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Chapter 3 Atoms and Elements 1 Elements Elements are • pure substances that cannot be separated into simpler substances by ordinary laboratory processes • the building blocks of matter • listed on the inside front cover of this text 2 Some Elements and Their Names Names come from: • planets • mythological figures • minerals • colors • geographic locations • famous people 3 Chemical Symbols Chemical Symbols • represent name of element • consist of one to two letters and start with capital 1-Letter Symbols 2-Letter Symbols C carbon Co cobalt N nitrogen Ca calcium F fluorine Al aluminum O oxygen Mg magnesium 4 Chemical Symbols from Latin Names Ag silver, from argentum Augold, from aurum 5 Learning Check Write the correct chemical symbols for each of the following elements: A. iodine B. iron C. magnesium D. zinc E. nitrogen 6 Solution Write the symbols for each of the following elements: A. iodine = I (I2) B. iron = Fe C. magnesium = Mg D. zinc = Zn E. nitrogen = N (N2) 7 Groups and Periods On the periodic table, • elements are arranged according to similar properties • groups contain elements with similar properties in vertical columns • periods are horizontal rows of elements arranged according to atomic size 8 Periodic Table of Elements Group numbers • use the letter A for representative elements (Groups 1A–8A) • use the letter B for transition elements (Groups 3B–12B) 9 Group 1A, the alkali metals, includes lithium, sodium, potassium, rubidium, and cesium. Group 7A, the halogens, includes chlorine, bromine, and iodine. 10 Learning Check Identify the element described by the following: 1. Group 7A, Period 4 A. Br B. Cl C. Mn 2. Group 2A, Period 3 A. beryllium B. boron C. magnesium 3. Group 5A, Period 2 A. phosphorus B. arsenic C. nitrogen 11 Solution Identify the element described by the following: 1. Group 7A, Period 4 A. Br 2. Group 2A, Period 3 C. magnesium 3. Group 5A, Period 2 C. nitrogen 12 Metals, Nonmetals, and Metalloids The heavy zigzag line separates metals and nonmetals. • Metals are located to the left. • Nonmetals are located to the right. • Metalloids are located along the heavy zigzag line between the metals and nonmetals. 13 Properties of Metals, Nonmetals, and Metalloids Metals • are shiny and ductile • are good conductors of heat and electricity Nonmetals • are dull, brittle, and poor conductors • are good insulators Metalloids • are better conductors than nonmetals, but not as good as metals • are used as semiconductors and insulators • as a general rule they have the appearance of metals and the properties and characteristics of nonmetals 14 Comparing a Metal, Nonmetal, and Metalloid 15 Dalton's Atomic Theory In Dalton's atomic theory, atoms: • are tiny particles of matter • of an element are similar to each other and different from other elements • of two or more different elements combine to form compounds • are rearranged to form new combinations in a chemical reaction 16 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Rutherford's Gold Foil Experiment In Rutherford’s gold foil experiment, positively charged alpha (α ) particles were aimed at atoms of gold. Most went straight through. Occasionally one was deflected. Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close. 17 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Structure of the Atom An atom consists of • a nucleus that contains protons and neutrons • electrons in a large, empty space around the nucleus 18 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Subatomic Particles in the Atom • 1 atomic mass unit (amu) has a mass equal to 1/12 of the mass of the carbon-12 atom. • Protons have a positive (+) charge. • Electrons have a negative (–) charge. • Neutrons are neutral. • Like charges repel and unlike charges attract. 19 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Atomic Number The atomic number • is specific for each element • is the same for all atoms of an element • is equal to the number of protons in an atom • usually appears above the symbol of an element in the Periodic Table Atomic Number Symbol 11 Na 20 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Atomic Number = Protons in Atom For example, atomic number = number of protons: • Atomic number H is 1; every H atom has one proton • Atomic number of C is 6; every C atom has six protons • Atomic number of Cu is 29; every Cu atom has 29 protons 21 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Use the periodic table to fill in the atomic number, number of protons, and number of electrons for each of the following elements: (NB: atoms have zero net charge) Element Atomic Number N Protons Electrons Zn S 22 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Use the periodic table to fill in the atomic number, number of protons, and number of electrons for each of the following elements: (NB: atoms have zero net charge) Element Atomic Number Protons Electrons N 7 7 7 Zn 30 30 30 S 16 16 16 So the number of electrons will equal the number of protons for any neutral charge atom. 23 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Atomic Symbols and Subatomic Particles Examples of number of subatomic particles for atoms: Atomic symbol 16 31 O 8 8 p+ 8n 8 e- P 15 15 p+ 16 n 15 e- 65 Zn 30 30 p+ 35 n 30 e24 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Isotopes Isotopes • are atoms of the same element • have different mass numbers • have same number of protons but different numbers of neutrons Mass Numbers 24 12 Mg 25 12 Mg 26 12 Mg 25 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Naturally occurring carbon consists of three isotopes: 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the following: Isotope 12C 13C 14C protons neutrons electrons 26 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Naturally occurring carbon consists of three isotopes: 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the following: Isotope 12C 13C 14C protons 6 6 6 neutrons 6 7 8 electrons 6 6 6 27 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check 1. Which of the pairs are isotopes of the same element? 2. In which of the pairs do both atoms have 8 neutrons? 