Joy of Science Discovering the matters and the laws of the universe

Transcription

1 January 16, 2017 Joy of Science Discovering the matters and the laws of the universe Key Words Universe, Energy, Quantum mechanics, Chemical reaction, Structure of matter Unless otherwise noted, all pictures are taken from wikipedia.org

2 Quiz 1 n Table salt (NaCl) forms a crystal in which the elements are held together by 1. covalent bonds 2. ionic bonds 3. metallic bonds 4. hydrogen bonds

3 Quiz 1 n Table salt (NaCl) forms a crystal in which the elements are held together by 1. covalent bonds 2. ionic bonds 3. metallic bonds 4. hydrogen bonds

4 Quiz 2 n One atom permanently receives an electron from another atom during the formation of 1. a covalent bond 2. an ionic bond 3. a metallic bond 4. a hydrogen bond

5 Quiz 2 n One atom permanently receives an electron from another atom during the formation of 1. a covalent bond 2. an ionic bond 3. a metallic bond 4. a hydrogen bond

6 Quiz 3 n What type of bond is formed when two hydrogen atoms share a pair of electrons to form a hydrogen molecule? 1. a covalent bond 2. an ionic bond 3. a metallic bond 4. a hydrogen bond

7 Quiz 3 n What type of bond is formed when two hydrogen atoms share a pair of electrons to form a hydrogen molecule? 1. a covalent bond 2. an ionic bond 3. a metallic bond 4. a hydrogen bond

8 Quiz 4 n If a sodium atom loses an electron to a chlorine atom, the resulting sodium ion 1. remains electrically neutral 2. acquires one unit of negative charge 3. acquires one unit of positive charge 4. acquires two units of positive charge

9 Quiz 4 n If a sodium atom loses an electron to a chlorine atom, the resulting sodium ion 1. remains electrically neutral 2. acquires one unit of negative charge 3. acquires one unit of positive charge 4. acquires two units of positive charge

10 January 16, 2017 Modern materials How have computers gotten so much faster? Today s Keywords Strength, composite materials, electrical conductor, resistance, insulator, semiconductor, superconductivity, doping, microchip

11 Contents n Introduction: materials and modern world n Three different properties of materials 1. Strengths of materials 2. Electrical properties of materials 3. Magnetic properties of materials

12 Introduction: materials and the modern world 1 n Look around your room now. How many different materials do you see? n Glass, wood, metal, woven fabric, n Thanks to the discoveries of chemists, the number of everyday materials has increased by a thousandfold in the past two centuries!

13 Introduction: materials and the modern world 2 n Chemists take natural elements and compounds of earth, air, and water, and devise thousands of useful materials. n Materials display many different properties: color, smell, hardness, luster, flexibility, density, texture, melting point, strength, and so on.

14 Introduction: materials and the modern world 2 n Chemists take natural elements and compounds of earth, air, and water, and devise thousands of useful materials. n Materials display many different properties: color, smell, hardness, luster, flexibility, density, texture, melting point, strength, and so on.

15 Introduction: materials and the modern world 3 n Three essential features of properties of each material (next page) n Based on the properties of atoms and their chemical bonding: 1. the of which it is made; 2. the way those ; and 3. the way the to each other.

16 Three different properties of materials Every material is held together by the bonds between its atoms. à Related to their atomic architecture. 1. The strength of materials 2. The ability of materials to conduct electricity 3. The magnetic property of materials

17 1.Strengths of materials Think about a plastic bag carrying a heavy load of groceries. How can something as light, flexible, and inexpensive as a piece of plastic be so strong?

18 Strength: n The ability of a solid to resist changes in shape. n A strong materials must be made with strong chemical bonds! n There is no type of bond universally stronger than others, but the strongest materials incorporate long chains and clusters of carbon atoms bonded by covalent bonds - Diamond, plastic shopping bags, spider webs are bonded by covalent bonds

19 Strengths of materials n The strength of a material is related to the size of the force it can withstand when it is pushed or pulled. n There are three very different kinds of strength characterizing materials: 1. its ability to withstand crushing (compressive strength); 2. its ability to withstand pulling apart (tensile strength); 3. its ability to withstand twisting (shear strength).

20 Strengths of materials (cont d) n Elastic limit: the point at which a material stops resisting external forces and begins to bend, break, or tear Ex) Breaking an egg, crush an aluminum can, or fold a piece of paper

21 Strengths of materials Let us think about what determines a material s strength!

22 Strengths of materials n Examples of materials with different strengths Diamond: strong under all three kinds of stress (left picture) Plastic shopping bag: strong under stretching, but weak under twisting or crushing strong (right picture)

23 Strengths of materials n Examples of materials with different strengths Diamond: strong under all three kinds of stress because of its 3-dimensional framework of strong carbon-carbon bonds (left picture) Plastic shopping bag: strong under stretching, but weak under twisting or crushing strong because of strong bonds in only one direction (right picture)

24 Strengths of materials What determines a material s strength? è A material s strength is a result of the <type> and <arrangements> of chemical bonds.

