of all naturally occurring isotopes

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11
Q

How many atoms are in one amu?

A

6.022x10^23 or avrogadros number

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12
Q

Why are atomic weights generally not integers?

A

Because the atomic masses of atoms are normally not integers

The atomic weight is taken as the weighted average of all naturally occurring isotopes

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13
Q

How much do electrons, protons, and neutrons weight?

A

Electrons weigh 9.11x10^-31 kg

Protons and neutrons weigh 1.67x10^-27 kg

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14
Q

What are the group 1 and group 2 elements called? What about the d block elements? P block? Group 7 elements? Group 8 elements? F block elements? What are the metalloid elements?

A

Group 1= alkaline metals
Group 2= alkali earth metals

D block = transition metals

P block = non metals

Group 7= halogens

Group 8= noble gasses or inert gasses

F block= rare earth series

The metalloid include: B, C, Si, Ge, As, Se, Te

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15
Q

What is the difference between the Bohr atomic model and the schrodinger wave mechanical model?

A

The both model:
Electrons are assumed to revolve in discrete (specific distances) orbitals around the nucleus

Energies of electrons are quantized, that is electrons can only have certain values of energy.

Electrons can make quantum jumps to change energy. Higher levels of energy=absorb energy, lower levels= emit energy

Schrodinger wave mechanical model:

Position of an electron is described by the probability(pitch fork squared) distribution of electron clouds around the nucleus

4 quantum numbers are used to characterize each electron in an atom

It doesn’t say exactly where the electron is, but where the best probability of finding it is.

Electrons have both particle and wavelike characteristics

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16
Q

What are quantum numbers, and what does each one stand for and describe?

A

Quantum numbers describe size, shape, and spacial orientation of an electron probability distribution.

(N) the principal quantum

  • Designates the size and principal electron shell
  • this is the only quantum number associated with the Bohr model

(L) azimuthal quantum number

  • sometimes called angular momentum an
  • designates the subshell(the shape of the orbital)
  • l=n-1
  • have names(s,p,d,f)
  • the value l tells you how many nodes there are in the probability distribution of the orbital
  • also describes the bonding angle, direction of bond in molecules

(Ml) magnetic quantum number
-gives the number or electron orbitals and their orientations

(Ms) electron spin quantum number

  • determines the spin of the electron…either -1/2 or +1/2
  • the spin of the electron is the minimum angular momentum needed to stay stable
  • 2 electrons per orbital
17
Q

What does the Pauli exclusion principle state?

A

Each electron state can hold 2 electrons and must have opposite spins

18
Q

What does hands rule state?

A

Every orbital must be filled once in all the same direction(electrons with the same spin) before you can fill them in the other direction

19
Q

How many electrons can be held in the s,p,d,f orbitals?

A

S=2
P=6
D=10
F=14

20
Q

What is considered a ground state atom?

A

One that fills its orbitals from the first orbital (1s) and then work its way up obeying all the rules

21
Q

What is an excited state atom?

A

When an electron fills a higher orbital before a lower one, or skips an orbital

22
Q

Which properties do valence electrons determine?

A

Chemical, electrical, thermal, and optical properties

23
Q

What classification do most of the elements on the periodic table come under?

A

Most of them come under the metal classification. These are sometimes referred to as electropositive elements, because they are capable of giving up their few valence electrons to become positively charged ions.

The elements on the right side of the periodic table are called electronegative elements, because they are ready to accept negatively charged ions, or sometimes they share with other atoms.

24
Q

Why does electronegativity increase as you move up and right on the periodic table?

A

Because atoms are more likely to accept electrons if their outer shells are almost full and if they are lest shielded from the nucleus.

25
Q

What is ionic bonding?

A

A bond composed of a metallic and non metallic element.
Usually between a very electronegative ion(wants to steal electrons) and a electropositive ion(one that wants to give off electrons)

This bond is a transfer of electrons from one ion wanting to give up electrons to another ion that wants to take those electrons because both atoms want to get to full closed shells

Tend to be very non-directional in their bonding because the magnitude of the bond is equal in all directions

26
Q

What is a metallic bond?

A

Occurs when atoms have partially filled electron orbitals interacting with other atoms with similar electronegativity.

Seen in both alkali and alkali earth metals, transition metals, and in the post transition metals

These atoms have a lower overall energy, so these electrons delocalized and distribute the selfs evenly.
These electrons distribute into a sea of electrons that have metal ion cores floating in the sea. This tends to cause a lower overall energy of the system.

Occurs in metals and metal alloys

27
Q

What is a covalent bond?

A

Occur when atoms share electrons in order to get a full closed shell. These tend to be very strong bonds and very localized.

Usually group 4 materials or surrounding materials(usually occurs with adjacent elements-remember covalent=close)

Hybridization occurs when you get an overlap from bonding between two or more orbitals. These hybrid orbitals are directional in nature.

28
Q

What is van der walls bonding?

A

Intermolecular bonding between adjacent molecules or atoms that have already filled their shells.

Extremely weak compared to intramolecular bonds

Caused by interactions between dipoles( induced dipoles, induced dipoles and polar molecules, and between two polar molecules

These bonds are in everything, however they are weak enough to ignore unless they are inert gases, or covalently bonded molecules

Hydrogen bonds are a specific type of secondary bond between n,o,f and hydrogen

29
Q

Which natural phenomenon are associated with secondary bonds?

A

Solubility, surface tension, capillary action(straw), vapor pressure, volatility, and viscosity.

30
Q

Explain how adhesives work with secondary bonds

A

They have gander walls bonds that form between two surfaces so that they adhere to one another

31
Q

What is a surfactant?

A

A compound that lowers the surface tension of a liquid

32
Q

What is a emulsifier?

A

A substance that, when added to two immiscible materials, allow particles of one material to be suspended in another(milk, mayonnaise)

33
Q

What is a desiccant?

A

A material that forms hydrogen bonds with water molecules. Is is used to remove moisture from closed containers

34
Q 
What types of bonds do:
Polymers have?
Metals? 
Ceramics?
Molecular solids?
Semi-metals?
Inter Metallics?
A 
Polymers=covalent
Metals= metallic
Ceramics= ionic-covalent
Molecular solids=van der walls
Semi-metals= covalent metallic
intermetallics=metallic-ionic
35
Q

Rank the bonds in order from weakest to largest:

Ionic, van der walls, covalent, metallic

A

Van der walls < metallic < covalent < ionic

36
Q

How are elastic modulus, melting temperature, and coefficient of linear thermal expansion related to bonding?

A 
Elastic modulus(stiffness) 
High elastic modulus= high bond strength = very stiff

Melting temperature
High bond strength = high melting point

Coefficient of linear thermal expansion(how much a material will expand or contract)

The larger the coefficient, the more it will expand, while the smaller the coefficient, the less it will expand

High bond strength = low coefficient and vise versa

37
Q

What is the order of bond strength in material classes from low to high?

A

Polymers < metals < ceramics

38
Q

What is the order of elastic modulus in materials from low to high?

A

Polymers < metals < ceramics

39
Q

What is the order of melting temperatures of the materials from low to high?

A

Polymers < metals < ceramics

40
Q

What is the order of materials from the smallest to the highest coefficient of linear thermal expansion?

A

Ceramics < metals < polymers

Material Science (2 decks)

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