MSE 102 MATERIALS SCIENCE AND ENGINEERING ORIENTATION Structure of Solids (Atomic structure, periodic table, molecular structure, bonding) Materials Science and Engineering Çankaya University Previous Lecture
Processing
single crystal polycrystal: low porosity polycrystal: high porosity Structure
Properties
Three disk specimens of aluminum oxide
Performance
2 Previous Lecture_Structure
Investigation of Microstructures
Important applicaQons of microstructural examinaQons: •  To understand the associaQons between the properQes and structure •  To predict of the properQes of materials once establishing these relaQons •  To design alloys with new property combinaQons •  To determine whether a material has been correctly heat treated and to ascertain the mode of mechanical fracture. Previous Lecture_Structure
Relates to the arrangement of its internal structure
2 0
n m
Cu
Plate-like
Cu Z
10 r
7
Zr
Plate-like
Macroscopic
Cu10Zr7
Microscopic
Atomic
Subatomic
Why study atomic Structure and
Interatomic bonding?
Two Allotropes of CARBON
Graphite
-  Relatively soft
-  Greasy feel to it
-  Reasonably good
conductor of electricity
Diamond
-  The hardest known material
-  Poor conductor of electricity
The dispari.es in proper.es are aSributed to a type of interatomic bonding found in graphite that does not exist in diamond ClassificaQon of MaSer MaSer can be classified by two principle ways according to its physical state (gas, liquid or solid) or its composiQon (element, compound or mixture). A sample of maSer can be a gas, a liquid, or a solid. Three physical states of water are water vapor, liquid water, and ice. The molecules in the solid are arranged in a more orderly way than in the liquid. The molecules in the gas are much farther apart than those in the liquid or the solid. 6 ClassificaQons of MaSer Most forms of the maSer around us are not chemically pure so we can separate these kinds of maSer into different pure substances. A pure substance is maSer that has disQnct properQes and a composiQon that does not vary from sample to sample. All substances are either elements or compounds. Elements -­‐  Cannot be decomposed into simpler substances -­‐  Each element composed of only one kind of atom -­‐  At the present Qme 114 elements are known -­‐  The symbol for each element is enclosed in a box called periodic table 7 !
ClassificaQons of MaSer Most elements can interact with other elements to form compounds. The law of definite propor8on refers to the observaQon that the elemental composiQon of a pure compound is always the same. A pure compound has the same composiQon and properQes that does not depend on its source. Most of the maSer consists of mixtures of different substances. -­‐  Each substance in a mixture retains its own properQes and chemical idenQty. -­‐  The composiQons of mixtures can vary. -­‐  Some of the mixtures that are uniform throughout are homogeneous (such as air mix. of nitrogen, oxygen and small amounts of other subs.), the others that do not have the same composiQon, properQes and appearance throughout the mixture are named as heterogeneous (such as wood, sand, rocks). -­‐  Homogeneous mixtures are named as solu8ons as well. 8 ClassificaQons of MaSer On the molecular level 9 ClassificaQons of MaSer MaSer Is it uniform throughout? If yes If no Does it have a variable composiQon? If yes Compound If no Element Homogeneous Heterogeneous Can it be separated into simpler substances If no Pure substance If yes Homogeneous mixture (soluQon) 10 Why study atomic Structure and
Interatomic bonding?
