GenChem_ch02_lecture_slides PDF

Atoms and the Periodic Table Chapter 2 Interactive General Chemistry, © 2019 Macmillan Learning Chapter Outline Section 2.1 Chemical Symbols Section 2.2 The Laws of Chemical Combination Section 2.3 The History of the Atom Section 2.4 Subatomic Particles, Isotopes, and Ions Sect...

Atoms and the Periodic Table Chapter 2 Interactive General Chemistry, © 2019 Macmillan Learning Chapter Outline Section 2.1 Chemical Symbols Section 2.2 The Laws of Chemical Combination Section 2.3 The History of the Atom Section 2.4 Subatomic Particles, Isotopes, and Ions Section 2.5 Atomic Masses Section 2.6 The Periodic Table 2 Interactive General Chemistry, © 2019 Macmillan Learning Section 2.1 Chemical Symbols Recognize the symbols for commonly used elements. Write the names of commonly used elements from their symbols. 3 Interactive General Chemistry, © 2019 Macmillan Learning Symbols for Elements Each chemical element is identified by an internationally recognized symbol consisting of one or two letters, such as C for carbon and He for helium. The first letter of an element’s symbol is always uppercase. If the symbol has a second letter, it is always lowercase. The symbols of some elements derive from their Latin names and are different from their English names. 4 Interactive General Chemistry, © 2019 Macmillan Learning Table 2.1 Elements Whose English Names and Symbols Begin with Different Letters English Basis for the English Basis for Symbol Symbol Name Symbol Name the Symbol Antimony Sb Stibium Potassium K Kalium Gold Au Aurum Silver Ag Argentum Iron Fe Ferrum Sodium Na Natrium Lead Pb Plumbum Tin Sn Stannum Mercury Hg Hydrargyrum Tungsten W Wolfram 5 Interactive General Chemistry, © 2019 Macmillan Learning Chemical Formulas Chemists write chemical symbols together in chemical formulas to identify compounds. CO is carbon monoxide while Co is cobalt. Chemical formulas give the relative number of each type of element in a compound. H2O has 2 atoms of H and 1 atom of O. When parentheses are present, multiply the number of each atom within the parentheses by the subscript outside the parentheses. Ca(NO3)2 has 1 Ca atom, 2 N atoms and 6 O atoms. 6 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.1 What are the names of the elements that correspond to the following symbols? a. C b. Br c. Hg d. Sr 7 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.1 Solution What are the names of the elements that correspond to the following symbols? a. C a. carbon b. Br b. bromine c. Hg c. mercury d. Sr d. strontium 8 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.2 Determine the relative number of each type of element in the following compounds. a. CO2 b. PCl3 c. Fe(OH)3 9 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.2 Solution Determine the relative number of each type of element in the following compounds. a. CO2 has two atoms of oxygen, O, for every atom of carbon, C. b. PCl3 has three atoms of chlorine, Cl, for every atom of phosphorus, P. c. Fe(OH)3 has three atoms of oxygen, O, and three atoms of hydrogen, H, for every atom of iron, Fe. 10 Interactive General Chemistry, © 2019 Macmillan Learning 2.1 Section Review The first letter in a symbol for an element is always capitalized; the second letter, if any, is lowercase. Not all element symbols start with the same letter as the English element name. Compounds are represented by the combination of chemical symbols in chemical formulas. Chemical formulas give the relative number of each type of element in a compound. 11 Interactive General Chemistry, © 2019 Macmillan Learning Section 2.6 The Periodic Table Discuss the contributions of Mendeleev and Meyer that led to the development of the periodic table. Classify the elements in a systematic manner based on their location in the periodic table. Identify periods, groups, and sections of the periodic table by name and number. 12 Interactive General Chemistry, © 2019 Macmillan Learning Development of the Periodic Table (1 of 2) Elements with similar chemical characteristics have been grouped together in various ways over time. The periodic table is the result of many years of refining this grouping. On the modern periodic table, elements are arranged horizontally in order of increasing atomic number and grouped vertically by similar properties. Initially, elements were ordered by atomic mass. After Dalton’s hypothesis was published, many scientists worked to determine relative atomic masses of the known elements. 