Principles of Materials Science and Engineering Introduction to Materials PDF

Principles of Materials Science and Engineering Introduction to Materials Marga San Juan Ateneo de Manila University As scientists, we study MATTER! Matter… Has mass Has volume (occupies space)...

Principles of Materials Science and Engineering Introduction to Materials Marga San Juan Ateneo de Manila University As scientists, we study MATTER! Matter… Has mass Has volume (occupies space) Images from: https://cdn.britannica.com/78/178878-138-E707FE4D/anything-spa ce-change-states-matter-substance-forms.jpg?w=400&h=225&c=c rop https://cdn.britannica.com/26/152026-050-41D137DE/Sunshine-le aves-beech-tree.jpg https://www.rubi.com/en/blog/wp-content/uploads/2023/02/header- v-small.jpg  States of matter State Solid Liquid Gas Particles Tightly bound together Close together but Widely separated and unordered move independently Shape Definite Not definite Not definite Volume Definite Takes shape of Uniformly fills its container container Compressibility Not appreciably Not appreciably Compressible Then, what are materials? Materials are an essential part of our everyday lives For our scope in this course, we will be focusing on solids Specifically, those that are being used or have a potential use for a particular engineering application And why are they important? “Materials are at the core of all technological advances.” - Schaffer, “The Science and Design of Engineering Materials”  Timeline of materials When Materials Science and Engineering as a discipline started (1955) Reference: doi: 10.1007/s42824-021-00044-0 https://www.tandfonline.com/doi/pdf/10.1080/09500830802047056 Stone age (up to 2.5 M years BCE) Stones, like flint and quartz are shaped for tools ○ Solid and useful due to its hardness, sharpness, and durability Would also use other materials, such as bone Images: https://www.thoughtco.com/thmb/-b2--at5qq7JlEWrhxKB80q2d6I=/1500x0/filte rs:no_upscale():max_bytes(150000):strip_icc()/france-stone-tools-including-scra per-burin-gimlet-and-bifacial-points-96506325-57a720fa3df78cf459e26849.jpg Bronze age (3500 BCE) Native copper had been in use since around 7000 BCE, but was only produced abundantly in kiln furnaces around 4000 - 3500 BCE ○ Malleable but had poor hardness Inclusion of tin made bronze, an alloy with greater hardness than pure copper Iron Age (1400 BCE) A method to reduce ferrous oxides to iron was developed ○ Stiffer, stronger, and harder than bronze Revolutionized agriculture and warfare Steel Age (mid 1800s - 1900s CE) Bessemer process in 1856 made industrial production of steel possible ○ Has a massive role in modern structural design to this day, together with concrete Polymer Age (mid-1900s) Began with the initial formulation of Bakelite in 1909 and synthetic rubber in 1922 ○ Majority of commercial polymers were developed between 1940 - 1960 Polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), etc. Silicon/Information Age (1950s - early 2000s) Development of transistor-grade silicon revolutionized electronics and modern computer science ○ The transistor has been said to have “the most far-reaching impact of any scientific or technological discovery to date” - Schaffer, 1995 And now? Nanomaterials Any questions? Principles of Materials Science and Engineering The Central Theme of MSE Marga San Juan Ateneo de Manila University  MSE TETRAHEDRON Now that we Processing & Synthesis know what materials are… Characterization what is Materials Science and Property Engineering all about? Performance Structure STRUCTURE Relates to the arrangement of the internal components of a material “Subatomic → Atomic → Microscopic → Macroscopic” To better understand the arrangement of components, you can watch this video: https://www.youtube.com/watch?v=0fKBhvDjuy0& Is it crystalline or amorphous? Is the structure cubic, tetragonal, or monoclinic? PROPERTY The technical/engineering definition for property is: ○ A material trait expressed in terms of the kind and magnitude of response to an imposed stimulus Generally independent of size and shape Determining the property of a material requires that something needs to be done to it by applying a stimulus, which will then give out a “response” PROCESSING & SYNTHESIS The method by which a material is manufactured ○ May also be called fabrication, or manufacturing technique Depending on the material type, a specific terminology may be more applicable PERFORMANCE The ability of a material to conform to its intended purpose ○ How well does the material live up to the specifications? ○ For a specific application, there are parameters that can be specified and quantified to assess how well the material “performs” CHARACTERIZATION The range of processes/techniques by which a material’s structure, properties, and performance can be probes and measured ○ Could also refer to Testing Techniques ○ This is how we interact with the material to bring out information about its structure, properties, or performance What’s the difference between Materials Science and Materials Engineering? What is Involves investigating the Materials relationships that exist between the Science? structure and properties of materials STRUCTURE ⇔ PROPERTY Scientific discipline which is primarily concerned with the search for basic