Two Allotropes of CARBON
Graphite
-  Relatively soft
-  Greasy feel to it
-  Reasonably good
conductor of electricity
Diamond
-  The hardest known material
-  Poor conductor of electricity
The dispari.es in proper.es are aSributed to a type of interatomic bonding found in graphite that does not exist in diamond Atomic Models
Atomic Structure (Freshman Chem.) •  atom – electrons – 9.11 x 10-­‐31 kg protons 1.67 x 10-­‐27 kg neutrons }
•  atomic number = # of protons in nucleus of atom = # of electrons of neutral species •  A [=] atomic mass unit = amu = 1/12 mass of 12C Atomic wt = wt of 6.023 x 1023 molecules or atoms 1 amu/atom = 1g/mol C 12.011 H 1.008 etc. 13 The Mole A mole is defined as the quanQty of maSer that contains as many objects (atoms, molecules, or whatever objects we are considering) as the number of atoms in exactly 12 g of 12C. The number of atoms in a 12 g of sample of 12C to be 6.0221421x1023 which is named as Avogadro's number (which has a symbol of NA). 1 mol 12C atoms = 6.02 x1023 12C atoms 1 mol H2O molecules = 6.02 x 1023 H2O molecules 1 mol NO3-­‐ ions = 6.02 x 1023 NO3-­‐ ions Molar mass is the mass in grams of one mole of a substance. The molar mass (in grams) of any substance is always numerically equal to its formula weight (in amu): One 12C atom weighs 12 amu = 1 mol 12C weighs 12 g One 24Mg atom weighs 24 amu = 1 mol 24Mg weighs 24 g One H20 molecule weighs 18.0 amu = 1 mol H20 weighs 18.0 g One NO3-­‐ ions weighs 62.0 amu = 1 mol NO3-­‐ ions weighs 62.0 g The Atomic Theory of MaSer Timeline of atomic theory Democritus’ Aristotle and Plato atomos Dalton J.J. Thomson 460 BC 360 BC 1808 1897 1909 1913 1923 E. Rutherford N. Bohr Wave Mechanical 15 Democritus (460-370 BC)
•  Greek philosopher
•  Material world must be made up of tiny
indivisible particles that they called atomos.
•  The word atom comes from the Greek word
atomos meaning indivisible or uncuttable.
•  Atoms were completely solid, hard and
small particles with no internal structure and
has an infinite variety of shapes and sizes.
•  This theory was ignored for more than 2000
years!
Aristotle and Plato
•  There can be no ultimately
indivisible particles.
•  Believed that fire, earth, air
and water were the four main
elements that world was made
up of.
John Dalton (1803)
•  English instructor and natural philosopher
•  Beginning of the modern era of
chemistry.
•  Explanation of the structure of matter in
terms of different combinations of very small
particles.
Each element consists of atoms of single
unique type and can join to form chemical
compounds.
John Dalton (1803)
1.  Elements are composed of extremely small particles called
atoms.
2.  All atoms of a given element are identical, having the same
size, mass and chemical properties. The atoms of different
elements are different. Different elements have different
atomic properties such as atomic mass.
3.  Atoms of an element are neither created nor destroyed by any
chemical reactions. Chemical reactions only involve the
combination, rearrangement or separation of atoms.
4.  Compounds are formed from the combination of atoms of more
than one element. A compound always has the same relative
number and kind of atoms.
Mendelev (1869)
The periodic table was first developed by
Mendeleev and Meyer on the bases of
similarity in chemical and physical
properties exhibited on certain elements.
Mendeleev's 1871 periodic table The Periodic Table The dates of discovery of the elements •  Elements in the same column have the same numbers of electrons in their valence orbitals which leads to the similari?es among elements in the same group. •  The differences among elements in the same group arise because their valence 21 orbitals are in different shells. Today: Periodic Table of the Elements
The Structure of the Atom
Status report end of the 19th century
•  Atom is electrically neutral •  Negative charge carried by electrons •  Electron has very small mass –  bulk of the atom is positive, –  most mass resides in positive charge J. J. Thomson (1897)
•  Although Dalton had postulated that atoms were indivisible, the studies have shown a more complex structure for an atom. J. J. Thomson conducted a series of
experiments which showed that the atoms
were not indivisible….
Plum Pudding (1904): The atom as being
made up of electrons swarming in a sea of
positive charge.
Discovered the electron (1906 Nobel Prize in
Physics).
