5. A chemical reaction involves either the union or separation of individual atoms. (~1808)

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1 Atomic Structure & Elements On-line: _(Bennett)/Chapters Read (and scan 3.1, ). See video tutorials- Atoms & Elements, part 0, 1a, 1b and scan as needed Nuclear Chemistry- parts 1, 4 & Chapter 2 (pages ) Lab Manual Appendix III: Parts F & G Picture of an Atom Nucleus I. Dalton s Atomic Theory 1. All matter is made up of atoms. 2. Atoms can neither be created nor destroyed. 3. Atoms of a particular element are alike in properties like mass. 4. Atoms of different elements are different from one another. Electron Cloud 5. A chemical reaction involves either the union or separation of individual atoms. (~1808) II. Subatomic particles Particle Symbol Charge Relative Mass (amu) Date of discovery protons p neutrons n electrons e Compare charges and relative mass. An amu or atomic mass unit is a convenient relative mass unit, because a proton and neutron each have a mass of about 1 amu. 1 amu = x g. III. How p +, n, and e fit together in atoms & ions A. p + & n are bound together in the nucleus, located in the center of the atom. Note: The p + number = and What is in the nucleus of the most common form of the lithium (Li) atom? Note: 7 Li means that the sum of the p + and n in the nucleus is 7. Key proton 7 Li nucleus neutron 1

2 B. Analogy for size of nucleus relative to the whole atom: The whole atom is the size of a major league baseball park. The nucleus would be like a marble sitting out past second base. This means: 1. Nucleus: very small & dense. (Does something about the nucleus bother you?) 2. Most of the atom s space is occupied by e, which have very little mass. C. The Bohr model (planetary) 1. Electrons (e - ) are found in specific orbits (or shells.) 2. Shells closer to the nucleus have energy. 3. So electrons (e ) in orbits farther from the nucleus are bound. 4. Electrons can jump from one shell to another but can never be between shells or possess any energies in between. A D. Symbolism: Z E Example for carbon with 6 neutrons is 6 C 1. E = elemental symbol, 2. A = the mass number (sum of the number of protons + neutrons.) 3. Z = E. Isotopes 1. Atoms that have the (ie the same atomic number), but a different number of neutrons (ie different mass number.) 2. Many atoms have isotopes, some of which are more stable than others. 3. Example: isotopes of carbon: C, 13 C, 14 C C is the most abundant isotope. 14 C is radioactive. (Used in determining age of old objects.) C 13 C 14 C p + n e 4. Neutrons are thought to act as a kind of glue that holds the protons and neutrons together. Otherwise the protons would repel each other. 2

3 IV. Looking at the elemental symbols on the periodic table. A. For example, look at carbon on the Periodic Table: 1. The atomic number is. 2. The atomic weight is.011amu and is the weight of the average C atom on earth. Remember: The atomic mass unit (amu) is a convenient unit, defined relative to a C atom. One atom of C is defined to weigh.0000 amu. Are the atomic mass and mass number the same thing? B. Instruments like the mass spectrometer allow chemists to make accurate determinations of the weight and abundance of the different isotopic forms of an element. C. Carbon isotopic mass & abundance data: isotope abundance (%) mass (amu) C C source: CRC Handbook, 59 th ed. D. Qualitative Atomic Mass: The weight of the average atom should be quite close to (since most of the C atoms are C), but a little bit above (because there are some 13 C atoms which weigh more than amu.) E. Quantitative Atomic Mass: Calculation of the average weight C component: amu 98.89/100 = amu 13 C component: amu 1.11/100 = amu + average weight is amu This is close to the.011 amu atomic weight value in Periodic Table. The % abundance is also called the natural abundance. Do you think the natural abundance values on earth are the same as those on other planets, meteors, asteroids, etc.? V. Quantum mechanics A. Describes atomic behavior better than Bohr model. (Bohr model only works well for H atoms) 3

4 B. This model views e as waves instead of particles. Think of an electron as a cloud of negative charge. C. Uses a specific mathematical approach (requires very advanced math) that gives a model with much better predictive capabilities. D. We will use results from quantum mechanics. VI. Atomic orbitals (where e hang out) A. Principal quantum numbers: 1, 2, 3, etc.. Describes levels or shells around the nucleus (correlates to period numbers on the periodic table) Shells Orbitals 1 (smallest shell) one 1s 2 one 2s, three 2p 3 one 3s, three 3p, five 3d 4 one 4s, three 4p, five 4d, seven 4f B. Orbital shapes: (see the Orbitron at 1. orbitals are one lobed and spherical 2. orbitals are 2 lobed and are roughly dumbbell shaped. 3. and orbitals have relatively complicated shapes. C. Energies You might consider that all of the orbitals of an atom (up to and beyond 7f) always exist, but only become interesting when they are occupied by e. Orbital occupancy by e - : 1. Lowest energy orbitals (those closest to nucleus) are occupied first. 2. An orbital can only contain. 3. When orbitals of equal energy (ex.: 2px, 2py, 2pz) are being filled, put one e in each orbital first, then add start adding additional e. D. We describe the orbital occupancy of an atom (or ion) by drawing an orbital filling diagram and by writing its electronic configuration. In this class you will do this by direct application of the Periodic Table. 4

