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Chapter 3 Atoms and Elements Matter 3.1 Classification of Matter Matter is the “stuff” that makes up all things. Copyright © 2009 by Pearson Education, Inc. Copyright © 2009 by Pearson Education, Inc. 1 Pure Substances 2 Elements Elements are • pure substances that contains atoms of only one type. A pure substance is classified as • matter with a specific composition. • an element when composed of one type of atom. • a compound when composed of two or more Copper, Cu Lead, Pb Aluminum, Al elements combined in a definite ratio. Copyright © 2009 by Pearson Education, Inc. 3 Compounds 4 Elements in a Compound Compounds “Table salt” is a compound that contains the elements sodium and chlorine. • contain two or more elements in a definite ratio. Salt (NaCl) Table sugar (C12H22O11) Water (H2O) Copyright © 2009 by Pearson Education, Inc. 5 6 Mixtures Physical Separation of a Mixture A mixture is a type of matter that consists of • two or more substances that are physically mixed, not chemically combined. • two or more substances in different proportions. • substances that can be separated by physical methods. Example: Pasta and water are separated with a strainer. Copyright © 2009 by Pearson Education, Inc. 7 Homogeneous Mixtures 8 Heterogeneous Mixtures In a homogeneous mixture, In a heterogeneous mixture, • the composition of substances is not uniform. • the composition varies from one part of the mixture to another. • the different parts of the mixture are visible. • the composition is uniform throughout. • the different parts of the mixture are not visible. Copyright © 2009 by Pearson Education, Inc. Copyright © 2009 by Pearson Education, Inc. 9 Classification of Matter 10 Learning Check Identify each of the following as a pure substance or a mixture. A. pasta and tomato sauce B. aluminum foil C. helium D. air 11 12 Solution Learning Check Identify each of the following as a pure substance or a mixture. Identify each of the following as a homogeneous or heterogeneous mixture: A. pasta and tomato sauce mixture A. hot fudge sundae B. aluminum foil pure substance B. air C. helium pure substance C. sugar water D. air mixture D. peach pie 13 14 Chapter 3 Solution Identify each of the following as a homogeneous or heterogeneous mixture: A. hot fudge sundae heterogeneous mixture B. air homogeneous mixture C. sugar water homogeneous mixture D. peach pie heterogeneous mixture Atoms and Elements 3.2 Elements and Symbols Copyright © 2009 by Pearson Education, Inc. 15 Elements 16 Sources of Some Element Names Elements are • pure substances that cannot be separated into • Some elements are named for planets, mythological figures, minerals, colors, scientists, and places. simpler substances by ordinary laboratory processes. the building blocks of matter. gold carbon aluminum 17 18 Symbols of Elements Symbols from Latin Names A symbol • represents the name of an element. • consists of 1 or 2 letters. • starts with a capital letter. 1-Letter Symbols C carbon N nitrogen F fluorine O oxygen Mg Several symbols are derived from Latin names as shown below. 2-Letter Symbols Co cobalt Ca calcium Al aluminum magnesium Cu, copper (cuprum) Au, gold (aurum) Fe, iron (ferrum) Ag, silver (argentum) Copyright © 2009 by Pearson Education, Inc. 19 Physical Properties of Elements Physical Properties of Elements The physical properties of an element • are observed or measured without changing its identity. • include the following: Shape Color Odor and taste 20 Some physical properties of copper are: Color Luster Melting point Boiling point Conduction of electricity Conduction of heat Density Melting point Boiling point Red-orange Very shiny 1083 °C 2567 °C Excellent Excellent 21 Learning Check Copyright © 2009 by Pearson Education, Inc. 22 Solution Select the correct symbol for each. A. Calcium 2) Ca Select the correct symbol for each. A. Calcium 1) C 2) Ca 3) CA B. Sulfur 1) S 2) Sl 3) Su B. Sulfur 1) S C. Iron 1) Ir 2) FE 3) Fe C. Iron 3) Fe 23 24 Learning Check Solution