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Monday, October 15 • Lecture 12 (Thursday) – Electron Arrangement in Atoms (3.6) – Orbital Diagrams and Electron ConfiguraEons (3.7) • Lecture 13 (Today) – Orbital Diagrams and Electron ConfiguraEons (3.7) – Trends in Periodic ProperEes (3.8) – Exam 1 – RadioacEvity (4.1) Fixing Clicker Issues • When you click in during class, make sure that your clicker shows a green light • Check the list of working and non-‐working clickers • If you are in the “not working” column, re-‐register your clicker • double-‐check that your Device ID has been submiWng responses (boXom of file) Energy Levels, Sublevels, and Orbitals • Electrons can be in different energy levels (n = 1 - 7) • Each energy level contains n sublevels (1 - 4) labeled s, p, d, or f. – energy level 2 contains 2 sublevels – energy level 4 contains 4 sublevels • Each sublevel is made up of 1, 3, 5, or 7 orbitals • Each orbital can hold up to 2 electrons (of opposite spin) Electron Spin • In a magneEc field, electrons behave in 2 different ways! • The electron behaves as if it were a bundle of “spinning” charge “spin up” “spin down” Order of Filling Energy levels are filled with electrons § in order of increasing energy. § beginning with quantum number n = 1. § within an energy level, the orbitals are filled in the order s, p, d, f n = 7 n = 6 n = 5 n = 4 n = 3 n = 2 n = 1 Electron-Dot Symbols An electron-dot symbol § indicates valence electrons as dots around the symbol of the element. § of Mg shows two valence electrons as single dots on the sides of the symbol Mg. Mg Mg Mg Mg Mg Writing Electron-Dot Symbols The electron-dot symbols for § Groups 1A (1) to 4A (14) use single dots: Na Mg Al C § Groups 5A (15) to 7A (17) use pairs and single dots: P O Cl • Single/paired dots ARE NOT the same as paired/ unpaired electrons in orbital filling diagrams! # e− 6 1s 2s 2p C Groups and Electron-Dot Symbols In a group, all the electron-dot symbols have the same number of valence electrons (dots). Example: Atoms of elements in Group 2A (2) each have 2 valence electrons. Group 2A (2) · Be · · Mg · · Ca · · Sr · · Ba · Atomic Size Atomic size § is described using the atomic radius. § is the distance from the nucleus to the valence electrons. § increases going down a group. § decreases going across a period from le^ to right. Atomic Radius Ionization Energy Ionization energy § is the energy it takes to remove a valence electron from an atom in the gaseous state. Na(g) + Energy (ionization) Na+(g) + e– § decreases down a group, increasing across the periodic table from left to right. § The electron is removed from the last orbital in the electron configuration Na: 1s22s22p63s1 C: 1s22s22p2 Ionization Energy and Valence Electrons • E n e r g y The e− in 2p orbitals are: • aXracted to nucleus • repelled by 2s (and 1s) e− e− are “shielded” from the nucleus by the e− in lower energy orbitals • can also think about this as e−-‐e− repulsion ? 2pz ? 2s nuc Ionization Energy Increasing Atomic Radius; Decreasing IonizaEon Energy IonizaEon Energy Increases Decreasing Atomic Radius; Increasing IonizaEon Energy The ionization energies of § metals are low. § nonmetals are high. Ionization Energy • The ionization energy of Li > Na > K • It is very easy to remove an e- from K: it is the most reactive! Two Kinds of Atomic Symbols Isotope symbol describes a single atom mass number • idenEfies the isotope • gives the mass of the atom 12 6 symbols found in periodic table describes a typical sample made of many atoms 6 C atomic number C 12.01 Isotopes are a big part of Chapter 4… atomic mass Exam #1: Tuesday, Oct. 23rd • Exam 1 = 13% of class grade • Unexcused absence = big problems! • don’t be late • don’t miss the exam • bring a non-‐graphing, non-‐phone calculator (see