Chapter 2 Atoms and Elements. Electromagnetic Radiation. Electromagnetic Spectrum. Electron Energy Levels. 2.6 Electron Energy Levels

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1 Chapter 2 Atoms and Elements Electromagnetic Radiation 2.6 Electron Energy Levels Electromagnetic radiation Consists of energy particles called photons that travel as waves. Includes low energy particles that have long wavelengths and high energy particles that have short wavelengths. 1 2 Electromagnetic Spectrum Electron Energy Levels Electrons are arranged in specific energy levels called shells. The first energy level (n=1) contains electrons that have the lowest energy. The energy levels are labeled 1, 2, 3, and so on. 3 4 LecturePLUS Timberlake 1

2 Number of Electrons Electrons of similar energy are grouped in energy levels. The maximum number of electrons in any energy level is equal to 2n 2. n = 1 2(1) 2 = 2 n = 2 2(2) 2 = 8 n = 3 2(3) 2 = 18 n = 4 2(4) 2 = Learning Check Solution A. The correct electron shell arrangement for nitrogen is 1) 7 2) 2, 5 3) 2, 2, 3 B. The correct electron shell arrangement for sulfur is 1) 2,6 2) 8,2,6 3) 2, 8, 6 C. The element in period 3 with two electrons in the outermost energy level is 1) Mg 2) Ca 3) Be A. The correct electron shell arrangement for nitrogen is 2) 2, 5 B. The electron configuration for sulfur is 3) 2, 8, 6 C. The element in period 3 with two electrons in the outermost energy level is 1) Mg 7 8 LecturePLUS Timberlake 2

3 Learning Check Solution Indicate the number of electrons in the last electron shell for each of the following elements: Indicate the number of electrons in the last electron shell for each of the following elements: A. O 1) 4 2) 6 3) 8 A. O 2) 6 B. Al 1) 13 2) 3 3) 1 B. Al 2) 3 C. Cl 1) 2 2) 5 3) 7 C. Cl 3) Periodic Law Learning Check All the elements in a group have the same number of electrons in their outermost shells (valence electrons). Elements in a group have similar chemical and physical properties. Example: Group 2 Be 2, 2 Mg 2, 8, 2 Ca 2, 8, 8, 2 Specify if each pair has chemical properties that are similar or not similar: A. Cl and Br B. 2-5 and C. 2-4 and D. P and S E. O and S LecturePLUS Timberlake 3

4 Solution Energy Level Changes Specify if each pair has chemical properties that are 1) similar or 2) not similar: A. Cl and Br similar B. 2-5 and not similar C. 2-4 and similar D. P and S not similar E. O and S similar Electrons are in discrete energy levels. An electron absorbs energy to jump to a higher energy level. When an electron falls to a lower energy level, energy is emitted. In the visible range, the emitted energy appears as a color Learning Check Solution Answer with 1) Energy absorbed 2) Energy emitted 3) No change in energy A.What energy change takes place when an electron in a hydrogen atom moves from the first (n=1) to the second shell (n=2)? B.What energy change takes place when an electron moves from the third shell (n=3) to the second shell (n=2)? A.What energy change takes place when an electron in a hydrogen atom moves from the first (n=1) to the second shell (n=2)? Energy absorbed B.What energy change takes place when an electron moves from the third shell to the second shell? Energy emitted LecturePLUS Timberlake 4

5 Chapter 2 Atoms and Elements 2.7 Subshells and Orbitals Subshells Within each energy level, electrons are grouped into energy sublevels or subshells. All electrons in a subshell have the same energy. The different subshells are designated by the letters s, p, d, f Number of Subshells in a Shell The number of subshells in each shell is the same as the shell number. Shell Number of Types of Number Subshells Subshells n=4 4 4s, 4p, 4d, 4f n=3 3 3s, 3p, 3d n=2 2 2s, 2p n=1 1 1s Energy Levels of Subshells The s subshell has the lowest energy in any shell followed by the p, d, and f subshells. 3d n = 3 3p 3s n = 2 n = 1 2p 2s 1s LecturePLUS Timberlake 5

6 Orbitals Subshells and Orbitals An orbital is a 3 dimensional space around a nucleus in which an electron is most likely to be found. The shape represents electron density (not a path the electron follows).** Each orbital can hold up to 2 electrons. Each subshell has a specific number of orbitals. Each s subshell contains one s orbital. Each p subshell contains three p orbitals. Each d subshell contains five d orbitals. Each f subshell contains seven f orbitals s and p Orbitals Electrons in Each Subshell In an atom, all the orbitals are centered around the nucleus. For example, the illustration of the combination of s and p orbitals is LecturePLUS Timberlake 6

7 Learning Check Solution A. How many electrons can occupy a p orbital? 1) 1 2) 2 3) 3 B. How many p orbitals are in the 2p subshell? 1) 1 2) 2 3) 3 C. How many d orbitals are in the 4d subshell? 1) 1 2) 3 3) 5 D. What is the maximum number of electrons in the 3d subshell? 1) 2 2) 5 3) 10 A. How many electrons can occupy a p orbital? 2) 2 B. How many p orbitals are in the 2p subshell? 3) 3 C. How many d orbitals are in the 4d subshell? 3) 5 D. What is the maximum number of electrons in the 3d subshell? 3) Chapter 2 Atoms and Elements Electron Configuration 2.8 Electron Configurations An electron configuration Is a list of the subshells and the number of electrons in each in order of increasing energy. Contains superscripts that give the number of electrons in each subshell. Of neon is as follows: number of electrons in each subshell 1s 2 2s 2 2p LecturePLUS Timberlake 7

8 Subshell Location on the Periodic Table The periodic table contains subshell blocks arranged in order of increasing energy. Subshell Blocks There is a specific number of electrons in each subshell block. 1 s 1 s 2 p 1 p 2 p 3 p 4 p 5 p d 1 -d f 1 -f Writing an Electron Configuration An electron configuration is written by: Locating the element on the periodic table. Starting with H and writing each subshell notation and electrons in order. Some Electron Configurations First Period H 1s 1 He 1s 2 Second Period Li 1s 2 2s 1 C 1s 2 2s 2 2p 2 Third Period Na 1s 2 2s 2 2p 6 3s 1 Al 1s 2 2s 2 2p 6 3s 2 3p 1 S 1s 2 2s 2 2p 6 3s 2 3p LecturePLUS Timberlake 8

9 Electron Configurations for Atomic Numbers 1-18 Electron Configurations for Elements Noble Gas Notation Learning Check A noble gas notation is used to abbreviate the completed subshells as [noble gas]. For example, the complete configuration of bromine is 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5 Ar configuration The noble gas notation for bromine is [Ar] 4s 2 3d 10 4p 5 Using the periodic table, write the complete electronic configuration and noble gas notation for each of the following elements: A. Cl B. Sr C. I LecturePLUS Timberlake 9

10 Solution Group Numbers and Subshells A. Cl 1s 2 2s 2 2p 6 3s 2 3p 5 [Ne] 3s 2 3p 5 B. Sr 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 [Kr] 5s 2 C. I 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 5 [Kr] 5s 2 4d 10 5p 5 The Group Number is the sum of the s and p electrons in the outermost shell (valence electrons) LecturePLUS Timberlake 10