25 Composite materials: n Combined materials of two or more substances. n The weakness of a material is compensated by the strength of other materials. n Examples

26 Composite materials: n Combined materials of two or more substances. n The weakness of a material is compensated by the strength of other materials. n Ex) Plywood 合板 Reinforced concrete 鉄筋コンクリート Fiberglass ガラス繊維 Carbon-fiber,, and so on.

27 Composite materials: n Combined materials of two or more substances. n The weakness of a material is compensated by the strength of other materials. n Ex) Plywood 合板 Reinforced concrete 鉄筋コンクリート Fiberglass ガラス繊維 Carbon-fiber,, and so on. The body of cars: formed from a fiberglass or other molded lightweight composite.

28 Composite materials: Ex) Plywood One of most common composite materials, consists of thin wood layers glued together with alternating grain direction. The weakness of a single thin sheet of wood is compensated by the strength of the neighboring sheets.

29 Composite materials: Ex) Reinforced concrete A common composite materials in which steel rods are embedded in a concrete mass. (Tensile strength + compressive strength) http-//

30 2. Electrical properties of materials A large number of different kinds of materials contribute to any electrical device. Some should be efficient to carry the electrical energy without much loss, but some should not conduct electricity so that we will not be endangered by electricity.

31 Conductors: n Conductor: any material capable of carrying electrical currents electrons can flow freely through it. Metals: the most common conductor - such as copper Saltwater: containing ions of sodium (Na+) and chlorine (Cl - ) free to move when they are part of an electric circuit

32 Conductors: n Conductor: any material capable of carrying electrical currents electrons can flow freely through it. Metals: the most common conductor - such as copper Saltwater: containing ions of sodium (Na+) and chlorine (Cl - ) free to move when they are part of an electric circuit n The arrangement of electrons in a material determines its ability to conduct electricity. Metals: loosely bonded electrons shared by many atoms, and they are free to move in an electric circuit. Metallic bonds.

33 Conductors: (cont d) n Electrical resistance: the property by which materials drain the energy away from a current. Under normal circumstances, electrons moving through a metal collide continuously with heavier ions, then their energies are converted to heat. n Electrical conductance: the inverse of electrical resistance

34 Insulators: n Insulators: materials that don t conduct electricity. (unless they are subjected to an extremely high voltage) Ex) Rocks, ceramics and many biological materials: Their electrons are bounded tightly to one or more atoms by ionic or covalent bonds.

35 Insulators: (cont d) n The primary use of insulators in electric circuits: - to channel the flow of electrons - to keep people from touching wires carrying current Ex) * Plastic materials made for power outlets, casings for car batteries, light switches. * Protective rubber boots, gloves for electrical workers. * Glass, ceramic components for isolating the current in high-power lines

36 Semiconductors: n Many materials in nature are neither good conductors nor perfect insulators. - A semiconductor carries electricity but not carry it very well - Ex) Silicon: It has much higher resistance than that of a conductor such as copper, but some of its electrons flow in an electric circuit.

37 Semiconductors: n In a silicon crystal, - a regular pattern of silicon atoms bonded by covalent bonds is displayed in the picture

38 Semiconductors: n In a silicon crystal, (cont d) - some of its electrons are taken loose by atomic vibrations, and these are free to move around and conduct electricity. Filled circle: free electron Empty circle: hole

39 solids/intrin.html Semiconductors: n In a silicon crystal, (cont d) à A defect after an electron leaves in the crystal is called a hole (a missing electron). electrons are free to move by atomic vibrations, leaving holes

40 Doped semiconductors In semiconductor production, doping intentionally introduces impurities into an extremely pure semiconductor for the purpose of modulating its electrical properties.

41 Doped semiconductors In semiconductor production, doping intentionally introduces impurities into an extremely pure semiconductor for the purpose of modulating its electrical properties. N-type P-type Electron impurity Hole impurity electrapk.com/

42 Terminology n Doped semiconductors Doping: the addition of a minor impurity to an element or compound. p-type, n-type. n Diode: one way gate of electrical currents Ex) AC à DC in electronic devices n Transistor: device to amplify and switch electronic signals and power. Simplest ex) pnp-type, npn-type n Microchips: incorporate hundreds or thousands of transistors in one integrated circuit n Digital electronic devices such as Computers and Mobile phones are made possible using microchips

43 Semiconductors: (cont d) n In semiconductors, the effects of the successive jumping of electrons from one to another conduct electricity. (Those of the hole moving through the material)