5 (First, you should number the periods (rows) on the left, 1-7. These numbers are the period number and also refer to the principle quantum number.) Periodic Table 1A 8A 1 2 H He A 3A 4A 5A 6A 7A < Atomic number Li Be < Elemental symbol B C N O F Ne < Atomic weight Na K Rb Cs Fr (223) Mg B 4B 5B 6B 7B < B > 1B 2B 20 Ca Sr Ba Ra Sc Y La Ac (227) 22 Ti Zr Hf Rf (261) 23 V Nb Ta Ha (263) 24 Cr Mo W Sg (263) 25 Mn Tc (98) 75 Re Ns (265) 26 Fe Ru Os Hs (265) 27 Co Rh Ir Mt (266) 28 Ni Pd Pt (269) 29 Cu Ag Au (272) 30 Zn Cd Hg (277) 13 Al Ga In Tl Si Ge Sn Pb P As Sb Bi S Se Te Po (209) 17 Cl Br I At (210) 18 Ar Kr Xe Rn (222) 58 Ce Pr Th Pa Nd U Pm (145) 93 Np Sm Pu (244) 63 Eu Am (243) 64 Gd Cm (247) 65 Tb Bk (247) 66 Dy Cf (251) 67 Ho Es (252) 68 Er Fm (257) 69 Tm Md (258) 70 Yb No (259) 71 Lu Lr (260) E. Let s try a few. (Remember: Elemental identity is determined by p + number.) 1. How many electrons are there in a hydrogen (H) atom, and in which orbitals are the electrons found? Draw an orbital filling diagram (on the back?) Write the electronic configuration. 2. Write the electronic configuration for helium, He. For lithium, Li For beryllium, Be For boron, B For carbon, C For nitrogen, N 5

6 For oxygen, O. For fluorine, F For neon, Ne For sodium, Na For magnesium, Mg For phosphorous, P For calcium, Ca For iron, Fe For selenium, Se E. Important definition: The outermost s and p electrons are called valence electrons. Because they are outermost, they can be involved in sharing (covalent bond formation) or they may be lost or gained (in ion formation). Underline the valence electrons in the examples, above. 1A 1A H Periodic Table of the Elements: Orbital Blocks 2A 3B 4B 5B 6B 7B 8B 1B 2B 3A 4A 5A 6A 7A 8A He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Tc Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Lilac = filling s orbitals Center, Yellow = filling d orbitals Right, Green = filling p orbitals VII. Development of the Periodic Table (Mendeleev) This discussion is important in helping you understand how science works and why humans have found it useful. 6

7 A. Origin: Mendeleev organized the elements into a table based on chemical & physical properties & atomic weight (Note: Protons ( p + ) had not yet been found). 1. He arranged the table so that atoms in a column had similar chemical and physical properties: CH 4 NH 3 H 2 O HF SiH 4 PH 3 H 2 S HCl HBr 2. And so that atomic weight increases as you move from left to right across the table. That is, F weighs more than O, O weighs more than N, etc. 3. And so that atomic weight increases as you move from top to bottom. That is, Cl weighs more than F, Br weighs more than Cl. B. When he did this, he saw 1. He thought the were elements that existed that had not yet been discovered. 2. For the gap below silicon, he made very specific predictions (interpolation) of the properties of this undiscovered element. He called this undiscovered element, Eka-silicon. Periodic Table of the Elements Known in Mendeleev s Time H Li Be Na Mg B C N O F Al Si P S Cl K Ca Ti V Cr Mn Fe Co Ni Cu Zn As Se Br Sr Y Zr Nb Mo Rh Pd Ag Cd Sn Sb Te I Ba Ta W Os Ir Pt Au Hg Pb Bi Note: Some of the lanthanides & actinides were known by 1839, but these groups have been omitted for clarity. Mendeleev was able to use the elements shown above to make some striking predictions based on periodicity. Known since ancient times (C, S Fe, Cu, Ag, Sn, Au, Hg, Pb) Discovered in the Middle Ages (P) Discovered Date source: 7

