Lecture on atomic structure.pptx
- 1. ATOMIC STRUCTURE ATOMIC STRUCTURE CHEMICAL BONDING ELECTROMAGNETIC RADIATIONS
- 2. ATOMIC STRUCTURE Atomic Structure Models Fundamentals of Atom
- 3. CLASSICAL THEORIES Greek Philosopher, Democritus (460 BC) Suggested world was made of two things – empty space and “atomos” Atomos – Greek word for uncuttable Atoms are the smallest possible particle of matter There are different types of atoms for each material John Dalton’s Atomic Theory (1804) All matter is made of atoms Atoms of one element are all the same Atoms cannot be broken down into smaller parts Compounds form by combining atoms “Billiard Ball” model he envisioned atoms as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model them
- 8. DISCOVERY OF PROTON & NUCLEUS Eugen Goldstein (1850-1930) Using a cathode ray tube, he discovered canal rays which are beams of positively charged particles. He is credited with the discovery of protons in an atom. Ernest Rutherford - 1913 Rutherford discovered the nucleus of a gold atom with his “gold foil” experiment
- 16. ELECTRON SHELLS a) Atomic number = number of Protons /Electrons b) Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells. c) Electron shells determine how an atom behaves when it encounters other atoms
- 17. Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like to N would like to O would like to Gain 4 electrons Gain 3 electrons Gain 2 electrons
- 18. Why are electrons important? 1) Elements have different electron configurations different electron configurations mean different levels of bonding
- 21. Electron Dot Structures Symbols of atoms with dots to represent the valence-shell electrons 1 2 13 14 15 16 17 18 H He: Li Be B C N O : F :Ne : Na Mg Al Si P S :Cl :Ar :
- 22. CHEMICAL BONDING Ionic bond Covalent bond Hydrogen bond Metallic bond
- 23. CHEMICAL BONDS Chemical bonds are forces that hold the atoms together in a molecule. They are a result of strong intramolecular interactions among the atoms of a molecule The valence (outermost) electrons of the atoms participate in chemical bonds. When two atoms approach each other, these outer electrons start to interact & results in the formation of bonds between the atoms The main types of chemical bonds are ionic bond, covalent bond, hydrogen bond, and metallic bond
- 24. CHEMICAL BONDS VS ELECTRONEGATIVITY A bond between two atoms depends upon the electronegativity difference between the atoms If the electronegativity difference is significantly high, the atoms transfer electrons to form ions and thereby form an ionic bond If the electronegativity difference is zero or small, then the atoms combine to form covalent bonds.
- 26. IONIC BOND bond formed between two ions by the transfer of electrons
- 27. Formation of Ions from Metals Ionic compounds result when metals react with nonmetals Metals lose electrons to match the number of valence electrons of their nearest noble gas Positive ions form when the number of electrons are less than the number of protons Group 1 metals ion 1+ Group 2 metals ion 2+ • Group 13 metals ion 3+
- 28. Formation of Ionic Bond • Between atoms of metals and nonmetals (the electrons from metal ion transferred to non metal ion) and so ionic bond is formed. • Produce charged ions in all states. Conductors and have high melting point. • Examples; NaCl, CaCl2, K2O
- 29. 1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.
- 30. COVALENT BOND bond formed by the sharing of electrons
- 31. COVALENT BONDS atom shares one or more pairs of electrons with another atom and forms a covalent bond. This sharing of electrons happens because the atoms must satisfy the octet (noble gas configuration) rule while bonding. Such a type of bonding is common between two nonmetals. The covalent bond is the strongest and most common form of chemical bond in living organisms nonpolar covalent bond, the electrons are shared equally between the two atoms polar covalent bonds, the electrons are shared unequally between the atoms.
- 32. when electrons are shared equally NONPOLAR COVALENT BONDS H2 or Cl2
- 33. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Atom Oxygen Molecule (O2)
- 34. when electrons are shared but shared unequally POLAR COVALENT BONDS H2O
- 35. - water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.
