1 Announcements & Agenda (01/24/07) You should currently be reading Ch 4! Quiz over Ch 3 moved to Friday! Pick up Graded Quizzes if you haven’t Welcome Visitors! Today: Recap of Mon: Electron Energy Levels (3.7) Recap of Mon: Electron Energy Levels (3.7) Periodic trends (3.3, 3.8) Periodic trends (3.3, 3.8) Start Ch 4 (Finally!) Start Ch 4 (Finally!)

2 Last Time: Medical Uses of Radiation Nuclear medicine has two main arenas Diagnostic methods Diagnostic methods Small amounts of radioisotopes administered to help image an organ or follow a physiological process Small amounts of radioisotopes administered to help image an organ or follow a physiological process Therapeutic methods Therapeutic methods Larger radiation doses to deliver fatal punch to diseased tissue Larger radiation doses to deliver fatal punch to diseased tissue

3 *EMISSION* ABSORPTION Last Time: Electrons in Atoms

4 Last Time: Explanation for Discrete Energies: the Bohr Model First model of the electron structure of atoms Gives energy levels (shells) where an electron is most likely to be found Incorrect, but a key to understanding the atom

5 Last Time: Modern Understanding of Electron Levels (Shells) Electrons are organized in shells Electrons are organized in shells Electrons in a particular shell are similar in energy and distance from nucleus Electrons in a particular shell are similar in energy and distance from nucleus Low-energy electrons closest to the nucleus Low-energy electrons closest to the nucleus Identify shells by a “principle quantum number”: 1, 2, 3, 4, 5….. Identify shells by a “principle quantum number”: 1, 2, 3, 4, 5….. The first shell (1) is lowest in energy, 2 nd level next and so on 1<2<3<4 The first shell (1) is lowest in energy, 2 nd level next and so on 1<2<3<4

6 Maximum # of electrons in any electron shell = 2n 2 n =12(1) 2 = 2 n =22(2) 2 = 8 n =32(3) 2 =18 NOTE: Electrons generally fill into shells with smallest n first; however, the filling order gets more complicated after Argon (element 18). Last Time: Number of Electrons For the first 20 electrons: Shell1234 2e8e8e2e

7 Orbitals: “Locations” of the Electrons 3-D spaces around a nucleus where an electron is most likely to be found.3-D spaces around a nucleus where an electron is most likely to be found. have shapes that represent electron density (not a path the electron follows).have shapes that represent electron density (not a path the electron follows). different shapes have different energy different shapes have different energy each orbital can hold up to 2 electrons.each orbital can hold up to 2 electrons.

8 Subshells of Orbitals Energy sublevels within principal energy level (n) Energy sublevels within principal energy level (n) All electrons in a subshell have the same energy All electrons in a subshell have the same energy Designated s, p, d, f.. Designated s, p, d, f.. Sublevel energy: s<p<d<f Sublevel energy: s<p<d<f

9 Electrons Allowed Electrons in same sublevel have same energy. Electrons in same sublevel have same energy. All 2s electrons have the same energy. All 2p electrons have the same energy which is slightly higher than the energy of the 2s electrons All 2s electrons have the same energy. All 2p electrons have the same energy which is slightly higher than the energy of the 2s electrons s sublevel 2 electrons p sublevel 6 electrons d sublevel 10 electrons f sublevel 14 electrons

10 Electrons in Energy Levels n = 1- 4 Energy Orbitals Maximum Total Level No. of Electrons Electrons 1 1s s 28 2p 6 2p 6 3 3s 218 3p 6 3p 6 3d10 3d10 4 4s 232 4p 6 4p 6 4d10 4d10 4f14 4f14

11 Organization of the Periodic Table s 1 s 2 p 1 p 2 p 3 p 4 p 5 p 6 s 1 s 2 p 1 p 2 p 3 p 4 p 5 p 6 d 1 - d 10 d 1 - d 10 f 1 - f 14

12 Periodic Law All the elements in a group have the same electron configuration in their outermost shells Outermost electrons are called valence electrons Elements with same # of valence electrons display similar chemical & physical properties!!! Example: Group 2 Be2, 2 Mg 2, 8, 2 Mg 2, 8, 2 Ca 2, 2, 8, 2

