week材导

Introduction to Materials
(Part I-4)
Sep. 20, 2012


Module 2 Nature & Structure of Materials
2.1 Nature 2.1.1 Internal structure
ü Fundamental concepts ü Atomic structure
- concepts on nucleus & electron ü Molecular structure & bonding
- concepts on molecules - primary & secondary bonding


Internal structure: Concepts
1. Matter 2. 4 physical states 3. Mass & Weight
solid liquid gas plasma
4. Element
5. Compound
6. Polymers/Monomers
7. Molecules


2.1.1.1 Atomic Structure Page 45
I. Atom-basic building blocks of matter
√ the smallest particle of an element that possesses
the physical & chemical properties of that element
√the smallest particle (10-10 m) of an element that
can enter into a chemical change
√2 or more atoms are joined by covalent bonds,
forming the unit of matter called molecule
An element is a substance that cannot be broken down any further by chemical reaction.
nucleus (protons, neutrons) Atom
electrons


Atomic Structure Page 45
l atom has a dense center nucleus, containing protons & neutrons
+charge Proton
Nucleus
uncharged Neutron 原子核
l electrons are moving around the
Electrons
－charge
center in circular or
elliptical orbits
The planetary model


Protons & Neutrons Page 45
l A proton carries a positive electrical charge equivalent to the negative charge on an electron.
l Neutrons are uncharged particles in the nucleus with a mass nearly equal to the proton’s mass.
l Protons and neutrons are referred to as nucleons (核子) (protons + neutrons = nucleus)
*nucleus (single), nuclei (pl.), nuclear (adj.); nucleon


Fundamental concepts on atoms
1. Atomic number，Z (原子序数)
Page 45, 46
-the number of protons in the nucleus
2. Isotope 同位素 -atoms of an element with the same number of protons, but different numbers of neutrons -have the same chemical properties -differ only in mass
3. Mass number of nucleus, A (质量数) -the total number of protons & neutrons in the nucleus


Page 46
Concepts on Atoms
4. Average atomic mass (or relative average atomic mass): -express the mass relative to 1/12 the mass of a C-12 atom (defined as An atomic mass unit, u); -has no unit


Standard notation for expressing the composition of nucleus
Page 47
X: the chemical symbol of the element A: mass number, upper left superscript Z: atomic number, lower left subscript
质量数 原子序数


Isotopes 同位素
l Hydrogen
Page 45
1P
1P
1N
1P 2N
A=1 Protium 氕
A=2 Deuterium 氘
A=3 Tritium 氚
l Radioactivity 放射性:
A= mass number
√the spontaneous disintegration of a nucleus,
giving off a particles, electrons, or g rays.


Atomic structure
Proton n Atom Nucleus Neutron nucleon
Electron
1. Atomic number, Z
n Concepts 2. Isotope
3. Mass number, A
4. (relative) average atomic mass


Electrons
Page 47
electrons surround the nucleus
1. Valence electrons
价电子
ü Definition: electrons that occupy the outermost ring
or shell (电子壳层) from the nucleus
ü Valence electrons control the chemical properties of an element
2. Valence 化合价
ü Definition: valence is the capacity of an element to combine with other elements
e.g.: H2O: O is said to have a valence of -2


Electrons: Concepts
3. Ionization 电离 ü the process of pulling
away/removing valence electrons from a balanced or neutral atom (equilibrium中 性)
Page 47
Cation 阳离子 Anion 阴离子


Electrons: Concepts Page 53
4. Ionization potential 电离势/能
ü the energy required to accomplish ionization, to cause the loss of a valence electron
ü the 1st ionization potential is a measure of the energy needed to remove the 1st electron from the atom in its ground or equilibrium state (基态,平衡态)
ü the lower the ionization potential, the easier to lose electrons, the greater the metallic character
Q? Metallic vs. nonmetallic elements,
which group loses electrons easily?
ionization potential vs. electronegativity?