Select the correct name for each symbol. A. N 1) neon 2) nitrogen 3) nickel Select the correct name for each: A. N 2) nitrogen B. P 1) potassium 2) phlogiston 3) phosphorus B. P 3) phosphorus C. Ag 1) silver 2) agean 3) gold C. Ag 1) silver 25 Chapter 3 Atoms and Elements 26 Groups and Periods 3.3 The Periodic Table 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. Copyright © 2009 by Pearson Education, Inc. 27 Groups and Periods 28 Periodic Table Copyright © 2009 by Pearson Education, Inc. 29 30 Names of Some Representative Elements Group Numbers Group Numbers • use the letter A for the representative elements (1A to 8A) and the letter B for the transition elements. • also use numbers 1-18 to the columns from left to right. 31 Alkali Metals 32 Halogens Group 1A (1), the alkali metals, includes lithium, sodium, and potassium. Group 7A (17), the halogens, includes chlorine, bromine, and iodine. Copyright © 2009 by Pearson Education, Inc. Copyright © 2009 by Pearson Education, Inc. 33 Learning Check Solution Identify the element described by the following: A. Group 7A (17), Period 4 1) Br 2) Cl 34 A. Group 7A (17), Period 4 1) Br B. Group 2A (2), Period 3 3) Mn 3) magnesium B. Group 2A (2), Period 3 1) beryllium 2) boron 3) magnesium C. Group 5A (15), Period 2 1) phosphorus 2) arsenic 3) nitrogen C. Group 5A (15), Period 2 3) nitrogen 35 36 Metals, Nonmetals, and Metalloids on the Periodic Table 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. 37 Properties of Metals, Nonmetals, and Metalloids 38 Comparing a Metal, Metalloid, and Nonmetal 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. 39 Learning Check 40 Solution Identify each of the following elements as 1) metal, 2) nonmetal, or 3) metalloid. Identify each of the following elements as 1) metal, 2) nonmetal, or 3) metalloid. A. sodium B. chlorine C. silicon D. iron E. carbon A. sodium B. chlorine C. silicon D. iron E. carbon ____ ____ ____ ____ ____ 41 1 metal 2 nonmetal 3 metalloid 1 metal 2 nonmetal 42 Learning Check Solution Match the elements to the description. Match the elements to the description. A. Metals in Group 4A (14) 1) Sn, Pb 2) C, Si 3) C, Si, Ge, Sn A. Metals in Group 4A (14) 1) Sn, Pb B. Nonmetals in Group 5A (15) 1) As, Sb, Bi 2) N, P 3) N, P, As, Sb B. Nonmetals in Group 5A (15) 2) N, P C. Metalloids in Group 4A (14) 1) C, Si, Ge, 2) Si, Ge 3) Si, Ge, Sn, Pb C. Metalloids in Group 4A (14) 2) Si, Ge 43 Chapter 3 Atoms and Elements 44 Dalton’s Atomic Theory 3.4 The Atom In Dalton’s atomic theory, atoms • are tiny particles of matter. • of an element are similar 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. Copyright © 2009 by Pearson Education, Inc. 45 Subatomic Particles Rutherford’s Gold Foil Experiment Atoms contain subatomic particles. • • • • 46 In Rutherford’s gold foil experiment, positively charged particles • were aimed at atoms of gold. • mostly went straight through the atoms. • were deflected only occasionally. Protons have a positive (+) charge. Electrons have a negative (-) charge. Neutrons are neutral. Like charges repel and unlike charges attract. Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close. 47 48 Rutherford’s Gold Foil Experiment Structure of the Atom An atom consists • of a nucleus that contains protons and neutrons. • of electrons in a large, empty space around the nucleus. Copyright © 2009 by Pearson Education, Inc. Copyright © 2009 by Pearson Education, Inc. 49 Atomic Mass Scale 50 Particles in the Atom On the atomic mass scale, • 1 atomic mass unit (amu) has a mass equal to 1/12 of the mass of the carbon-12 atom. • a proton has a mass of about 1 (1.007) amu. • a neutron has a mass of about 1 (1.008) amu. • an electron has a very small mass, 0.000 549 amu. 51 Learning Check 52 Solution Identify each statement as describing a 1) proton, 2) neutron, or 3) electron. Identify each statement as describing a 1) proton, 2) neutron, or 3) electron. A. found outside the nucleus B. has a positive charge C. is neutral D. found in the nucleus A. 3 B. 1 C. 2 D. 1, 2 53 