J. J. Thomson's "plum-­‐pudding" model of the atom E. Rutherford (1909)
•  Tested and disproved the Plum Pudding Model. Rutherford's experiment on the scaGering of α par?cles by metal foil •  Results:
–  Majority of a particles transmitted (pass through) or
deflected through small angles
–  Tiny fraction deflected through large angles
Assist. Prof. Dr. İlkay KALAY The Modern View of Atomic Structure
of an atom The structure Nucleus Electron Neutron Proton Par.cle Charge Mass (amu) Electron NegaQve (-­‐1) 5.486 x 10-­‐4 Proton PosiQve (+1) 1.0073 Neutron Neutral (0) 1.0087 Par.cle Charge (C) Electron -­‐1.6022 x 10-­‐19 Proton 1.6022 x 10-­‐19 Neutron 0 26 Assist. Prof. Dr. İlkay KALAY The Modern View of Atomic Structure
of an atom The structure The atoms are small and the atomic dimensions are expressed in terms of Angstrom (Å) unit. 1 Å = 10-­‐10 m Nucleus ~ 10-­‐4 Å 1-­‐5 Å Schema.c view of an atom 27 Assist. Prof. Dr. İlkay KALAY The Modern View of Atomic Structure
of an atom The structure ü  All atoms of an element have the same number of protons in the nucleus. ü  The number of protons in the nucleus of an atom is called atomic number (Z). ü  Because the atoms have no net electrical charge, # of protons = # of electrons. ü  The total number of protons and neutrons in a nucleus is called mass number (A). Mass number = A Atomic number = Z 12
6
C
28 Today: Periodic Table of the Elements
40
Atomic number
91.224
Atomic symbol
Atomic weight
Zr
-­‐  Elements on the leq side and in the middle of the periodic table (except for hydrogen) are metallic elements or metals. -­‐  Nonmetals are separated from metals. -­‐  Metalloids exist between metals and nonmetals. 30
30 N. Bohr (1912)
•  Many phenomena involving
electrons in solids could not be
explained in terms of
CLASSICAL MECHANICS.
•  We need QUANTUM MECHANICS… Bohr Atom
orbital electrons:
n = principal
quantum number
1
2
n=3
Adapted from Fig. 2.1,
Callister 6e.
Nucleus: Z = # protons N = # neutrons Atomic mass A ≈ Z + N 2
Bohr’s Model
The lower the value of n, the smaller the radius of the orbit, and the lower the energy level. n=1 ground state (lowest energy state) (orbit closest to the nucleus) n=2, 3, or higher excited state The arrows refer to the transi?ons of the electron from one allowed energy state to another. Energy levels in the hydrogen atom from the Bohr model. 33 Electronic Structure
•  Electrons have wavelike and parQculate properQes. –  This means that electrons are in orbitals defined by a probability. –  Each orbital at discrete energy level determined by quantum numbers. Quantum # DesignaQon n = principal (energy level-­‐shell) K, L, M, N, O (1, 2, 3, etc.) l = subsidiary (orbitals) s, p, d, f (0, 1, 2, 3,…, n -­‐1) ml = magneQc 1, 3, 5, 7 (-­‐l to +l) ms = spin
½, -­‐½ 34 Electronic Energy States
Electrons... • have discrete energy states • tend to occupy lowest available energy state. 4d 4p N-­‐shell n = 4 3d 4s Energy 3p 3s M-­‐shell n = 3 Adapted from Fig. 2.4, Callister 7e. 2p 2s L-­‐shell n = 2 1s K-­‐shell n = 1 35 Electron Configurations
• Most elements: Electron configuraQon not stable. Atomic # Electron configuraQon Element Hydrogen 1 1s 1 Helium 2 1s 2 (stable) Lithium 3 1s 2 2s 1 Beryllium 4 1s 2 2s 2 Adapted from Table 2.2, Boron 5 1s 2 2s 2 2p 1 Callister 7e. Carbon 6 1s 2 2s 2 2p 2 ... ... Neon 10 1s 2 2s 2 2p 6 (stable) 1s 2 2s 2 2p 6 3s 1 Sodium 11 Magnesium 12 1s 2 2s 2 2p 6 3s 2 Aluminum 13 1s 2 2s 2 2p 6 3s 2 3p 1 ... ... Argon 18 1s 2 2s 2 2p 6 3s 2 3p 6 (stable) ... ... ... Krypton 36 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable) • Why? Valence (outer) shell usually not filled completely. 36 Why Study Atomic Structure and
Interatomic Bonding?