knowledge about the internal structure, properties and processing of materials What is Materials Designing or engineering the structure of materials to produce a Engineering? predetermined set of properties Engineering discipline which is primarily concerned with the use of fundamental and applied knowledge of materials so that they can be converted into products needed or desired by society  “Involves investigating why materials behave the way that they do, as well as how materials are made and how they can be improved” It’s an interdisciplinary field Then, what is which combines chemistry, physics and engineering to study, Materials Science utilize, and improve on materials and Engineering? for the benefit of society and the environment  MSE TETRAHEDRON Processing & Synthesis So, back to Characterization this Property Performance Structure  MSE TETRAHEDRON Processing & Synthesis MSE is the inter-relationship Characterization of these five key Property concepts Performance Structure  Structure-property-processing-performance Disk specimens of aluminum oxide (Al2O3) All have identical compositions, but exhibit different degrees of transparency (property). Why? Any questions? Principles of Materials Science and Engineering Properties of Materials Marga San Juan Ateneo de Manila University  What will be the focus of the course? We will focus on the “Materials Science” aspect Specifically, the course will explore the structure - property relationship found in materials Source: https://www.researchgate.net/publication/353732537_Effect_of_using_nanotechnology_in_marine_industries_with_emphasis_on_typical_applications_in_Persian https://i.natgeofe.com/n/4e9c05b7-545c-4054-ab81-3be04e099a43/Gecko_foot.jpg https://www.acs.org/content/dam/acsorg/education/students/highschool/chemistryclubs/infographics/geckos-infographic.pdf MECHANICAL PROPERTY Relates deformation (response) to an applied load or force (stimulus) Is the material hard or soft? Strong or weak? Examples of quantifiable mechanical properties: modulus of elasticity, yield strength MECHANICAL PROPERTY What mechanical properties would you want to have for an automobile windshield? MECHANICAL PROPERTY Mechanical properties are very important considerations in the selection of a material even if the mechanical property is not the main property of concern ○ All real materials have mass, which means that its own weight (stimulus) acts on itself, and thus may play a significant role in its mechanical behavior ELECTRICAL PROPERTY Response to an electric field Will electrical charges flow in the material as a response to the field? Is it a conductor, insulator or semiconductor? Examples of quantifiable electrical properties: electrical conductivity, dielectric constant ELECTRICAL PROPERTY What electrical properties (qualitative descriptions are okay) would you want to have for your computer processor? THERMAL PROPERTY response to heat energy Will it allow heat to flow? Is it a (thermal) conductor or insulator? Examples of quantifiable thermal properties: thermal conductivity conductivity, heat capacity THERMAL PROPERTY How is it possible that coffee remains hot for extended periods of time in your thermos bottle? MAGNETIC PROPERTY response to a magnetic field Will it be attracted to a magnet or not? Can it be magnetized? Example of a quantifiable magnetic property: susceptibility MAGNETIC PROPERTY Are magnetic properties important in earphones or airpods: OPTICAL PROPERTY response to electromagnetic radiation (ex. light) Is it transparent, translucent or opaque? What is its color? Example of a quantifiable optical property: index of refraction OPTICAL PROPERTY Can we make transparent windows that also generate electricity? DETERIORATIVE PROPERTY Indicates the chemical reactivity of materials Response to a corrosive/reactive environment ○ What will be the extent of corrosion after a certain period of time in a certain environment ○ These properties are highly chemistry-dependent and we normally don’t specify deteriorative properties the same way as the previous properties. DETERIORATIVE PROPERTY Can we prevent metals from corroding?  The Materials Selection Process Determine required properties 1. Pick Application Properties: mechanical, electrical, thermal, magnetic, optical, deteriorative Identify candidate Material(s) 2. Properties Material: Structure, Composition Identify required Processing 3. Material Processing: Changes structure and overall shape ex: casting, sintering, vapor deposition, doping, forming, joining, annealing. Any questions? Principles of Materials Science and Engineering Major Classification of Materials Marga San Juan Ateneo de Manila University  METALS Metals comprise almost 80% of all elements! METALS Aside from being single elements, they can be “mixed” to form what we call a METAL ALLOY or simply an ALLOY Examples: Steel (Iron and Carbon) *We can combine non-metallic elements to metallic elements and still Bronze get an alloy (Copper and Tin)  METALS Aluminum (Cubic) Steel microstructure http://www.phase-trans.msm.cam.ac.uk/2008/Steel_Microstructure/SM.html METALS General Mechanical Characteristics Strong: Takes some effort (force) to deform Ductile: Can be formed into thin wires without breaking Malleable: Can be formed into thin sheets without breaking METALS