8 C. About 15 years after his prediction, Eka-silicon (Ge) was discovered & found to have properties very close to those he predicted. Predicted for eka-silicon Measured for Ge Atomic wt Density (g/cm 3 ) Density Cl (g/cm 3 ) compound from Chemistry 3 rd ed., Atkins & Jones Scientists were impressed by the predictive power of Mendeleev s ideas!!! D. Why are elements in the same column in the Periodic Table similar in their chemical reactivity? 1. Representative elements in the same column have the. 2. Because of this they tend: a) to form the same types of ions b) to have similar (not identical). E. Another way to look at the elements in the periodic table: 1. Metals Examples: Mg, Cr, Fe, Cu, Co, Au, Zn, Ag, Ni, Ti, Na, Li, Ca, Ba a) Most tend to lose e b) Conduct heat & electricity well c) Shiny, form into thin sheets & wires, etc. 2. Non-metals Examples: C, N, O, F, S, P, Br, Cl, He, Ne a) Most tend to. b) Often don t conduct heat & electricity well 3. Metalloids have intermediate properties. Examples: Si, As, Sb, Ge, Te 8

9 Modern Periodic Table of the Elements * 1A 1 H A 3A 4A 5A 6A 7A 8A 2 He Li Be < < < Atomic number Elemental symbol Atomic weight 5 B C N O F Ne Na Mg B 4B 5B 6B 7B < B > 1B 2B 13 Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc (98) 44 Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po (209) 85 At (210) 86 Rn (222) 87 Fr (223) 88 Ra Ac (227) 104 Rf (261) 105 Ha (263) 106 Sg (263) 107 Ns (265) 108 Hs (265) 109 Mt (266) 110 Ds (269) 111 Rg (272) 1 Cn (277) 58 Ce Pr Nd Pm (145) 62 Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu (244) 95 Am (243) 96 Cm (247) 97 Bk (247) 98 Cf (251) 99 Es (252) 100 Fm (257) 101 Md (258) 102 No (259) 103 Lr (260) *Organized by increasing number of protons rather than atomic weight. Indicate the metals, non-metals and metalloids on the periodic table above. VIII. Radioactivity A. The nucleus of some atoms is not stable. There are too many or too few protons for the number of neutrons. B. The unstable nucleus releases so it can become more stable. 1. Many elements have stable and radioactive isotopes. ( C and 14 C) 2. All isotopes of elements with atomic # equal to or greater than are radioactive. C. Common types of radioactive particles 4 Alpha (α) particles - 2 protons and 2 neutrons, 2He Beta (β) particles electron, -1 0 e Positron - electron but with a positive charge, Gamma (γ) rays - (no mass) high energy radiation D. Biological effects of ionizing radiation. 1. Radiation causes atoms and molecules to lose electrons and become ions. 2. These cations can react in ways that disrupt the normal processes of a cell e 9

10 3. Damage to DNA can lead to mutations or cell death. 4. Rapidly dividing cells are most sensitive to radiation damage. 5. Damage to the DNA in sperm or eggs cells can cause inherited damage. E. Protection from Radiation 1. ALARA, as low as reasonably achievable. 2. Time. Minimize the time exposed. 3. Distance. Maximize distance. Exposure decreases with the square of the distance. So doubling the distance decreases the exposure to ¼ the level. 4. Shielding. Appropriate shielding greatly reduces the exposure. 5. Not all ionizing radiation has the same amount of energy. 6. Penetration of particle depends on energy, mass and charge. Type Penetration Shielding Ability to ionize α-particles a sheet of paper, clothing β-particles intermediate, thick plastic, lead apron penetrates skin γ-rays high, can pass thru your body thick layer of lead or concrete α-particles can be stopped by your clothing or skin. But if they are inhaled, ingested or by some other method internalized, α-particles can be very harmful. 7. Monitoring Dosage a) Important as radiation is cumulative b) Film badges, Geiger counters c) Many different units: curie, gray, rad, rem, etc Occupational dose limit, 5 rem/year Average dose for Americans, 0.62 rem, (half from background sources) F. Half Life the time it takes for ½ the atoms in a sample to decay (fraction of a s to 10 9 y) 14 C 5730 y 3 H.3 y 3 I 13.2 h G. Some Medical Uses 1. Treatment to kill cancer cells, examples Radiation with 60 Co, also written cobalt-60 Brachytherapy, implants of radioactive material Temporary implants with Ir-192 and Cs-137. Permanent implants with Pd-103 and I-5 2. Diagnostic tests (examples) Imaging bone, kidney, breast tumor with Technetium-99m Thyroid imaging and uptake, I-3, I Videos about atoms and radiation (Good except deuterium is not radioactive as it says at ~2:45 in the video.) 10

Nucleus. Electron Cloud

Nucleus. Electron Cloud Atomic Structure I. Picture of an Atom Nucleus Electron Cloud II. Subatomic particles Particle Symbol Charge Relative Mass (amu) protons p + +1 1.0073 neutrons n 0 1.0087 electrons e - -1 0.00054858 Compare