found outside the nucleus has a positive charge is neutral found in the nucleus 54 Chapter 3 Atoms and Elements Atomic Number 3.5 Atomic Number and Mass 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. • appears above the symbol of an element. Atomic Number Symbol 11 Na Copyright © 2009 by Pearson Education, Inc. 55 Atomic Number and Protons 56 Learning Check Examples of atomic number and number of protons: • Hydrogen has atomic number 1; every H atom has one proton. • Carbon has atomic number 6; every C atom has six protons. • Copper has atomic number 29; every Cu atom has 29 protons. • Gold has atomic number 79; every Au atom has 79 State the number of protons in each. A. A nitrogen atom 1) 5 protons 2) 7 protons 3) 14 protons B. A sulfur atom 1) 32 protons 2) 16 protons 3) 6 protons C. A barium atom 1) 137 protons 2) 81 protons 3) 56 protons protons. 57 Solution 58 Electrons in An Atom State the number of protons in each. A. A nitrogen atom 2) atomic number 7; 7 protons An atom • of an element is electrically neutral; the net charge of an atom is zero. • has an equal number of protons and electrons. number of protons = number of electrons B. A sulfur atom 2) atomic number 16; 16 protons Aluminum has 13 protons and 13 electrons. The net (overall) charge is zero. 13 protons (13+) + 13 electrons (13 -) = 0 C. A barium atom 3) atomic number 56; 56 protons 59 60 Mass Number Atomic Models The mass number • represents the number of particles in the nucleus. • is equal to the number of protons + the number of neutrons. 61 Learning Check 62 Solution An atom of zinc has a mass number of 65. A. How many protons are in this zinc atom? 1) 30 (atomic number 30) An atom of zinc has a mass number of 65. A. How many protons are in this zinc atom? 1) 30 2) 35 3) 65 B. How many neutrons are in the zinc atom? 2) 35 (65 – 30 = 35) B. How many neutrons are in the zinc atom? 1) 30 2) 35 3) 65 C. What is the mass number of a zinc atom that has 37 neutrons? 3) 67 (30 + 37 = 67) C. What is the mass number of a zinc atom that has 37 neutrons? 1) 37 2) 65 3) 67 63 Learning Check 64 Solution An atom has 14 protons and 20 neutrons. An atom has 14 protons and 20 neutrons. A. Its atomic number is 3) 34 A. It has atomic number 1) 14 2) 16 3) 34 B. It has a mass number of 3) 34 (14 + 20 = 34) 2) Ca 3) Se C. The element is 1) Si (Atomic number 14) 1) 14 2) 16 B. Its mass number is 1) 14 C. The element is 1) Si 65 66 Chapter 3 Atoms and Elements Isotopes 3.6 Isotopes and Atomic Mass Isotopes • are atoms of the same element that have different mass numbers. • have the same number of protons, but different numbers of neutrons. 24Mg 25Mg 26Mg 12 12 12 Copyright © 2009 by Pearson Education, Inc. 67 Atomic Symbol 68 Information from Atomic Symbols The atomic symbol for a specific atom of an element An atomic symbol gives the • represents a particular atom of an element. • gives the mass number in the upper left corner and • number of protons (p+), • number of neutrons (n), • and number of electrons (e-). the atomic number in the lower left corner. Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol: mass number 23 Na atomic number 11 69 Information from Atomic Symbols Learning Check Examples of number of subatomic particles for atoms Naturally occurring carbon consists of three isotopes: 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the following: Atomic symbol 16 8 31 O 8 p+ 8n 8 e- P 15 15 p+ 16 n 15 e- 70 65 Zn 12C 30 6 30 p+ 35 n 30 e- 71 13C 6 14C 6 protons ______ ______ ______ neutrons ______ ______ ______ electrons ______ ______ ______ 72 Solution Learning Check 12C 6 13C 14C 6 6 protons 6 p+ 6 p+ neutrons 6n 7n 8n electrons 6 e- 6 e- 6 e- Write the atomic symbols for atoms with the following subatomic particles: 6 p+ A. 8 p+, 8 n, 8 e- ___________ B. 17p+, 20n, 17e- ___________ C. 47p+, 60 n, 47 e- ___________ 73 Solution Learning Check A. 8 p+, 8 n, 8 e- 1. Which of the pairs are isotopes of the same element? 2. In which of the pairs do both atoms have 8 neutrons? 