13 Interactive General Chemistry, © 2019 Macmillan Learning Development of the Periodic Table (2 of 2) Two scientists, Dimitri Mendeleev and Lothar Meyer, combined the known atomic masses and the known elemental characteristics to produce a periodic table. However, Mendeleev used his periodic table to predict the existence and properties of yet-to-be discovered elements. Mendeleev chose to place the elements I and Te in opposite order than their atomic masses would suggest, placing them with elements of similar properties. His assumption, that their masses were incorrectly determined, proved to be correct. 14 Interactive General Chemistry, © 2019 Macmillan Learning Figure 2.15 Mendeleev’s Periodic Table 15 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.15 In the modern periodic table, locate two pairs of naturally occurring elements besides iodine and tellurium that are out of order, based on their atomic masses. 16 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.15 Solution In the modern periodic table, locate two pairs of naturally occurring elements besides iodine and tellurium that are out of order, based on their atomic masses. There are two other pairs of elements that are out of place according to atomic mass (but not when ordered by atomic number): argon and potassium cobalt and nickel 17 Interactive General Chemistry, © 2019 Macmillan Learning Noble Gases The noble gases are colorless, odorless, and mostly inert. These were not discovered until after the periodic table was first developed. 18 Interactive General Chemistry, © 2019 Macmillan Learning Using the Modern Periodic Table Elements within a horizontal row are in the same period. There are seven period in the periodic table, with the sixth and seventh periods including the inner transition elements. Elements within a vertical column are in the same group or family and have similar chemical properties. 19 Interactive General Chemistry, © 2019 Macmillan Learning Online Resource: Figure 2.16 - Periodic Table Figure 2.16 Periodic Table of the Elements 20 Interactive General Chemistry, © 2019 Macmillan Learning Group/Family Designations Older group numbering system uses Group 1–8 plus A or B designation. Modern group numbering system is simply 1–18 from left to right. Group names: Groups 1 and 2 are the alkali metals and alkaline earth metals. Group 11 contains the coinage metals. Group 17 and 18 are the halogens and the noble gases. 21 Interactive General Chemistry, © 2019 Macmillan Learning Figure 2.17 Group Names 22 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.16 Which element begins the fourth period of the periodic table? Which element ends it? How many elements are in that period? 23 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.16 Solution Which element begins the fourth period of the periodic table? Which element ends it? How many elements are in that period? Potassium begins period 4. Krypton ends period 4. There are 18 elements in period 4. 24 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.17 a. Select the period and group where each of the following elements is located: neon, Ne; rubidium, Rb; tungsten, W; and francium, Fr. b. Which of these elements have similar chemical properties? 25 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.17a Solution a. Select the period and group where each of the following elements is located: neon, Ne; rubidium, Rb; tungsten, W; and francium, Fr. Ne: period 2, group 18 Rb: period 2, group 1 W: period 6, group 6 Fr: period 7, group 1 26 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.17b Solution b. Which of these elements have similar chemical properties? Rb and Fr 27 Interactive General Chemistry, © 2019 Macmillan Learning Larger Groups on the Periodic Table The main group elements are those found in groups 1, 2, and 13– 18; are the more common elements; and have more predictable chemistry. The transition elements are those found in groups 3–12 and are metals. The inner transition elements are those typically displayed in the two rows beneath the main periodic table. Elements 58–71 are the lanthanoids and elements 90–103 are the actinoids. 