44 Superconductors: n Materials that exhibit a property known as superconductivity - the complete absence of any electrical resistance -, when they are cooled to within a few degrees of absolute zero

45 Superconductors: n If we make an electromagnet out of superconducting material and keep it cold, the magnetic field will be maintained at no energy cost except for refrigeration. à Superconducting magnets Examples

46 Superconductors: n If we make an electromagnet out of superconducting material and keep it cold, the magnetic field will be maintained at no energy cost except for refrigeration. à Superconducting magnets Ex) - Magnetic Resonance Imaging (MRI) systems for medical purpose - Magnetic levitation transportation system (homework) - Particle accelerators such as LHC at CERN in Switzerland

47 Superconductors: n How can a superconducting material allow electrons to pass through without losing energy?

48 Superconductors: n How can a superconducting material allow electrons to pass through without losing energy? Fast moving electron At very low temperature Positively charged region

49 Superconductors: n How can a superconducting material allow electrons to pass through without losing energy? - At very low temperatures, heavy ions in a material don t vibrate very much.

50 Superconductors: n How can a superconducting material allow electrons to pass through without losing energy? - At very low temperatures, heavy ions in a material don t vibrate very much. - As a fast moving electron passes between two positive ions, ions are attracted to the electron, but the electron is long gone at the time..

51 Superconductors: n How can a superconducting material allow electrons to pass through without losing energy? - At very low temperatures, heavy ions in a material don t vibrate very much. - As a fast moving electron passes between two positive ions, ions are attracted to the electron, but the electron is long gone at the time. - Nevertheless, the positive ions create a positively charged region so that the region can attract a second electron.

52 Superconductors: n How can a superconducting material allow electrons to pass through without losing energy? - At very low temperatures, heavy ions in a material don t vibrate very much. - As a fast moving electron passes between two positive ions, ions are attracted to the electron, but the electron is long gone at the time. - Nevertheless, the positive ions create a positively charged region so that the region can attract a second electron. - As far as the temperature is kept cold enough, the phenomenon is also kept forever.

53 Superconductors: n How can a superconducting material allow electrons to pass through without losing energy? Fast moving electron At very low temperature Positively charged region

54 3. Magnetic Properties of materials Q: Why some materials such as iron display strong magnetism, while other substances seem to be unaffected by magnetic fields?

55 Magnet field in an atom n We have learned that every magnetic field is due to the presence of electrical currents, thus each electron in an atom acts like a little electromagnet, and the total magnet field of the atom arises by adding those of all the tiny electron electromagnets.

56 Magnet field in an atom Each electron in an atom acts like a little electromagnet An atom in a material Atomic nucleus + - electron Magnetic field originated from orbital and spinning motion of an electron

57 Magnet field in an atom Each electron in an atom acts like a little electromagnet Magnetic field of a solid material arises from combination of all these tiny magnetic fields An atom in a material Atomic nucleus + - electron Magnetic field originated from orbital and spinning motion of an electron

58 Magnet field in an atom (cont d) n We have learned that every magnetic field is due to the presence of electrical currents, thus each electron in an atom acts like a little electromagnet and the total magnet field of the atom arises by adding those of all the tiny electron electromagnets. à Each atom in the material can be thought of as a tiny dipole magnet. à The magnetic field of a solid material like a piece 磁鉄鉱 of lodestone arises from the combination of all these tiny magnetic fields

59 n Q: However, why most materials do not have magnetic fields?

60 Magnetic Properties of materials n In ordinary situation, atomic dipole magnets point in random direction (Fig. 1), so at a place outside the material their acts tend to cancel. à nonmagnetic materials Fig.1

61 Domains Magnetic Properties of materials n In a few materials, including iron, cobalt, and nickel metals, the atomic magnets line up an effect called ferromagnetism, but orientation of domains is random. Fig.2-a

62 Domains Magnetic Properties of materials n In a few materials, including iron, cobalt, and nickel metals, the atomic magnets line up an effect called ferromagnetism, but orientation of domains is random. à No magnetic field is measured outside the material, because the small magnetic fields in different domains cancel each other. (Fig. 2-a) Fig.2-a

63 Magnetic Properties of materials n In a few materials, à In special cases, when iron cools from very high temperature in the presence of a strong magnetic field, all neighboring domains may line up. Then the material exhibits an external magnetic field permanent magnet! (Fig. 2-b) Fig.2-b Magnetic field

64 Magnetic Properties of materials n In ordinary situation, à nonmagnetic materials (Fig. 1) n In a few materials, à No magnetic field is measured outside the material (Fig. 2-a) à In special cases, in the presence of a strong magnetic field, the material exhibits an external magnetic field permanent magnet! (Fig. 2-b) Fig.1 Fig.2-a Fig.2-b Fig.3-b Domains Magnetic field http-//

65 Next topic is, Nuclear power: chapter 8