syllabus) CHEM 120 So Far: The Rest of CHEM 120: • • • • • • Sig Figs Units Atoms Elements Phases of MaXer Periodic Table • RadioacEvity (Ch.4) • Chemical Bonds (Ch.5) • Chemical ReacEons (Ch.6) • Gases & SoluEons (Ch.7, 8) • ReacEon Rates (Ch.9) • Acids & Bases (Ch.10) • CHEM 220 & 221! Chapter 4: Nuclear Chemistry What is radioacEvity? What makes a substance radioacEve? How do we put radioacEve chemicals to use? Will radioacEve substances give me superpowers? (No) Radioactive Isotopes A radioactive isotope § has an unstable nucleus and usually has an atomic number above 20. § emits radiation to become more stable. § can be one or more of the isotopes of an element. § is identified by writing the mass number after the element symbol, such as iodine-131 or I-131. © 2013 Pearson EducaEon, Inc. Chapter 4, Section 1 19 Four Types of Radiation (#1 & 2) Radiation is the energy emitted by an unstable atom in the process of becoming more stable. It takes the form of § alpha particles, which are identical to a helium nucleus, § beta particles, which are high-energy electrons with a charge of 1− and a mass number of 0, © 2013 Pearson EducaEon, Inc. Chapter 4, Section 1 20 Four Types of Radiation (#3 & 4) § positron, similar to a beta particle with a charge of 1+ and mass number of 0 § gamma rays, which are high-energy radiation often emitted with other types of radiation. They are written with a mass and atomic number of 0. © 2013 Pearson EducaEon, Inc. Chapter 4, Section 1 21 Six Types of Radiation Summarized © 2013 Pearson EducaEon, Inc. Chapter 4, Section 1 22 Radiation Protection § paper and clothing for alpha particles, § a lab coat or gloves for beta particles, § a lead shield or a thick concrete wall for gamma rays, § limiting the amount of time spent near a radioactive source, or § increasing the distance from the source. © 2013 Pearson EducaEon, Inc. Chapter 4, Section 1 23 Clicker Ques-on: • Which of the following types of radia-on is the most penetra-ng (the hardest to protect yourself against)? a) b) c) d) Alpha particles Beta particles Positrons Gamma rays Fiesta Ware: RadioacEve?! • The “fiesta red” (orange-‐red) color was colored by uranium oxide • Uranium (U) has two major naturally occurring isotopes: 238 U 92 235 U 92 Fiesta Ware: colorful ceramic dinnerware 99.3 % natural abundance 0.7 % natural abundance Both U isotopes emit alpha parEcles (They undergo alpha decay) DetecHng RadiaHon: The Geiger Counter A Geiger counter § detects beta and gamma radiation. § uses ions produced by radiation to create an electrical current. • If both natural U isotopes undergo a decay, how did we detect them with the geiger counter? TOPICS U-‐238 Nucleus • U-‐238 and U-‐235 are converted to Th-‐234 and Th-‐231 by α decay! • Thorium-‐234 and Thorium-‐231 both undergo β-‐ decay! Alpha Decay When a radioactive nucleus emits an alpha particle, a new nucleus forms that has § a mass number 4 less than that of the original nucleus, and § an atomic number that has decreased by 2 from that of the initial nucleus. Completing Nuclear Equations In a completed nuclear equation, § the sum of the mass numbers of the unstable isotope and the products are equal, and § the sum of the atomic numbers of the unstable isotope and the products are equal. Sum of Mass Numbers Sum of Atomic Numbers Beta Decay When a radioactive nucleus emits an beta particle, a new nucleus forms that has § a mass number equal to that of the original nucleus, and § an atomic number that is 1 larger than that of the initial nucleus. Gamma Radiation In gamma radiation, § energy is emitted from an unstable nucleus, indicated by m following the mass number: technetium-99m, § the mass number and the atomic number of the new nucleus are unchanged Gamma radiaEon is the result of “nuclear reorganizaEon”