16O 8 B. 17p+, 74 20 n, 17e- 37Cl A. 17 C. 47p+, 60 n, 47 e- 15X 8 107Ag B. 47 C. 12X 15X 7 14X 6 6 15X 16X 7 8 75 Solution B. 12X 6 76 Isotopes of Magnesium 14X 6 The atomic symbols in “B.” represent isotopes of carbon with 6 protons each, but one has 6 neutrons and the other has 8. C. 15X 7 16X 8 These isotopes of nitrogen and oxygen have 8 neutrons. 77 78 Isotopes of Magnesium Isotopes of Sulfur A sample of naturally occurring sulfur contains several isotopes with the following abundances Isotope % abundance 32S 95.02 33S 0.75 34S 4.21 36S 0.02 32S, 33S, 34S, 36S 16 16 16 16 Copyright © 2009 by Pearson Education, Inc. 79 Isotopes of Some Elements and Their Atomic Mass Atomic Mass Most elements have two or more isotopes that contribute to the atomic mass of that element. The atomic mass of an element • is listed below the symbol of each element on the periodic table. • gives the mass of an “average” atom of 80 Na 22.99 each element compared to 12C. • is not the same as the mass number. 81 Atomic Mass for Cl 82 Learning Check The atomic mass of chlorine is Using the periodic table, specify the atomic mass of each element. • due to all the Cl isotopes. • not a whole number. • the average of two isotopes: 35Cl and 37Cl. 83 A. calcium __________ B. aluminum __________ C. lead __________ D. barium __________ E. iron __________ 84 Solution Calculating Atomic Mass Using the periodic table, specify the atomic mass of each element: A. calcium 40.08 amu B. aluminum 26.98 amu C. lead 207.2 amu D. barium 137.3 amu E. iron 55.85 amu The calculation for atomic mass requires the • percent(%) abundance of each isotope. • atomic mass of each isotope of that element. • sum of the weighted averages. mass of isotope(1)x (%) + mass of isotope(2) x (%) + 100 100 85 Calculating Atomic Mass for Cl 35Cl 86 Calculating Atomic Mass Mg Isotope Mass has atomic mass 34.97 amu (75.76%) and 37C Abundance has atomic mass 36.97 amu (24.24%). 24Mg = 23.99 amu x 78.70/100 = 18.88 amu • Use atomic mass and percent of each isotope to calculate the contribution of each isotope to the weighted average. = 26.49 amu 34.97 x 75.76 100 = 8.961 amu 36.97 x 24.24 100 25Mg = 24.99 amu x 10.13/100 = 2.531 amu 26Mg = 25.98 amu x 11.17/100 = • Sum is atomic mass of Cl Atomic mass (average mass) Mg 2.902 amu = 24.31 amu 35.45 amu 87 88 Learning Check Atomic Mass of Magnesium The atomic mass of Mg • is due to all the Mg isotopes. • is a weighted average. • is not a whole number. Gallium is an element found in lasers used in compact disc players. In a sample of gallium, there is 60.10% of 69Ga (atomic mass 68.926) atoms and 39.90% of 71Ga (atomic mass 70.925) atoms. What is the atomic mass of gallium? 89 90 Chapter 3 Atoms and Elements Solution 69Ga 68.926 amu x 60.10 100 3.7 Electron Energy Levels = 41.42 amu (from 69Ga) 71Ga 70.925 amu x 39.90 = 28.30 amu (from 71Ga) 100 31 Atomic mass Ga = 69.72 amu Ga 69.72 Copyright © 2009 by Pearson Education, Inc. 91 Energy Levels 92 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 93 Orbitals 94 Orbitals An orbital • is a three-dimensional space around a nucleus, where an electron is most likely to be found. An s orbital •has a spherical shape around the nucleus. •is found in each energy level. • has a shape that represents electron density (not a path the electron follows). A p orbital • has a two-lobed shape. • can hold up to 2 electrons. • is one of three p orbitals in each energy level from n = 2. 95 96 Electron Level Arrangement Orbitals In the electron level arrangement for the first 18 elements • electrons are placed in energy levels (1, 2, 3, etc.), beginning with the lowest energy level • there is a maximum number in each energy level. Energy level Number of electrons 1 2 (up to He) 2 8 (up to Ne) 3 8 (up to Ar) 4 2 (up to Ca) 97 Learning Check 98 Solution Write the electron level arrangement for each: Write the electron level arrangement for each: 1. N 1. N 2, 5 2. Cl 2. Cl 2, 8, 7 3. K 3. K 2, 8, 8, 1 99 Learning Check 100 Solution Identify the element with each electron level arrangement: Identify the element with each electron level arrangement: 1. 