Electrons: Concepts Page 53
5. Electronegativity 电负性 (0～4.1)
-the degree to which an atom attracts electrons √nonmetallics are the most electronegative elements
-accept electrons to produce negative ions (anions); √produce positive ions-electropositivity 正电性 √groups VIB & VIIB contain the most
electronegative elements, with a value of 3.98 for fluorine (F)


Page 53
Electrons: Concepts
6. Electron affinity电子亲合力/能/势 - a measure of the attraction between the electron & nucleus ü the higher the electronegativity value for an element, the greater is the ability of that element to attract electrons to itself
Q? electron affinity vs. ionization potential vs.
electronegativity.


Electronic structure Page 48
A. Classical theory
polymer: chainlike
-atom with its electrons having wavelike and particlelike characteristics
l Orbitals (轨道), subshells (亚壳层), sublevels
-are used to describe the locations of electrons within
the energy level
l An orbital can be occupied by 1 electron or
by 2 paired electrons only
－s orbital: spherical shape －p orbital: dumbbell shapes －d orbital: 4-leaf clover shape
(四叶苜蓿 muxu)


Page 48
Electronic structure
B. Quantum mechanical theory 量子力学
-the position of electrons in relation to the nucleus of an atom must be described in terms of probability distribution 概率分布
ü 4 Quantum numbers - to characterize an specific electron
-the principal quantum number n -the 2nd quantum number l -the 3rd quantum number ml -the 4th quantum number ms


Orbits (轨道)
Page 49
l Shells (层) or principal energy levels (能级) are specified by a quantum number (量子数) n, where n=1 through 7 or K, L, M, N, O, P, and Q.
l 1-7 or K-Q: from the closest level to the nucleus to the outmost.


Orbits
Page 49
Orbits (n): Orbitals, subshells, sublevels, to describe the locations of electrons within the energy level, specified by a quantum number l (s, p, d, f)


主量子数
轨道角动量量子数 磁量子数 自旋角动量量子数
Page 49


Q?
Page 50
How do electrons fill in their subshells?
3 Basic rules (electron configurations 电子排布)
1. Electrons occupy their subshells in such a way as to minimize the energy of the atom
Principle of minimum energy
2. Only 2 electrons having opposite spins may exist in the same orbital
Pauli exclusion principle
3. Electrons initially occupy orbitals (not being filled, equal energy) singly (parallel electrons) Hund’s rule = tend to have as many unpaired electrons as possible!
configuration vs. conformation


Page 50
l The maximum number of electrons at any energy level is determined by the relationship 2n2 (n = energy level)
Question?
How many electrons are there in the M energy level ?


Octet rule (the rule of eight) Page 50
八隅规则, 八角定则
l Some atoms have the tendency to build up the number of electrons in their levels to 8
√Once they arrive at 8, the next one goes into the next higher level
l atoms having only 1 electron in their outermost energy level are extremely reactive, they tend to lose their electron
e.g. lithium, sodium
Question?
Atoms lacking only 1 electron in their outermost energy level? (Cl)
To obtain 1 electron.


Nonmetal & Metal
l Nonmetal
Page 51
-acceptor of electrons
-O (8O, 1s2, 2s2, 2p4), needs 2 electrons
● Metal
-Al (13Al, 1s2, 2s2, 2p6, 3s2, 3p1), need 5 electrons to keep stable
- Sodium (Na) √ready to lose 1 electron


Electrons
n Concepts on electrons
ü Valence electron & valence ü Ionization & ionization potential ü Electronegativity ü Electron affinity
n Electronic Structure
ü orbits & quantum mechanics ü rules for filling electron
(能量最低原理,Pauli不相容原理,Hund规则)
ü electron configuration


Page 51
Inert/ inactive
III. Periodic Table
p arrange the elements in order of increasing atomic number, which usually matches the order of increasing atomic mass
lanthanide
actinide
Periods
Groups


Periodic Table of elements
(元素周期表)
l Horizontal rows: periods (周期)
Page 52
l Vertical columns: groups (族);
numbered in two different ways,
-only the main groups are numbered, Roman numerals I-VIII.
-transition element (过渡元素) groups are also numbered, Arabic numbers 1-18.