- 36. METALLICBOND A metallic bond is a type of chemical bond in which a ‘cloud’ of free moving valence electrons is bonded to the positively charged ions in a metal. It can be described as the sharing of free electrons among a lattice of positively charged metal ions. Metal is the only substance that contains a metallic bond
- 37. Metallic Bond Formed between like atoms of metallic elements (a force that holds atoms together in a metallic substance) Such solid consists of tightly packed atoms, where the outermost electron shell of each metal atom overlaps with a large number of neighboring atoms. As a consequence, the valence electrons move freely from one atom to another. Examples; Na, Fe, Al, Au, Co
- 39. Hydrogen Bond A hydrogen bond is a chemical bond between a hydrogen atom and an electronegative atom. However, it is not an ionic or covalent bond but is a particular type of dipole-dipole attraction between molecules First, the hydrogen atom is covalently bonded to a very electronegative atom resulting in a positive charge, which is then attracted towards an electronegative atom resulting in a hydrogen bond
- 40. Hydrogen Bond: Examples • Hydrogen atom from one molecule of water bonds with the oxygen atom from another molecule. This bonding is quite significant in ice. • In chloroform (CH3Cl) and ammonia (NH3), hydrogen bonding occurs between the hydrogen of one molecule and carbon/nitrogen of another. • Nitrogen bases present in DNA are held together by a hydrogen bond
- 42. OTHER TYPES OF CHEMICAL BONDING Van der Waals Bond • Neutral molecules are held together by weak electric forces known as Van der Waals forces. Van der Waals force is a general term used to define the attraction of intermolecular forces between molecules. This type of chemical bond is the weakest of all bonds • Examples include hydrogen bond, dipole-dipole forces
- 43. OTHER TYPES OF CHEMICAL BONDING Peptide Bond • Within a protein, multiple amino acids are linked together by peptide bonds, thereby forming a long chain. • Peptide bonds are formed by a biochemical reaction that extracts a water molecule as it joins the amino group of one amino acid to the carboxyl group of neighboring amino acids • Examples include polypeptides like insulin and growth hormone.
- 44. What is radioactivity? Nuclear decay or radioactivity, is the process by which a nucleus of an unstable atom loses energy by emitting ionizing radiation. A material that spontaneously emits this kind of radiation which includes the emission of alpha particles, beta particles, gamma rays and conversion electrons
- 45. Why are elements radioactive? Unstable nucleus: • Has excess energy. • Wants to go to “ground state.” • Becomes stable by emitting ionizing radiation.
- 46. Alpha Particles (2n, 2p) Beta Particles (e- or +) Photons (hv) (x or gamma rays) Paper Concrete Radiation Types
- 47. Dr Manjunatha S, CCIS Three Common Types of Radioactive Emissions Alpha Beta Gamma
- 48. Half life and mean life Half-life is the time required for half of the atoms of a radioactive material to decay to another nuclear form. Mean life is average of all half lives
- 49. (i) Primordial Radionuclides That radionuclides that are present since the creation of earth and having long half-lives, e.g. 210Pb, 226Ra, K40 (ii) Cosmogenic Radionuclides That radionuclides that are produced in the upper atmosphere as a result of cosmic rays interaction with light particles (carbon, Nitrogen and Oxygen), e.g. C14, 7Be, 22Na, 32P, 32S (iii)Anthropogenic Radionuclides That radionuclides that are produced as a result of man-made activities such as nuclear fuel fabrication, enrichment, nuclear power generation, nuclear accidents etc., e.g. 137Cs, 134Cs, 131I, 90Sr etc. Sources of radioactivity
- 50. Units of Radioactivity • The Becquerel (Bq): Disintegration per second, dps • The curie (Ci) 1 Ci = 37,000,000,000 Bq so 1 mCi = 37 MBq; and 1 µCi = 37 kBq • rem: Rem is the term used to describe equivalent or effective radiation dose. • In the International System of Units, the Sievert (Sv) describes equivalent or effective radiation dose. One Sievert is equal to 100 rem.
- 51. Natural background radiation • The natural radiation energy from primordial radionuclides are called background radiation. • Background radiation is of terrestrial and extra-terrestrial origin. PLANTS ATMOSPHERE SOURCE (BEDROCK) MAN, ANIMALS SOILS
- 52. 1. Terrestrial radiation components • The terrestrial component originates from primordial radionuclides in the earth’s crust, present in varying amount. • Components of three chains of natural radioactive elements viz. the uranium series, the thorium and actinium series. • 238U, 226Ra, 232Th, 228Ra, 210Pb, 210Po, and 40K, contribute significantly to natural background radiation.