Other characteristics Good electrical conductors: Used as wires Good thermal conductors: Used as heat sinks – for dissipating heat energy Characteristic metallic luster: Surfaces are highly reflective Very opaque  CERAMICS Chemical compounds between metallic and non-metallic elements; can also be compounds between non-metallic elemental solids and non-metals Non-metallic elemental solids (NMES) Non-metallic elements which are solids under ordinary conditions  CERAMICS They frequently occur as nitrides (contains nitrogen), oxides (contains oxygen), or carbide (contains carbon) Silica (SiO2) Pottery Abrasive paper Main constituent of Mixture of different (Sandpaper) sand and typical glass oxides of silicon and Has silicon carbide windows/panels aluminum (SiC) Salt Sodium chloride (NaCl)  CERAMICS Silicon Carbide (SiC) Perovskite (SrTiO3) https://www.perovskite-info.com/introduction#:~:text=Perovskite%20is%20a%20calcium%20titanium,Perovski%20(1792%E2%8 0%931856). CERAMICS Mechanical Characteristics Stiff and Strong: takes some effort (force) to deform or change its shape Brittle: easily breaks CERAMICS Other Characteristics Poor electrical conductors (insulators) Poor thermal conductors Can be transparent or opaque  POLYMERS Consist of long organic molecular chains Many of them are organic compounds that are chemically based on carbon, hydrogen, and other nonmetallic elements (e.g. O, N, and Si) Most chemically complex in terms of composition A bit “controversial” due to environmental concerns E.g. Plastics, rubbers, adhesives, flims, fibers  POLYMERS Polyethylene Polyvinyl chloride Polyethylene terephthalate (PET) Styrene - Butadiene Polyurethane  POLYMERS Polyaniline Rubber (polyisoprene) https://www.pslc.ws/macrog/exp/rubber/sepisode/pi/pi.htm POLYMERS Mechanical Characteristics Soft and weak: Very easy to deform Ductile Low density POLYMERS Other Characteristics Poor electrical conductors (insulators) Poor thermal conductors Low softening temperatures Can be transparent, translucent or opaque  SEMICONDUCTORS A unique class due mainly to their electrical behavior Have electrical properties intermediate between conductors and insulators The uniqueness is because of the fact that electrical properties (electrical conductivity) are extremely sensitive to minute concentrations of impurity atoms ○ Adding 1 atom of an impurity in 1012 atoms of the host semiconductor could significantly change the conductivity  SEMICONDUCTORS This class of materials made possible the advent of integrated circuitry that has totally revolutionized the electronics and computer industries over the past four decades → led to the so-called “digital/information age”  SEMICONDUCTORS Silicon Gallium Arsenide Most dominant “elemental” semiconductor Is a “compound” semiconductor; widely → can find a silicon “integrated chip” in used for high-efficiency solar cells and laser practically any electronic device diodes The GaAs chunk also has a characteristic metallic luster This raw silicon looks like a rock, but has By MidSTAR.jpg: United States Naval a metallic luster. It is brittle and will Academyderivativework: Materialscientist(talk) -MidSTAR.jpg, Public Domain, shatter if too much force is applied. https://commons.wikimedia.org/w/index.php?cu rid=17403944  COMPOSITES Consist of two or more materials from within the same class or among different material classes ○ Combination of different materials to arrive at a new, “hybrid” material class Design goal: Is to achieve a combination of properties that is not displayed by any single material, and also to incorporate the best characteristics of each of the the component materials Properties that can be obtained vary widely Sample combinations: metal-metal, polymer-polymer, metal-ceramic, polymer-ceramic, etc.  COMPOSITES Concrete Fiberglass A mixture of various Fine glass fibers ceramic materials: embedded in a cement, sand, gravel, polymer matrix stone Plywood Composed of several layers of wood COMPOSITES Modern aircrafts are made up of various types of composite materials  MODIFIED MSE TETRAHEDRON Metals We can adapt the MSE tetrahedron Composites for the major classifications of Ceramics materials Semiconductors Polymers Room-temperature density comparison Metals are usually the densest materials Room-temperature elastic modulus (stiffness comparison) Polymers are usually the least stiff (easiest to deform) materials Room-temperature tensile strength comparison Polymers are usually the weakest materials Room-temperature resistance to fracture comparison Ceramics and polymers usually fracture easily Room-temperature electrical conductivity comparison Metals are conductors, ceramic, and polymers are insulators Any questions? Principles of Materials Science and Engineering Advanced Materials Marga San Juan Ateneo de Manila University ADVANCED MATERIALS “Advanced” or “High-tech” materials are considered to be the “Materials of the Future” It’s a miscellaneous classification because they can be categorized to any of the general types previously presented Advanced Materials Need to have adequate properties for use in applications that are relatively more intricate or sophisticated ○ Traditional materials with enhanced properties ○ Newly developed, high performance materials  BIOMATERIALS Employed in components implanted