Page 52
√atomic number increases
3 period


Page 52


Page 52 (Noble gases)惰性气体
过渡元素
Page 52
d (lan; 58(lan; 58--71)
(a; 90(a; 90--103)
d
f f
f
Periodic Table Page 52, 53 l Metals
üwith the exception of ü
ü
l Nonmetals
ü
ü
ü
Page 52, 53
Metalloids?
Q ?
Page 52, 53 Metalloids (semimetals)准,类,半金属
Ø
conduct
Ø
brittle
-poor conductors
Still open to discussion;
B, Si, Ge, As, Sb, Te, Po, At?
硼、硅、锗、砷、锑、碲、钋、砹?
2.1.1.2 Molecular structure & bonding
Atoms
join together
to form
Page 53
Molecules
Compounds
combine to form
Q ?
How are molecules & compounds formed ?
Chemical bonding
Page 54 Chemical bonding化学键
l Definition:interaction
attraction repulsion oppositely
similarly
l
outermost
(valence electrons)
Types of bonding
Bonding
Primary
Secondary Vander Waals forces
主化合键,
主价键次化合键Page 54范德华力
bonding
co valent, ionic,
metallic bonding
strong
weak atomic bond,electric di pole,
Polar 极性molecule,hydrogen bond
weak
bonding
, 次价键
Various types of bonding
Points:
l solely l predominate l Page 54
mixed bond types Polymers: covalent bond + hydrogen bond
In ceramics?
Covalent bonding Page 54
share
Covalent bonding
Saturated HCs
饱和的
不饱和的
Page 55
Unsaturated HCs
Alkanes 烷烃 Alkenes 烯烃 Alkyne 炔烃 methane CH4 ethylene C2H4 acetylene C2H2
l Hydrocarbons (HC): contain only H & C elements
碳氢化合物
芳香的
l Aromatic: contain a benzene ring/cycle, with similar properties to those of benzene toluene 甲苯; dimethylbenzene (xylene) 二甲苯


Page 56
Ionic bonding (Electron swapping)
l elements actually swap (交换swop) or
transfer electrons to other elements
l elements having outer electron levels are
almost full or almost empty tend to gain
(negative ion: anion ) or lose electrons
(positive ion: cation )
swap
swop
stransfer


A classic example of ionic
bonding
Valence
-
-
shell
-
-
-
-
-
-
-
P11
Na
-
-
--
--
-
--
P17
Cl
--
-
--
-
-
Sodium (Na) Cation
NaCl
-
-
-
-
Chlorine (Cl) anion
sodium chloride


Page 57
Metallic bonding/electron swarming 电子云
l metal atoms (containing 1, 2, or 3 covalence electron) lose their weakly held valence electrons and become positive ions (cations)
l free or delocalized electrons (离域电子) can move in three dimensions (electron cloud)
Q.
Metallic bonding: swarming; Ionic bonding: ? swap/swop, transfer Covalent bonding: ? share


Types of bonding
Bonding
Page 54
Primary Secondary bonding bonding
strong
covalent, ionic,
metallic bonding
weak
weak atomic bond, electric dipole, polar molecule, hydrogen bond


Secondary bonding Page 57
l Vander Waals bonds, weaker forces of attraction between atoms and between molecules
-created by the interaction of electrical charge distribution between molecules
l Nonpolarized (非极性) molecules
-each atom shares the bonding electrons equally
-
-
P-9
-
--
-
P-9
-
-
-
F-
-
---
F-
-
--


Polar molecules/Electron dipoles
极性分子
lthe electrons are HCl
not shared equally,
电偶极
Center of negative charge
charges are polarized; i.e. +, charges are
＋ －Polarized
localized within molecules
Center of
Page 58,59
positive charge
Example: hydrogen bond, the strongest of the secondary bond


Molecular structure & bonding
■ Chemical bonding Bonding
-definition
-types Primary bonding
strong
Secondary bonding Vander Waals
forces
weak
covalent, Ionic,
metallic bonding
weak atomic bonds electric dipoles polar molecules hydrogen bond


2.1.2 Solid State
Page 59
Atoms, Elements
join together Chemical to form bonding
Molecules combine
Q?
to form
What state can a compound exist in?
Compounds
Four physical states of matter?


Solid State
Page 59
★ A solid is a sample of matter that has a fixed volume or size & a fixed shape
-its shape retains indefinitely without any need to confine it
-do not flow like liquids nor do they expand like gases
★ The attractive forces between atoms in a
solid were much greater than that between atoms in a liquid or gas
Indefinitely (时间)不确定的, 无限期的

。