2, 2 1. Be 2, 2 2. 2, 8, 3 2. Al 2, 8, 3 3. 2, 7 3. F 2, 7 101 102 Chapter 3 Atoms and Elements 3.8 Periodic Trends Copyright © 2009 by Pearson Education, Inc. 104 Valence Electrons Groups and Valence Electrons The valence electrons • determine the chemical properties of the elements. • are the electrons in the highest energy level. • are related to the group number of the element. All the elements in a group have the same number of valence electrons. Example: Elements in group 2A (2) have two (2) valence electrons. Be 2, 2 Mg 2, 8, 2 Ca 2, 8, 8, 2 Sr 2, 8, 18, 8, 2 Example: Phosphorus has 5 valence electrons. 5 valence electrons P in Group 5A(15) 2, 8, 5 105 Periodic Table and Valence Electrons Representative Elements Group Numbers 1 2 3 4 5 6 7 H 1 Li 2,1 Be 2,2 B 2,3 C 2,4 N 2,5 Na Mg Al Si 2,8,1 2,8,2 2,8,3 2,8,4 P 2,8,5 O 2,6 S 2,8,6 F 2,7 106 Learning Check State the number of valence electrons for each. A. O 8 He 2 1) 4 2) 6 3) 8 2) 3 3) 1 2) 5 3) 7 B. Al Ne 2,8 1) 13 Cl Ar 2,8,7 2,8,8 107 C. Cl 1) 2 108 Solution Learning Check State the number of valence electrons for each. A. O State the number of valence electrons for each. A. calcium 1) 1 2) 2 3) 3 2) 6 B. Al 2) 3 C. Cl 3) 7 B. group 6A (16) 1) 2 2) 4 3) 6 C. tin 1) 2 2) 4 3) 14 109 Solution 110 Learning Check State the number of valence electrons for each. A. calcium 2) 2 For the element with the following electron arrangement: 1) State the number of valence electrons. 2) Identify the element. B. group 6A (16) 3) 6 A. 2, 8, 5 B. 2, 8, 8, 2 C. 2, 7 C. tin 2) 4 111 Solution 112 Electron-Dot Symbols An electron-dot symbol • shows the valence electrons around the symbol of the element. • for Mg has 2 valence electrons as single dots on the sides of the symbol Mg. . . ·Mg · or Mg · or ·Mg or ·Mg · For the element with the following electron arrangement 1) State the number of valence electrons 2) Identify the element. A. 2, 8, 5 1) 5 2) phosphorus B. 2, 8, 8, 2 1) 2 2) calcium C. 2, 7 1) 7 2) fluorine 113 114 Writing Electron-Dot Symbols Groups and Electron-Dot Symbols In a group, all the electron-dot symbols have the same number of valence electrons (dots). Electron-dot symbols for • groups 1A (1) to 4A (14) use single dots. · · Na · · Mg · · Al · ·C· · Example: Atoms of elements in Group 2A (2) each have 2 valence electrons. · Be · · Mg · · Ca · · Sr · · Ba · • groups 5A (15) to 7A (17) use pairs and single dots. ·· ·P· · ·· : O· · 115 Learning Check Solution A. . X is the electron-dot symbol for B. .. .X. . 1) Na 2) K A. 3) Al 2) N . X is the electron-dot symbol for 1) Na B. is the electron-dot symbol of 1) B 116 3) P 2) K .. .X . . is the electron-dot symbol of 2) N 3) P 117 Atomic Size 118 Atomic Radius Within A Group Atomic size is described Atomic radius increases going down each group of representative elements. using the atomic radius; the distance from the nucleus to the valence electrons. 119 120 Atomic Radius Across a Period Learning Check Going across a period from left to right, • an increase in the number of protons increases attraction for valence electrons. • atomic radius decreases. Select the element in each pair with the larger atomic radius. A. B. C. Li or K K or Br P or Cl Copyright © 2009 by Pearson Education, Inc. 121 Solution 122 Ionization Energy Select the element in each pair with the larger atomic radius. Ionization energy is the energy it takes to remove a valence electron. Na(g) + Energy (ionization) -> Na+(g) + e- A. K B. K C. P 123 Ionization Energy In a Group 124 Ionization Energy Going up a group of representative elements, • the distance decreases between nucleus and valence electrons. • Metals have • • the ionization energy increases. lower ionization energies. Nonmetals have higher ionization energies. Copyright © 2009 by Pearson Education, Inc. 125 126 Learning Check Solution Select the element in each pair with the higher ionization energy. Select the element in each pair with the higher ionization energy. A. B. C. A. B. C. Li or K K or Br P or Cl 127 Li Br Cl 128