into the human body for replacement of diseased or damaged body parts Must not produce toxic substances and must be compatible with body tissues (i.e., must not cause adverse biological reactions) You can learn more from this video: https://www.youtube.com/watch?v= uta5Vo86XL4  SMART MATERIALS/SYSTEMS Able to sense changes in their environments and then respond to these changes in predetermined manners Components of a smart material (or system) include some type of sensor (that detects an input signal), and an actuator (that performs a responsive and adaptive function) Piezoelectric Shape memory alloys material Return to a Electrical stimulus to pre-determined shape mechanical actions with an increase in Used in ink-jet printer temperature https://youtu.be/TSG https://youtu.be/2lv6 fitxlkzI Vs12jLc  SMART MATERIALS/SYSTEMS Common types of actuators Shape-memory alloys: After initial deformation, will revert to their original shape with a change of temperature Piezoelectric ceramics: Expand and contract in response to an electric field and vice versa Magnetostrictive materials: Analogous to piezoelectric materials but in response to a magnetic fields Electrorheological/Magnetorheological fluids: Viscosity changes in response to electric/magnetic fields  NANOMATERIALS Can be from any of the 4 basic material types Have one or more dimensions in the order of 1 –100 nanometers (nm) [1 nm = 1 x 10-9m] At the nano level, new phenomena can be observed which are not seen in larger scales Graphene Nanofibers Nanoparticles Nanoparticles Fullerene Nanotube Graphite Various forms of carbon in the You can find out more here: https://youtu.be/IkYimZBzguw nanoscale  OTHER MATERIALS OF INTEREST https://www.youtube.com/watch?v=ODZgSAeLlEQ& https://www.youtube.com/watch?v=az6oYcd-SfU& Any questions? Principles of Materials Science and Engineering Atomic Structure and Definitions Marga San Juan Ateneo de Manila University  Review: What is “structure”? The arrangement of internal component of the material To study the internal components of a material, we need to go back to our general chemistry concepts ATOMS AND MOLECULES Matter - and materials - is composed of “atoms” and “molecules” Atoms The smallest unit of matter that cannot be made any smaller without losing its identity without losing its identity From the Greek word “atomos” meaning “indivisible” Atoms have different “identities” – these are what we call the “ELEMENTS” ATOMS AND MOLECULES Matter - and materials - is composed of “atoms” and “molecules” Elements These are the building blocks of all matter and materials There is only a limited number as what you can see in the “periodic table” ATOMS AND MOLECULES Molecule Group of atoms held together so that they form a unit whose identity is distinguishably different from the atoms alone They are held together by forces which we call “chemical bonds” The groups of atoms can be identical or different from one another. If they are different, we call the group a “COMPOUND”  ATOMIC STRUCTURE Matter is composed of atoms Atoms have a nucleus which contains protons and neutrons The nucleus is a very small fraction of the volume of an atom *Solar system depiction of atomic structure. ○ Emphasizes proton, neutron and electron distribution; but does not accurately depict current accepted model of atomic structure. ATOMIC STRUCTURE Electron cloud model The nucleus is surrounded by a “cloud or sea” of electrons ○ Electrons have a certain probability of being found around the nucleus → Do not have definite orbits ○ Orbitals are regions around the nucleus with a high probability of finding electrons Atomic Structure Protons ○ Particles with a positive charge (1.60 x 10-19 C) ○ Mass of one proton = 1.673 x 10-24 g Electrons ○ Particles with a negative charge (-1.60 x 10-19 C) ○ Mass of one electron = 9.11 x 10-28 g Neutrons ○ Electrically neutral particles (no charge) ○ Mass of one neutron = 1.675 x 10-24 g (no charge) Atomic Number, Z The number of protons in the nucleus ○ For an electrically neutral/complete atom, Z = # of protons = # of electrons. This is what distinguishes one element from another; it defines its identity ○ E.g. Copper (Cu) has an atomic number of 29 → No other element has an atomic number of 29 Atomic Mass Number or Mass Number, A Total number of protons and neutrons in an atom ○ Why are electrons not included in the mass number? Atomic Mass, m Mass of an atom = sum of the masses of all the protons and neutrons in an atom ○ Because of the very small masses, we can introduce another unit for these very small scales Atomic Mass Unit (amu) or Dalton (Da or u) ○ 1 amu = 1 Da = 1.6605 x 10-23 g Atomic Mass, m 1 amu is defined as 1/12 of the atomic mass of carbon 12 (12C) which is the most common isotope for the element ○ Mass 12C: A = 12.00000 Atomic Mass, m Isotopes ○ Are atoms of an element that differ in the number of neutrons in their nucleus Same Z but different A → Results in different mass numbers ○ E.g Carbon has two stable isotopes Atomic Weight (Relative Atomic Mass) Weighted average of the atomic masses of an atom’s naturally occurring isotope E.g. Carbon ○ Carbon-12 = 12.0000 x 0.9893 = 11.871 amu ○ Carbon-13 = 13.0036 x 0.0107 = 0.1391 amu ○ Therefore, atomic weight = 11.871 + 0.139 12.01 amu per atom C Molecular weight ○ Sum of