15 A. 8 B. 12 6 C. 15 7 X 15 7 X X 14 6 X X 16 8 X Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition 28 Copyright © 2012 by Pearson Education, Inc. Learning Check 1. Which of the pairs are isotopes of the same element? 12 6 B. X 14 6 X 2. In which of the pairs do both atoms have 8 neutrons? C. 15 7 X 16 8 X Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition 29 Copyright © 2012 by Pearson Education, Inc. Atomic Mass Atomic mass is the • weighted average of all naturally occurring isotopes of that element • number on the periodic table below the chemical symbol with two decimal places 30 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Calculating Atomic Mass To calculate atomic mass, • use an experimental percent abundance of each isotope of the element • multiply the percent abundance by the atomic mass of that isotope • sum the total mass of each isotope 31 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Calculating Atomic Mass To calculate atomic mass of Cl, use experimental data for both isotopes of Cl: Isotope atomic mass x % abundance 35Cl 37Cl 34.97 amu x 75.76 = 26.49 amu 100 36.97 amu x 24.24 = 8.962 amu 100 Atomic mass of Cl = 35.45 amu 32 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Electromagnetic Spectrum As frequency increases, energy increases: E = hν The electromagnetic spectrum shows the arrangement of wavelengths of electromagnetic radiation, with the visible range from 700 to 400 nm. 33 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Elements Have a Unique Atomic Spectrum When light from an element that is heated passes through a prism, it separates into a unique set of distinct lines of color called an atomic spectrum. Strontium Barium 34 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Electron Energy Levels Energy levels • are assigned numbers n = 1, 2, 3, 4, and so on • increase in energy as the value of n increases • are like the rungs of a ladder, with the lower energy levels nearer the nucleus Energy levels have a maximum number of electrons equal to 2n2. Energy level n=1 n=2 n=3 Maximum number of electrons 2(1)2 = 2(1) = 2 2(2)2 = 2(4) = 8 2(3)2 = 2(9) = 18 35 Changes in Electron Energy Level • Electrons move to a higher energy level when they absorb energy. • When electrons fall back to a lower energy level, light is emitted. • The energy emitted or absorbed is equal to the differences between the two energy levels. 36 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Electron Configurations in Periods Period 1 H 1 electron in 1st energy level. 1s1 He 2 electrons in 1st energy level. 1s2 Period 2 Energy Level 1st 2nd e- Config. Li 2 1 1s2 2s1 Be 2 2 1s2 2s2 B 2 3 1s2 2s2 2p1 C 2 4 1s2 2s2 2p2 N 2 5 1s2 2s2 2p3 O 2 6 1s2 2s2 2p4 F 2 7 1s2 2s2 2p5 Ne 2 8 1s2 2s2 2p6 37 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Electron Configurations in Periods Period 3 Energy Level Na Mg Al Si P S Cl Ar 1st 2 2 2 2 2 2 2 2 2nd 8 8 8 8 8 8 8 8 3rd 1 2 3 4 5 6 7 8 e- Config. 1s22s22p63s1 1s22s22p63s2 1s22s22p63s23p1 1s22s22p63s23p2 1s22s22p63s23p3 1s22s22p63s23p4 1s22s22p63s23p5 1s22s22p63s23p6 Period 4 Energy Level 1st 2nd 3rd 4th K Ca 2 2 8 8 8 8 1 2 [Ar]4s1 [Ar]4s2 38 Electron Configurations Beyond 20 Energy Level 1st 2nd 3rd 4th 5th 6th 7th Number of Electrons 8 18 32 32 18 8 2 39 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Electron Orbital Filling & the Periodic Table 1s22s22p2 1s22s22p63s23p64s23d2 1s22s22p63s23p6 Learning Check Write the electron configuration for the following elements: C Si O N 41 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Write the electron arrangement for the following elements: C Si = = 1s2 2s2 2p2 1s22s22p63s23p2 O As = = 1s2 2s2 2p4 1s22s22p63s23p64s23d104p3 U = [Rn] 7s26d15f3 NB: The sum of the superscripts will equal the atomic number of the element for neutral atoms. 42 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Group Number and Valence Electrons For representative elements in Groups 1A–8A, chemical properties are due to the number of valence electrons. Valence electrons are the number of electrons in the outermost energy level (the s & p electrons for that period). The group number gives the number of valence electrons for the representative elements. Group Number 1A 2A 3A 4A 5A 6A 7A 8A # Valence Electrons 1 2 3 4 5 6 7 8 43 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Electron-Dot Symbols Electron-dot symbols • are also known as Lewis structures • represent the valence electrons as dots placed on sides of symbol Possible electron-dot symbols for magnesium, with the electron arrangement of 2,8,2, • include 2 valence electrons, represented as dots • can be drawn in more than one way Mg Mg Mg Mg Mg Mg 44 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Electron-Dot Symbols for Selected Elements 45 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Question: Write the electron-dot symbol for each of the following elements: Cl, C, N. Solution: Cl C N 46 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Atomic Size Atomic size • is determined by the atom’s atomic radius, the distance between nucleus and outermost electrons • increases for representative elements from top to bottom of the periodic table • decreases within a period due to increased number of protons in nucleus 47 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Atomic Size 48 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Ionization Energy Ionization energy • is the energy required to remove one of the outermost electrons from an atom Na(g) + energy (ionization) Na+(g) + e− • decreases down a group, increases across a period from left to right 49 Metallic Character An element with metallic character is one that loses electrons easily. Metallic character • is more prevalent in metals on left side of periodic table • is less for nonmetals on right side of periodic table that do not lose electrons easily 50 Summary of Trends in Periodic Table 51 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Given the following elements: C P Cl Which is the largest atom? Which has the highest ionization energy? Which has the electron configuration 1s22s22p63s23p3 52 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Given the following elements: C Which is the largest atom? Which has the highest ionization energy? Which belongs to Group 5A? P Cl C Cl P 53 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.