- 53. 2. Extra terrestrial radiation • Among the singly occurring radionuclides tritium and carbon-14 (produced by cosmic ray interactions) and 40K (terrestrial origin) are prominent. • Radionuclides from these sources are transferred to man through food chains or inhalation. 1. Terrestrial radiation components contd… • The extra terrestrial radiation originates in outer space as primary cosmic rays. • The primary cosmic rays mainly comprise charged particles, ionised nuclei of heavy metals and intense electromagnetic radiation.
- 54. 3. Artificial Radionuclides • Over the last few decades man has artificially produced hundreds of radionuclides. • Artificial radioisotopes to the atmosphere during the course of operation of the nuclear fuel cycle, nuclear tests (mainly atmospheric) and nuclear accidents • Most of the artificial radioisotopes decay -short half-lives. Therefore only a few of them are significant from the point of human exposure.
- 55. Radon • Radon is a radioactive gas decay product of radium, created during the natural breakdown of uranium in rocks and soils • It is one of the heaviest substances that remains a gas under normal conditions and is considered to be a health hazard causing cancer • It has three isotopes, namely, 222Rn (238U), 220Rn (232Th) and 219Rn (235U). 222Rn has longer half life (3.84 days) than the other two isotopes
- 56. Sources of background radiation
- 57. Dr Manjunatha S, CCIS Radioactivity – is it a health problem? • The Alpha, Beta and Gamma particles all add energy to the body’s tissues. The effect is called the Ionizing Energy. It can alter DNA. • Even though Alpha particles are not very penetrative if the decaying atom is already in the body (inhalation, ingestion) they can cause trouble.
- 58. Biological Effects: Mechanisms of Injury Ionizing Radiation Cell Death Cell Damage Repair Transformation
- 59. External Dose Radiation Dose Dose or radiation dose is a generic term for a measure of radiation exposure. In radiation protection, dose is expressed in millirem. X-Ray Machine Image (film) After Radiation dose (single chest x ray = 5-10 mrem).
- 60. Contamination Contamination is the presence of a radioactive material in any place where it is not desired, and especially in any place where its presence could be harmful. Yuck!
- 61. The radium dial painters • Watch-dial painters - United States Radium factory in Orange, New Jersey, around 1917 . • The Radium Girls (4000) were female factory workers who contracted radiation poisoning from painting watch dials withself- luminous paint. • They were used to tip (i.e., bring to the lips) their radium-laden brushes to achieve a fine point. • Unfortunately this practice led to ingested radium, and many of the women died of sicknesses related to radiation poisoning. • The paint dust also collected on the workers, causing them to “glow in the dark.” • Some also painted their fingernails and teeth with the glowing substance.
- 63. Who’s the Famous “Madame” of Radiological Fame? Marie Curie • With her husband Pierre, discovered radium and coined the term “radioactive” • First woman to win two Nobel Prizes
- 64. 64 Medical Applications Radioisotopes with short half- lives are used in nuclear medicine because they have the same chemistry in the body as the nonradioactive atoms. • In the organs of the body, they give off radiation that exposes a scan giving an image of an organ. Thyroid scan
- 65. Space Exploration Radioisotope Thermoelectric Generator (RTG) If two dissimilar metals were joined at two locations that were maintained at different temperatures, an electric current would flow in a loop. In an RTG, the decay of a radioisotope fuel provides heat to the “hot” junction, while the other junction uses radiation heat transfer to outer space to maintain itself as the “cold” junction.