atomic weights of all atoms in a molecule  OTHER RELEVANT INFORMATION The atomic weight can also be expressed in another unit ○ Grams per mole (g/mol) Mole: Quantity of a substance corresponding to 6.022 x 1023 (Avogadro’s number) atoms/molecules/ions Thus, in the previous example, the atomic weight of C can be expressed as 12.01 g/mol of C atoms or 12.01 g per 6.022 x 1023 C atoms SYMBOLIC REPRESENTATION Any questions? Principles of Materials Science and Engineering Atomic Models Marga San Juan Ateneo de Manila University  Bohr Atomic Model Electrons are assumed to revolve around the atomic nucleus in discrete orbits The position of any electron is well defined in terms of orbits The energies of electrons are quantized ○ Discrete values  Bohr Atomic Model Changing the energy of electron occurs via a quantum jump ○ Absorption of energy to a higher orbit ○ Emission of energy to a lower orbit Describes electrons in terms of: ○ Position: Electron orbits ○ Energy: Quantized energy levels Energy levels are separated by finite energy  Quantum-mechanical Model Quantum mechanical model or Wave-Mechanical model replaced the Bohr model of the atom The quantum-mechanical model depicts electrons as both particles and waves spread through a region of space (delocalized) called an orbital. The consequence is that electrons are no longer moving in fixed orbits but the motion is described by a wave function/equation → Schrödinger equation The energy of the orbitals is quantized like the Bohr model  Quantum-mechanical Model Comparing the a) Bohr Wave-mechanical model and b) Wave-mechanical The position of an atom models in terms of electron is described electron distribution by a probability distribution Bohr model 100% certain that the electron is a particular distance from the nucleus  Quantum-mechanical Model Each solution of the wave function defines an orbital ○ Each solution is labeled by a letter and number combination: 1s, 2s, 2p, 3s, 3p, 3d, etc. ○ An orbital in quantum mechanical terms is actually a region of space rather than a particular point Shaded areas are where electrons are likely to be found rather than distinct orbits Quantum Numbers Solutions to the functions used to solve the wave equation ○ Quantum numbers are used to name atomic orbitals When solving the Schrödinger equation, three quantum numbers are used ○ Principal quantum number, n (n = 1, 2, 3, 4, 5, …) ○ Secondary or orbital quantum number, l ○ Magnetic quantum number, ml Quantum Numbers Characterizes the electron probability density ○ Size ○ Shape ○ Spatial orientation Quantum Numbers Principal Quantum Number, n n = 1, 2, 3, 4…positive integer ( the lower the value of n, the more stable is the state) Defines the shell in which a particular orbital is found ○ n= 1 is the first shell, n= 2 is the second shell, etc. each shell has different energy levels The only quantum number associated with the Bohr model (analogous to the size of the orbit) Related to the distance of an electron from the nucleus (size of orbit/shell) Quantum Numbers Secondary or Orbital Quantum Number, l The secondary quantum number, l, indexes energy differences between orbitals in the same shell in an atom ⇒ within the main shell, there are subshells l has integer values from 0 to n - 1 ○ L specifies the subshell ○ Each shell contains as many values as its value of n Quantum Numbers Secondary or Orbital Quantum Number, l Associated with the angular momentum of the revolving electron the letters s, p, d, f, g and have also been used to signify l = 0, 1, 2, 3, 4, 5 respectively ○ Thus, the energy level corresponding to n= 1 and l= 0 is called the 1s level, that for n= 2 and l=1 is called the 2p level etc.  QUANTUM NUMBERS The energies of orbitals are specified completely using only the n and l quantum numbers In magnetic fields, some emission lines (when electron jump to lower orbits) split into three, five, or seven components A third quantum number describes splitting Quantum Numbers Magnetic Quantum Number, ml Determines the number of “energy states” for each subshell Related to the component of the angular momentum in a specified direction Ml has integer values from -l to +l ○ ml may be either positive or negative ○ Ml’s absolute value must be less than or equal to l ○ E.g. l = 1, ml = -1, 0, +1 l = 3, ml = -3, -2, -1, 0, +1, +2, +3 QUANTUM NUMBERS  QUANTUM NUMBERS: ACTIVITY Write all of the allowed sets of quantum numbers (n, l, and ml) for a 3p orbital. Solution: The 3p designation tells us the values of n and l ○ n = 3 while l = p = 1 Thus, permissible values for ml will range from -l to +l ○ l = -1, 0, +1 Therefore, the allowed sets for the 3p orbital are  ORBITALS An orbital is the region of space where we can find the electron ⇒ this region of space has different shapes Quantum Numbers Spin Quantum Number, ms Related to the spin of the electron about its own axis ○ Recall: Electrons are revolving around the nucleus; as they revolve, they also rotate (spin) similar to the planetary model Can only have a value of ½ (only two possible values) Determines the number of electrons that can occupy an orbital  Electron “condominium” analogy The quantum numbers essentially tell us the “address” or probable location of an electron What Floor? What Floor? ○ 1st, 2nd, etc. ○ n = 1, 2, etc. What Wing? What