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Materials Science > Topic 2- Structure and Bonding > Flashcards

Topic 2- Structure and Bonding Flashcards

1
Q

What are the four main features of electrons in Niels Bohr model of the atom?

A
  1. Negative.
  2. Orbit nucleus in discrete orbital shells.
  3. Quantized positrons.
  4. Specific energies.
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2
Q

What was Niels Bohr’s model later refined to?

A

Wave-mechanical model.

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3
Q

Which energy state is filled first?

A

The lowest.

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4
Q

What do principal quantum numbers tell us? (K, L, M, N, O)

A

The distance from the nucleus. The principal quantum numbers represent different layers of electrons.

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5
Q

What does the second quantum number, I, tell us? (s, p, d, f)

A

Shape of the subshell. The shape affects the number of electrons.

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6
Q

What does the magnetic quantum number, mI, tell us? (-2, -1,0, 1, 2)

A

The orientation in space.

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7
Q

What does the spin quantum number, mS, tell us? (+1/2, -1/2)

A

The spin on the electron.

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8
Q

What is an atom and what does it consist of?

A

Smallest piece of an element.

Consists of protons, neutrons and electrons.

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9
Q

What are the maximum number of electrons in each subshell? (s, p, d, f)

A

s orbital = 2
p orbital = 6
d orbital = 10
f orbital = 14

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10
Q

What creates a stable electron configuration (unreactive)?

A

Complete s and p subshells.

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11
Q

What is the electron configuration of helium?

A

1s^2

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12
Q

What is the electron configuration of neon?

A

1s^2, 2s^2, 2p^6

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13
Q

What is the electron configuration of argon?

A

1s^2, 2s^2, 2p^6, 3s^2, 3p^6

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14
Q

What is the order in which shells fill up?

A

1s-2s-2p3s-3p4s-3d4p5s-4d5p6s-4f5d6p7s-5f6d7p

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15
Q

Which Russian chemist and inventor is the periodic table credited to?

A

Dmitri Mendeleev (1834-1907).

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16
Q

What determines the observed properties of elements?

A

Their atomic structure.

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17
Q

What is the atomic (top) number?

A

The number of protons/ electrons.

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18
Q

What is the atomic mass?

A

The number of protons + neutrons.

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19
Q

Why isn’t the atomic mass a whole number?

A

Isotopes which have a different number of neutrons.

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20
Q

How are elements grouped in the periodic table?

A

Into columns that have a similar number of valence electrons and thus properties.

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21
Q

What is relative atomic mass?

A

Mass of 1 mol (6.02x10^23 atoms).

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22
Q

What is an atomic mass unit?

A

1/12 mass of a carbon-12 atom (98.9% of carbon atoms).

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23
Q

What are valence electrons?

A

The electrons within the outer shell so that will react.

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24
Q

What are electron donors and which side of the periodic table are they found on?

A

Metals. Left.