- 66. Space Exploration The fuel in: • Satellites • Jupiter Probe • Others Jupiter Probe
- 67. Power Generation Nuclear power supplies 7.5% of electricity generated in Pakistan Currently, 6 power plants are operating Photo by Karen Sheehan
- 68. Nuclear Medicine Diagnostic Procedures • Short half-life radioactive injection • Pictures taken with special gamma camera • Many different studies: Thyroid Lung Cardiac White Blood Cell Photo by Karen Sheehan
- 69. Bone Scans Image courtesy of
- 70. Radiation Therapy Used for treating cancer. External Beam Brachytherapy (implants) Image courtesy of Photo by Karen Sheehan
- 71. - Higher yielding - Disease-resistance - Well-adapted - Better nutrition Mutant cultivars Crop improvement by mutation techniques no mutation negative mutation
- 72. - Improving crop cultivation - Enhancing biodiversity - Increasing farmer’s income Mutation techniques
- 73. Preservation of food and agricultural product by radiation An alternate method of food preservation by irradiation of X ray or gamma rays. It is used to prolong the shelf life of many food and agricultural products, destroy bacteria and microorganisms in food (pre packed or bulk) and grains(rice, corn..). The food exposed to controlled amount of ionizing radiation in shielded area for a specific time to achieve desirable objectives. The sources are gamma rays from Cobalt 60 or Cesium 137 etc
- 74. Dentures • Uranium is added to false teeth to provide a shine to the material (about 10% of the teeth) • Concentration of uranium is quite low – about 300 parts per million
- 75. Radiation Detection Instruments Geiger Counter Liquid Scintillation Counter Photo by Karen Sheehan Photo by Carl Tarantino
- 76. Annual Radiation Dose Limits General Public vs. Occupational Established by the Nuclear Regulatory Commission • General Public Limit - 100 mrem • Occupational Limit - 5,000 mrem Remember – We get approximately 300 mrem per year from natural background exposure.
- 78. Electromagnetic Waves and Material Interactions EM Spectrum
- 79. Light, microwave, x-ray, TV, and cell phone transmission are all kinds of electromagnetic waves. Electromagnetic waves are a group of energy waves that are mostly invisible and can travel through empty space. These energies bombard our bodies all day long, but we are only aware of a very small portion of them: visible light (colors), infrared light (heat), and ultraviolet (sunburn).
- 81. Electromagnetic energy is created by vibrations that produce waves. Each electromagnetic wave emits a different level of energy. These energies travel silently at the speed of light and produce a “signature” wave – with a unique range of length, energy, and frequency – that scientists can identify and measure.
- 82. We can measure the energy of an electromagnetic wave by measuring its frequency. Frequency refers to the number of waves a vibration creates during a period of time. In general, the higher the frequency, or number of waves, the greater the energy of the radiation.
- 83. When we use the term “light”, we are referring to a group of electromagnetic waves called visible light. Each individual wavelength within the spectrum of visible light wavelength represents a particular color. When light of that particular wavelength strikes our eye, we perceive that specific color sensation.
- 84. Another popular group of waves from the electromagnetic spectrum involves infrared. Infrared radiation is a type of electromagnetic radiation that involves heat, or thermal radiation. All objects emit (give out) and absorb (take in) thermal radiation.
- 85. When light interacts with objects, it is either absorbed, reflected, transmitted, or refracted. Absorption – The loss of light as it passes through a material. Refraction – The bending of light as they pass between mediums. Transmission – The passage of light through a material. Reflection – The return of light by a material.
- 86. Let’s look at an example of absorption… When you go to the dentist, one of the first things they do is obtain an x-ray of you. Unnecessary exposure of x-ray radiation can be harmful, so doctors try to minimize the area that those electromagnetic waves interact with your body by making you wear special protective clothing.
- 87. What do these special clothes do? These protective clothes contain some amount of a dense element, lead, in them. The high density of this element allows x-rays to be absorbed by atoms in lead, decreasing the energy of the x-rays. Lead, in turn, shields your body from unnecessary radiation by absorbing x-rays. Only the upper body was imaged because x-rays hitting the lower torso were absorbed by the lead apron.
- 88. Another example of absorption of electromagnetic waves in our daily lives involve the use of a microwave. Microwaves are widely used to quickly heat up food. Microwaves are also referred to as range of waves in the electromagnetic spectrum with a specific wavelength and frequency.
- 89. How do microwaves heat up food? Microwaves utilize the fact that food contains water molecules. When a microwave is turned on, the energy from microwaves is absorbed by water molecules in food, making them vibrate. These vibrations give off heat, which warms up your food. Water molecules absorb the microwaves, giving off heat as the molecules vibrate.
- 90. Let’s look at an example of reflection… Reflection occurs when light is returned by an object. Although many objects reflect light, common examples include mirrors and smooth water surfaces.
- 91. How does an object reflect light in a mirror? Reflection involves two rays, an incoming (incident) ray and an outgoing (reflected) ray. When an incoming ray strikes a mirror, the ray changes direction. This ray is now reflected off the mirror. The angle of incident rays and the angle of reflected rays are equal in all reflected light of smooth objects.