Wing? ○ North, east, etc. ○ l = 0, 1, … n - 1 What room? What room? ○ 301, 302, etc. ○ ml = -1, …0…, +1 Which bed? Which bed? ○ Bed 1 or Bed 2 (only 2) ○ ms = +½ or -½  QUANTUM NUMBERS The table summarizes how many electrons the can be seen in each shell and subshell  QUANTUM NUMBERS Alphanumeric designation for the atomic orbitals Energies of orbitals Schematic representation of the relative energies of the various shells and subshells. The smaller the n, the lower the energy level Within each shell subshell energy increases with l Overlap of energy levels within one shell is possible with states in an adjacent shell Energies of orbitals Thinking of the electron condominium Here, we see the individual “rooms”, orbitals or “states” We can see that there are orbitals which have identical energy levels –we term this as “degenerate” orbitals  PRINCIPLES FOR DETERMINING ROOMS/STATES Pauli Exclusion Principle Each electron state can hold no more than 2 electrons, which must have opposite spins Aufbau principle When filling orbitals, start with the lowest energy and proceed to the next highest energy level  PRINCIPLES FOR DETERMINING ROOMS/STATES Hund’s rule Within a subshell, electrons occupy the maximum number of orbitals possible ○ The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins E.g. Sodium Atom The atomic number of sodium is 11. We assume that it is neutral, so there should be 11 electrons. The sequence of filling up, following the previous principles, is thus ○ First 2 electrons of opposite spins fill up the 1s orbital ○ Next 6 electrons: 2p orbital Fill up each 2p orbital with 1 electron each of identical spin, Then, pair it up with electrons of opposite spin ○ Last 1 electron: 3s orbital E.g. Sodium Atom (alternative diagram) Electrons are represented by arrow up or arrow down (two spins) The sequence of filling up, following the previous principles, is thus: ○ First 2 electrons of opposite spins fill up the 1s orbital ○ Next 2 electrons: 2s orbital ○ Next 6 electrons: 2p orbital Fill up each 2p orbital with 1 electron each of identical spin (blue first) then, pair it up with electrons of opposite spin (red) ○ Last 1 electron: 3s orbital  ELECTRON CONFIGURATION Can further simplify the pictorial representation Electron configuration describes how the electrons are distributed among the various atomic orbitals in an atom  ELECTRON CONFIGURATION Recall the sequence for filling up the electron configuration corresponds to the sequence of energies E.g. Sodium Atom (alternative diagram) For the sodium atom, follow the sequence of filling up: ○ 1s is completely filled ⇒ 1s2 ○ 2s is completely filled ⇒ 2s2 ○ 2p is completely filled ⇒ 2p6 Accounting for the three 2p degenerate orbitals ○ 3s is partially filled ⇒ 3s1 Electron config. of Na: 1s22s22p63s1 ○ Superscripts add up to total no. of electrons Electron configuration is a convenient way of identifying how electrons are arranged around the nucleus, i.e. an atom’s structure Terminologies Ground state ○ When electrons occupy the lowest possible energies Valence electrons ○ Electrons that occupy the outermost shell The valence electrons will be of primary concern as these are the ones that participate in the bonding between atoms They determine many of the physical chemical properties of materials  SURVEY OF ELEMENTS Most elements: Electron configuration is not stable Most elements: Electron configuration is not stable Why? ○ Valence (outer) shell is usually not filled completely Elements which are not stable have greater tendencies to react or bond with other elements. Ions It is possible for an atom to lose or gain electrons Ions are formed when the number of protons and electrons in an atom are not equal ○ Ions with more protons than electrons are called cations Net positive charge (e.g. Sodium ion - Na+) ○ Ions with more electrons that protons are called anions Net negative charge (e.g. Chloride ion - Cl-) The Periodic Table Was introduced by D. Mendeleev, a Russian scientist, in 1869 ○ Elements are situated with increasing atomic number, in seven horizontal rows called periods ○ Elements of any given family which show a similarity in chemical properties are arranged in the same column or group PERIODIC TABLE  PERIODIC TABLE Electropositive elements: Readily give Electronegative elements: Readily up electrons to become + ions acquire electrons to become - ions *Numbers in red are electronegativity values Any questions? Principles of Materials Science and Engineering Atomic Bonding Marga San Juan Ateneo de Manila University Interatomic bonding Consider, two identical atoms of the same element represented as spheres Each atom has positive protons in the nucleus surrounded by negative electrons Interatomic bonding At large distances (r), the atoms do not sense each other. ○ There is no interaction between them: Interatomic bonding But as the distance, but as the distance, r between them decreases: ○ The positive nucleus of one atom, senses the negative electrons of the other atom, and vice versa. ○ Because the charges are different, there will be an attractive force developed between the two atoms. Interatomic bonding As the distance becomes even closer: ○ The positive nucleus of one atom, senses the positive nucleus of the other atom, and vice versa. The electrons of one atom, senses the electrons of the other. ○ Because the interaction is now between like charges, there will be an additional repulsive force developed between the two atoms.  