Two Allotropes of CARBON
Graphite
-  Relatively soft
-  Greasy feel to it
-  Reasonably good
conductor of electricity
Diamond
-  The hardest known material
-  Poor conductor of electricity
The dispari.es in proper.es are aSributed to a type of interatomic bonding found in graphite that does not exist in diamond Atomic Bonding
Essentially atoms either want to give up (transfer) or acquire (share) electrons
to complete electron configurations; minimize their energy
Transfer of electrons => ionic bond
Sharing of electrons => covalent
Metallic bond => sea of electrons
Magnesium oxide
Sulfur
Gold
Bromine
Sucrose
COVALENT BONDING Sharing of electrons between two atoms Magnesium
Copper
METALLIC BONDING Bonding of metal atoms to neighbor atoms Potassium dichromate
Nickel
(II) oxide
IONIC BONDING ElectrostaQc forces between ions Ionic Bonding
• Occurs between + and – ions (anion and caQon). • Requires electron transfer. • Large difference in electronegaQvity required. • Example: NaCl Na (metal) unstable Cl (nonmetal) unstable electron Na (caQon) stable + Coulombic ASracQon - Cl (anion) stable 39 Ionic bond – metal + nonmetal donates accepts electrons electrons Dissimilar electronegaQviQes ex: MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4 [Ne] 3s2 Mg2+ 1s2 2s2 2p6 O2-­‐ 1s2 2s2 2p6 [Ne] [Ne] 40 Covalent Bonding
•  Requires shared electrons
•  Example: CH4 C: has 4 valence e-­‐, needs 4 more CH4 H: has 1 valence e-­‐, needs 1 more H ElectronegaQviQes are comparable. H C H shared electrons from carbon atom H shared electrons from hydrogen atoms Adapted from Fig. 2.10, Callister 7e. 41 Metallic Bonding
• Arises from a sea of donated valence electrons
(1, 2, or 3 from each atom).
Non valence and atomic
nuclei form ion cores.
Ion cores in the sea of
electrons .
Valance electrons belong no
one particular atom but drift
throughout the entire metal.
Free electrons shield + ly
charged ions from repelling
Adapted from Fig. 2.11, Callister 6e.
each other…
• Primary bond for metals and their alloys
12
Secondary Bonding
Arises from interacQon between dipoles • FluctuaQng dipoles asymmetric electron clouds + -­‐ secondary bonding ex: liquid H H 2 + -­‐ H H 2 H 2 H H secondary bonding Adapted from Fig. 2.13, Callister 7e. • Permanent dipoles-­‐molecule induced -­‐general case: + -­‐ex: liquid HCl H -­‐ex: polymer -­‐ secon
Cl dary
secondary bonding + secondary bonding H bond
ing -­‐ Adapted from Fig. 2.14, Callister 7e. Cl secondary bonding 43 Summary: Bonding
Comments
Type
Bond Energy
Ionic
Large!
NondirecQonal (ceramics) Covalent
Variable
DirecQonal (semiconductors, ceramics polymer chains) large-­‐Diamond
small-­‐Bismuth
Metallic
Variable
large-­‐Tungsten
NondirecQonal (metals) small-­‐Mercury
Secondary
smallest
DirecQonal inter-­‐chain (polymer) inter-­‐molecular 44 Fundamentals of Materials Science: Processing,
Structure, Properties and Performance of Materials
Processing
single crystal polycrystal: low porosity polycrystal: high porosity Structure
Properties
Three disk specimens of aluminum oxide
Performance
45 Structure
Relates to the arrangement of its internal structure
2 0
n m
Cu
Plate-like
Cu Z
10 r
7
Zr
Plate-like
Macroscopic
Cu10Zr7
Microscopic
Atomic
Subatomic
Sources 1.  Textbook: CHEMISTRY: The Central Science, 9th ediQon, 2003 2.  Some of the images were taken from textbook, Wikipedia and Google. 3.  Materials Science and Engineering, W. FD. Callister, D. G. Rethwisch, 8th ediQon, 2011. 47