- 92. Reflection can also involve scattering of light… When light strikes an object that has a rough surface, the light scatters everywhere instead of bouncing off at equal angles.
- 93. Let’s look at an example of transmission… Transmission of light is the passing of light through an object. Objects have different levels of transmission. Opaque objects reflect or absorb all light, so you won’t be able to see behind opaque objects. Translucent objects allow only a part of the light through, letting you slightly see behind the object. Transparent objects pass all light through.
- 94. Why are shadows formed? Shadows are formed when light is blocked by an object. Shadows are produced when light hits an opaque object which prevents the light beams from passing through. The light beams are absorbed by the object and cast a shadow.
- 95. Let’s look at an example of refraction… Refraction involves bending of light as it passes from one substance to another. A common example of refraction can be observed when you go fishing. Due to refraction, you perceive things that aren’t located in the proper location.
- 96. Why does refraction happen? The bending of light is due to a change in its speed. When light passes from a less dense substance (such as air) to a more dense substance (such as water), it slows down and bends into the more dense material. On the other hand, when light passes from water to air, it speeds up and bends outwards.
- 97. Light interaction with objects can involve combinations of absorption, reflection, transmission, and refraction. A common example that has both absorption and reflection involves clothes. If you are wearing blue jeans, you see the color blue because the jeans absorb all other colors but reflect blue.
- 98. Electromagnetic waves can also change the temperature of an object. Earlier, we saw an example of how microwaves can heat up food. Other electromagnetic waves can be used to change temperature of an object. As mentioned before, infrared radiation is a type of electromagnetic radiation that involves heat. When infrared waves come in contact with an object, the waves transfer heat to that object. Temperature inside the house increased due to heating from the sun.
- 99. Materials are chosen for specific applications due to their special properties. Materials that conduct heat readily are called thermal conductors. Materials that limit heat transfer are called thermal insulators. Materials that allow flow of electrical current are called electrical conductors. Materials that limit the flow of electrical currents are called electrical insulators.
- 100. Conduction involves transferring heat between substances that are in direct contact with each other. Good thermal conductors include metals such as aluminum, steel, and copper. Good thermal insulators include nonmetals such as rubber, wood, and styrofoam.
- 101. A popular example of conduction can be found in cooking. When a pot is on the stove, heat is transferred from the stove to the pot. The pot is made of metal, so it is a good thermal conductor. Most pots have a handle made of rubber so you don’t feel heat when you pick up a pot from the handle. This is because rubber is a good thermal insulator and doesn’t allow heat to be transferred to the handle.
- 102. Materials can expand or contract due to presence or absence of of heat. Thermometers are a great example that involve substances expanding and contracting due to varying temperature. Thermometers contain a special liquid, mercury, which is a good thermal conductor. The mercury molecules expand and get bigger as it gets warmer and get smaller as it cools down. This results in the liquid moving up when it’s warm, and drop down when it’s cold. The molecules expand as it gets warmer because the volume of the liquid increases as it’s heated and slowly decreases as it’s cooled.
- 103. Materials are also chosen for their electrical properties. Most metals are good conductors of electrical current. Metals allow electrons to flow easily from one atom to another. Therefore, metals are commonly used in todays devices such as computers, phones, and TVs. Electrical insulators do not let electrons flow easily from one atom to another. Electrical insulators are used to protect us from dangerous effects of electricity flowing through conductors. Good electrical insulators include nonmetals such as rubber, air, and wood.
- 104. Summary Electromagnetic Waves – Group of energy waves that are mostly invisible and can travel through empty space. Frequency – Number of waves a vibration creates during a period of time. Visible Light – Range of electromagnetic spectrum that can be detected by eys Infrared – Type of electromagnetic radiation that involves heat. Absorption – The loss of light as it passes through a material. Reflection – The return of light by a material. Transmission – The passage of light through a material. Refraction – The bending of light as they pass between mediums. Translucent – Allow only a part of the light through. Opaque – Reflect or absorb all light. Thermal Conductors – Materials that conduct heat readily. Thermal Insulators – Materials that limit heat transfer. Electrical Conductors – Materials that allow flow of electrical current.