INTERATOMIC BONDING The “bonding forces” can be plotted as a function of distance or interatomic separation, r  INTERATOMIC BONDING At every distance r, we can add the attractive and repulsive forces to get a net force vs. r curve  INTERATOMIC BONDING As atoms are brought closer together, there is a net attractive force Attractive forces increase, reach a maximum, then start to decrease  INTERATOMIC BONDING At much closer distances, the net force becomes repulsive  INTERATOMIC BONDING There is a certain distance ro, where the net force is zero ro: “Equilibrium distance/spacing” (~0.3 nm)  INTERATOMIC BONDING At ro, the atoms can be said to be “chemically bonded” to one another ro: “Equilibrium distance/spacing” (~0.3 nm) Interatomic bonding From the force vs. distance curve, any attempt to separate atoms which are chemically bonded will result in a net force: ○ If we try to separate them (increase r), an attractive force will be developed to bring them back to ro ○ If we try to push them to each other (decrease r), a repulsive force will develop to restore them to ro ○ We can now imagine two atoms at ro to be held together by a relaxed spring If you stretch or compress, the tendency is to go back to the relaxed state at ro  Potential Well Concept The force vs. distance curve can be converted to a potential energy, E vs. distance curve by integration: For our atomic system which has attractive and repulsive components: Like in the case of forces, the energies can also be plotted as a function of distance, r shown in the next slide. It somehow looks like an inverted force vs. distance curve. But note differences carefully.  Potential Well Concept As the distance decreases, the net potential energy decreases, reaches a minimum, then again increases  Potential Well Concept At ro, the potential energy of the system is lowest (minimum) When atoms are bonded together, the energy is at the bottom of the “potential well” Any attempt to change the distance between the atoms requires an increase in energy Bonding Energy Energy at ro Corresponds to the “depth” of the well Represents the energy that would be required to separate two atoms that are chemically bonded ○ Solid: Large bonding energies (Eo) with deep wells Melting temperature and cohesive properties reflect the magnitude of the bonding energy ○ Gas: Low bonding energies ○ Liquid: Intermediate bonding energies  Types of Bonding PRIMARY BONDING SECONDARY BONDING Chemical in nature Also known as Arises from the tendency of Intermolecular forces of the atoms to assume stable attraction electron structures by Physical in nature and are completely filling the generally weaker than the outermost shell primary ones E.g. Ionic, covalent, and E.g. Van de Waals, hydrogen metallic bonding bonding Ionic bonding Found in compounds that are composed of both metallic and nonmetallic elements Develops when electron/s are transferred from atoms of active metallic elements to atoms of active non metallic elements, thereby enabling each of the resultant ions to attain a stable closed shell Bond is non directional (magnitude of the bond is equal in all direction around the ion) Relatively have large bonding energies Ex. sodium chloride (NaCl) Ionic bonding Attractive bonding forces are coulombic ○ Attraction is due to interaction between unlike charges Attractive and repulsive energies for two isolated atoms are given by: A, B, and n are constants where n~8 Can you think of any material type/s that is/are ionically bonded? Ionic bonding In ionic solids, the ions are arranged in a crystal lattice* ○ Ions experience attractive and repulsive interactions in three dimensions. ○ Strength of interaction decreases with distance. *imaginary array of lines in three dimensions  Ionic Bonding In a solid lattice, any given ion experiences a large number of attractive and repulsive interactions. Ionic bonding The lattice energy is the overall result of the attractive and repulsive forces a crystal contains. ○ Small ions with large charges form ionic compounds with large lattice energies. ○ Large ions with small charges form ionic compounds with small lattice energies. Ionic Bonding in NaCl Covalent bonding Involves sharing of valence electrons to obtain a stable (inert) gas configuration Bonds are strongly directional *Directional → Between specific atoms and may exist only in the direction between one atom and another that participates in the electron sharing Ex. CH4 (molecule containing dissimilar atoms), H2 & Cl2 (non metallic elemental molecules), carbon & silicon (elemental solids) Covalent Bonding in CH4 Covalent bonding # of covalent bonds is determined by the # of valence electrons N’: 8 – N’ * It is possible to have bonds that are partially ionic and partially covalent: where XA and XB are the electronegativities of the respective elements What material type/s is/are covalently bonded? Valence Bond Model All chemical bonds are the result of overlap between atomic orbitals. For H2 , each H atom has a single valence electron in a 1s orbital. ○ The 1 s orbitals overlap to form the covalent bond. ○ s orbitals are spherical, there is no preferred direction of approach.  