13 Groups and Periods

14 Periodic Table Note: Two methods for numbering; we will use 1A, 2A, etc.

15 Metals, Nonmetals, and Metalloids The heavy zigzag line separates metals and nonmetals. Metals are located to the left.Metals are located to the left. Nonmetals are located to the right.Nonmetals are located to the right. Metalloids are located along the heavy zigzag line between the metals and nonmetals.Metalloids are located along the heavy zigzag line between the metals and nonmetals. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

16 Metals shiny and ductileshiny and ductile good conductors of heat and electricitygood conductors of heat and electricityNonmetals dull, brittle, and poor conductorsdull, brittle, and poor conductors good insulatorsgood insulatorsMetalloids better conductors than nonmetals, but not as good as metalsbetter conductors than nonmetals, but not as good as metals used as semiconductors and insulatorsused as semiconductors and insulators Metals, Nonmetals, & Metalloids

17 More Periodic Trends How Atomic Orbital filling affects: Atomic Size (Radius) Atomic Size (Radius) Ionization Energy Ionization Energy n Definitions…. Ionization Energy : Cost of removing an e - from a neutral atom Ionization Energy : Cost of removing an e - from a neutral atom Atomic Radii: Distance between center of nucleus and outer electron shell

18 Atomic Radius Within A Group Atomic radius increases going down each group of representative elements. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

19 Atomic Radius Across a Period Going across a period left to right, an increase in number of protons increases attraction for valence electrons.an increase in number of protons increases attraction for valence electrons. atomic radius decreases.atomic radius decreases. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

20 Ionization Energy In a Group Going up a group of representative elements, the distance decreases between nucleus and valence electrons.the distance decreases between nucleus and valence electrons. the ionization energy increases.the ionization energy increases. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

21 Ionization Energy Metals have lower ionization energies.Metals have lower ionization energies. Nonmetals have higher ionization energies.Nonmetals have higher ionization energies. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

22 Chapter 4!

23 30 Good Practice Problems (Ch 4) 4.01, 4.05, 4.07, 4.09, 4.11, 4.13, 4.15, 4.17, 4.23, 4.25, 4.35, 4.37, 4.41, 4.45, 4.47, 4.49, 4.53, 4.55, 4.57, 4.59, 4.63, 4.65, 4.67, 4.69, 4.85, 4.87, 4.93, 4.97, 4.103, and 4.105

24 Chemical Bonds Attraction between two or more atoms Attraction between two or more atoms Interaction between valence electrons Interaction between valence electrons Ionic bonds Ionic bonds Covalent bonds Covalent bonds

25 An amazing thing about the universe - It works in a way that sometimes when things come together, they stick… Protons and neutrons in a atomic nuclei Atoms in molecules H H H Bonding Overview

26 TWO EXTREME CASES Ionic bonding: results when “Atom A” transfers an electron to “Atom B” (e.g. salts such as NaCl)Ionic bonding: results when “Atom A” transfers an electron to “Atom B” (e.g. salts such as NaCl) Covalent bonding: results when atoms share electronsCovalent bonding: results when atoms share electrons Polar-covalent bonding: everything in between (a good portion of ‘reality’)Polar-covalent bonding: everything in between (a good portion of ‘reality’) Chemical Bonds: attractive force holding two or more atoms together

27 Guiding Principle: The Octet Rule An octet in the outer shell makes atoms stable An octet in the outer shell makes atoms stable Electrons are lost, gained or shared to form an octet Electrons are lost, gained or shared to form an octet Electronegativity – how tightly does an atom tend to hold on to electrons? Electronegativity – how tightly does an atom tend to hold on to electrons?

28 Reminder: Valence Electrons Electrons in the highest (outer) electron level Electrons in the highest (outer) electron level Have most contact with other atoms Have most contact with other atoms Known as valence electrons Known as valence electrons Outer shells of noble gases contain 8 valence electrons (except He = 2) Outer shells of noble gases contain 8 valence electrons (except He = 2) Example: Ne 2, 8 Ar2, 8, 8

29 Electron Dot Structures Symbols of atoms with dots to represent the valence- shell electrons 1A 2A 3A 4A 5A 6A 7A 8A H  He:                       Li  Be   B   C   N   O  : F  : Ne :                                       Na  Mg   Al   Si   P   S  : Cl  : Ar :                

30 X : would be the electron dot formula for: 1.Na 2.Mg 3.Al

31 would be the electron dot formula for: would be the electron dot formula for: 1.B 2.C 3.N X