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25
What are electron acceptors and which side of the periodic table are they found on/
Non-metals. Right.
26
How can atoms achieve a full outer shell? Why do they want a full outer shell?
Through bonding. Lower energy thus more stability.
27
What are the three types of primary bonding?
Ionic, covalent and metallic.
28
What are the two types of secondary bonding?
Van der Waals and hydrogen.
29
What happens during an ionic bonding?
An electron is transferred in a chemical reaction from a metallic to a non-metallic element.
30
What does ionic bonding produce? Give four examples.
Compounds of metallic and non-metallic elements. 1. Sodium Chloride (NaCl) 2. Magnesium Oxide (MgO) 3. Calciumm Floride (CaF2) 4. Caesium Chloride (CsCl)
31
What ions are formed during ionic bonding?
The metallic atom becomes a positive ion and the non-metallic element becomes a negative ion.
32
How are ions held together?
Electrostatic attractive forces (unlike charges attract each other).
33
Is ionic bonding directional or non-directional?
Non-directional.
34
How strong is ionic bonding?
Relatively strong.
35
How is a crystalline structure created?
Each ion surrounds itself with ions of the opposite charge creating a giant ionic crystal.
36
What type of materials are typically ionically bonded?
Ceramics e.g. Alumina, Al2O3
37
Do ionically bonded materials typically have high or low melting points?
High e.g. 2200 degrees Celsius.
38
Do ionically bonded materials typically have a high or low elastic modulus?
High, so are stiff e.g. E=400 GPa.
39
Are ionically bonded materials brittle or tough?
Brittle (difficult for atoms to slide/rearrange)
40
What are the insulating properties of ionically bonded materials?
Thermal and electrical insulators (no free electrons).
41
In what situation will an electric current flow in a ionically bonded material?
If the crystal is dissolved in water or melted then the ions are free to move.
42
What is covalent bonding?
A new substance is created with a stable electron configuration formed by sharing electrons between atoms. The shared electrons occupy the space between the two atomic nuclei and belong to both atoms.
43
Which elements are usually included in covalent bonding?
Those on the right hand side of the periodic table.
44
Give four examples of covalent bonding.
1. Hydrogen, H2 2. Water, H2O 3. Diamond, C 4. Silicon Carbide, SiC
45
What is a polymer?
Chain of carbon atoms.
46
Is covalent bonding directional or non-directional?
Directional, e.g. CH4 is a tetrahedron shape - 3-sided-based pyramid.
47
Is covalent bonding strong or weak?
Very strong.
48
What materials are typically formed by covalent bonding?
Non-metal compounds, often polymers, glasses and ceramics. Some elemental solids (Si, C (diamond))
49
Are covalently bonded materials more or less dense than those ionically or metalically bonded materials?
Less dense - directional bonding makes it hard to pack atoms.
50
Do covalently bonded materials have a high or low elastic modulus?
High, so stiff. E approx. 1000GPa.
51
What is an example melting point of a covalently bonded material?
3550 degress Celsius.
52
Are covalently bonded materials tough or brittle?
Brittle (strong, directional atomic bonds)
53
Are covalently bonded materials insulators or conductors?
Thermal and electrical insulators.
54
Which materials don't match covalent bonding properties? Why?
Polymers have a low stiffness and melting point. The bonds holding the molecule together are very strong but Van der Waals force which attracts neighbouring molecules is much weaker (weak bonding between chains).
55
How does metallic bonding occur?
Metals and alloys have a low number of valence electrons, these become delocalized so are no longer bound to any atom.
56
What happens to the delocalized electrons in metallic bonding?
They drift throughout the metal forming a sea of "delocalised electrons" around the atoms.
57
In metallic bonding, why do the atoms become positive ions?
They have lost one or more electrons.
58
Where does the very strong electrostatic attraction occur in metallic bonding?
Between the metal ions and the sea of negative electrons.
59
Is metallic bonding directional or non-directional?
Non-directional.
60
How strong is metallic bonding?
Intermediate strength.
61
Give two examples of metals which metallically bond?
Aluminium, Al and Tungsten, W.
62
What are the intermediate melting points of the metal examples given?
Aluminium - 660 degrees Celsius. | Tungsten - 3410 degrees Celsius.
63
Do metallically bonded materials have high or low density?
High - close packing of atoms.
64
Are metalically bonded materials conductor or insulators?
High electrical and thermal conductivity due to free electrons.
65
Why are metallically bonded materials ductile?
Planes of atoms can slide over each other.
66
What does Van der Waals bonding do?
Hold neighbouring molecules together.
67
How does Van der Waals bonding occur?
Small negative and positive regions occur on some molecules and can attract neighbouring molecules, due to atomic or molecular dipoles (assymmetric molecules).
68
Where do dipoles occur?
In inert gases or between covalently bonded molecules.
69
When do fluctuating dipoles occur? Give one example.
Due to asymmetric electron clouds. Liquid H2.
70
How do permanent dipoles occur? Give an example.
These are molecule induced e.g. in polymers. Liquid HCl.
71
Give five characteristics of metallic bonding.
1. Bonding is directional and weak. 2. Materials are usually polymers (bonding occurs between covalent chains). 3. Low stiffness (E<5GPa). 4. Low melting point (<400 degrees Celsius). 5. Very ductile.
72
What is the reason for water being a liquid at room temperature?
Hydrogen bonding.
73
How does hydrogen bonding occur?
From the interaction and delocalisation of hydrogen electrons.
74
How do atoms interact at a large distance?
Little interaction.
75
What forces occur as atoms approach? What do these depend on?
Attractive force, Fa, depends on type of bonding/valence. | Repulsive force, Fr, from the overlap of electrons.
76
What is the net force as two atoms approach?
Fn = Fa + Fr
77
When does equilibrium separation (ro) occur?
When Fa + Fr = 0.
78
What creates the forces between atoms approaching?
The energy potential.
79
What is force the differential of?
Energy.
80
What does energy equilibrium reveal?
Fundamental properties of materials.
81
How does increasing E0 affect melting temperature?
Tm is larger if E0 is larger.
82
How does E0 affect the elastic modulus?
E is larger if E0/curvature is larger.
83
How can we calculate equilibrium separation?
Calculate r when Fn = 0.
84
How can we calculate binding energy E0?
Calculate En when r=r0.
85
How are ceramics bonded? Is the bond energy large or small? What properties does this give them?
Ionic and covalent. Large. Large Tm and large E.
86
How are metals bonded? Is the bond energy large or small? What properties does this give them?
Metallic. Variable. Moderate Tm and moderate E.
87
How are polymers bonded? How does this affect bond energy? What properties does this give them?
Covalent and secondary. Secondary bonding dominates - weak. Small Tm and small E.
88
How is magnesium oxide (MgO, ceramic) bonded? What is its bond energy? What is its Tm and E?
Ionic. 5eV/atom. Tm = 2800 degrees C. E = 250 GPa.
89
How is diamond (C) bonded? What is its bond energy? What is its Tm and E?
Covalent. 7eV/atom. Tm = 3550+ degrees C. E = 1000 GPa.
90
How is aluminium (Al) bonded? What is its bond energy? What is its Tm and E?
Metallic. 3eV/atom. Tm = 660 degrees C. E = 70 GPa.
91
How is tungsten (W) bonded? What is its bond energy? What is its Tm and E?
Metallic. 8eV/atom. Tm = 3410 degrees C. E = 400 GPa.
92
How is PVC bonded? What is its bond energy? What is its Tm and E?
Van der Waals. 0.5eV/atom. Tm = 210 degrees C. E = 3GPa.
93
What is strength of materials dependent on?
Defects within the material.

Materials Science (8 decks)

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