Ionic Bonding in NaCl Overlap of the 1s orbitals for the covalent bond in molecular hydrogen. ○ Top: Overlap shown by plotting the wave functions for the 1s orbitals. ○ Bottom: Shading to represent the buildup of electron density. Orbital Overlap and Chemical Bonding For N2 , the Lewis structure shows a total of 6 electrons shared: Each N atom has a single valence electron in each 2p orbital (1s2 2s2 2p3) The 2 p orbital set can overlap in different orientations due to their shapes.  Orbital Overlap: SIGMA (σ) Bond A 2 p orbital on one N overlaps end to end with a 2p orbital on the second N forming a sigma (σ) bond. A sigma bond is the result of constructive interference for end to end overlap, where electron density lies along a line between the bonding atoms.  Orbital Overlap: PI (π) Bond The remaining two 2 p orbitals on each N overlap side to side forming pi (π) bonds. ○ A pi bond is the result of constructive interference for side to side overlap , where electron density lies above and below, or in front and in back of a line between the bonding atoms. ○ Two pi bonds can form between the two nuclei. Hybrid Orbitals Orbital Hybridization reconciles the notion of orbital overlap with observations of molecular shapes and structures ○ Bond angle predicted by orbital overlap of p and s orbitals in H2O is 90o ○ Bond angle in H2O actually larger than 90o Hybrid Orbitals During orbital hybridization the repulsion between electrons in bonding atoms can be strong enough to reshape the orbitals of the atoms. ○ The angles between the reshaped orbitals must match observed bond angles. CH4 is the simplest binary compound of C and H ○ All four bond angles are 109.5o ○ Four identical orbitals with angles of 109.5o between them are needed on C Hybrid Orbitals Hybrid orbitals are created by a linear combination of atomic orbitals, producing an equal number of hybrid orbitals ○ Orbitals are mathematical in nature. ○ Two atomic orbitals combine, two hybrid orbitals are generated. Covalent bonding: Bond Hybridization Carbon can form sp3 hybrid orbitals  Covalent bonding: Bond Hybridization E.g. CH4 ○ C: 4 valence e-, needs 4 more ○ H: 1 valence e-, needs 1 more Electronegativities of C and H are comparable so electrons are shared in covalent bonds. Image from: https://img.brainkart.com/imagebk37/d72P6h7.jpg Metallic bonding Occurs in elements with only a few electrons in their outermost orbital (electropositive) Valence electrons are given up by individual atoms, resulting to a geometric array of positive ions surrounded by a free electron cloud (“electron gas”) Non-directional, which allows plastic deformation Ex. Sodium, Fe, alloys What material type/s is/are metallically bonded?  Schematic of metallic bonding The valence electrons are delocalized and move freely throughout the solid. This explain malleability, ductility and conductivity properties of metals  Metallic Bonding and Deformation When a force is applied to a metal, the positively charged cores respond to the stress, deforming the metal. The free flow of electrons maintains the bonding throughout the process. Van der Waals/Secondary bonding Exists between virtually all atoms or molecules Arise from atomic or molecular dipoles* *exists whenever there is some separation of positive and negative portions of an atom or molecule Schematic illustration of van der Waals bonding  Fluctuating induced atomic dipole bonds Temporary or induced dipoles are formed in neutral atoms when there is an instantaneous displacement of the positive nucleus relative to the negative electron cloud. Polar molecule-induced dipole bonds POLAR MOLECULES Permanent dipole moments exist in some molecules b virtue of an asymmetrical arrangement of positively and negatively charged regions Schematic representation of a polar hydrogen chloride (HCl) molecule Bond Polarity Electron density is not shared equally when elements with different electronegativities bond. ○ More than half of the electron density is associated with the more electronegative element ○ The more electronegative element experiences an increase in electron density and attains a partial negative charge ○ The less electronegative element experiences a decrease in electron density and attains a partial positive charge ○ The two points of positive and negative charge constitute a dipole. ○ The bond has an electric field associated with it.  Bond Polarity The formation of the polar covalent HF bond. ○ The more electronegative F has a partial negative charge. ○ The less electronegative H has a partial positive charge.  Metallic Bonding and Deformation Bond polarity is important in biocompatibility ○ Cells often have polar bonds on their surfaces that interact with water. ○ Substances such as amorphous silica can interact strongly with cell surfaces, such as the red blood cell, and damage them.  Hydrogen Bonding in HF Strongest secondary bonding type Occurs between molecules in which hydrogen is covalently bonded to fluorine , oxygen and nitrogen  Hydrogen bonding and volume expansion of water during freezing Water expands when it becomes solid because the strong hydrogen bonding forces molecules to orient in a specific way. This leaves more spaces in between molecules. Thus, making ice less dense than water. Any questions?