28 Interactive General Chemistry, © 2019 Macmillan Learning Figure 2.18 Main Group Elements, Transition Elements, and Inner Transition Elements 29 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.18 Classify the following elements as main group elements, transition elements, or inner transition elements. a. Cs b. In c. U 30 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.18 Solution Classify the following elements as main group elements, transition elements, or inner transition elements. a. Cs: main group element b. In: main group element c. U: inner transition element (actinoid) 31 Interactive General Chemistry, © 2019 Macmillan Learning Metals, Nonmetals, and Metalloids Metals make up the majority of elements and are located on the left side of the periodic table. Metals have specific properties; they are shiny, malleable and ductile, and conductors of heat and electricity. Nonmetals consist of hydrogen plus the elements on the upper- right side of the table and are brittle as solids. Metalloids are the elements that border these two larger categories and share properties with both metals and nonmetals. 32 Interactive General Chemistry, © 2019 Macmillan Learning Figure 2.19 Metals, Nonmetals, and Metalloids 33 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.19 Which of the following elements are metals and which are nonmetals? a. calcium, Ca b. phosphorus, P c. nickel, Ni d. the carbon in a diamond, C 34 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.19 Solution Which of the following elements are metals and which are nonmetals? a. calcium, Ca: metal b. phosphorus, P: nonmetal c. nickel, Ni: metal d. the carbon in a diamond, C: nonmetal 35 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.20 Use the periodic table to identify each of the following. a. the fifth element in the first row of transition metals b. the element of the fourth period that is also in group 6 c. the seventh transition element d. the first element of group 8 e. the third halogen f. the first alkaline earth metal g. the first coinage metal 36 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.20 Solution Use the periodic table to identify each of the following. a. the fifth element in the first row of transition metals a. Mn b. the element of the fourth period that is also in group 6 b. Cr c. the seventh transition element c. Co d. the first element of group 8 d. Fe e. the third halogen e. Br f. the first alkaline earth metal f. Be g. the first coinage metal g. Cu 37 Interactive General Chemistry, © 2019 Macmillan Learning 2.6 Section Review The periodic table was originally developed using atomic masses and the chemical and physical properties of the elements, but it is now known that atomic numbers, not atomic masses, are the basis for the properties of an element. The modern periodic table is arranged in order of increasing atomic number. The organization of elements in the periodic table makes it easier to identify the similarities and differences among different elements. Elements in the same group in the periodic table generally have similar chemical properties. 38 Interactive General Chemistry, © 2019 Macmillan Learning  39 Interactive General Chemistry, © 2019 Macmillan Learning Section 2.2 The Laws of Chemical Combination Calculate some of the quantities involved in chemical combinations of elements using the classical laws known during John Dalton’s time. 40 Interactive General Chemistry, © 2019 Macmillan Learning The Law of Conservation of Mass During chemical reactions, matter is neither lost nor destroyed. This was not always obvious (e.g., the ashes left from a campfire have much less mass than the wood that was burned). Antoine Lavoisier carried out a quantitative experiment of the reaction of phosphorus with oxygen, showing that mass is conserved during a chemical reaction. (The reaction was initiated using sunlight and a magnifying glass.) This work led to other scientists to carry out experiments to confirm his conclusions. 41 Interactive General Chemistry, © 2019 Macmillan Learning Figure 2.1 An Experiment to Illustrate the Law of Conservation of Mass 42 Interactive General Chemistry, © 2019 Macmillan Learning Online Resource: Figure 2.2 - Conservation of Mass - Interactive Figure 2.2 Conservation of Mass Activity 43 Interactive General Chemistry, © 2019 Macmillan Learning Law of Definite Proportions The law of definite proportions states that any given compound is composed of definite proportions by mass of its elements. In all samples of pure water, the mass ratio of oxygen to hydrogen is 8:1. The proportion by mass of an element in a compound is the ratio of the mass of the element to the total mass of the compound. The percent by mass of the element in the compound is just the proportion of the element multiplied by 100%. 44 Interactive General Chemistry, © 2019 Macmillan Learning Proportion and Percent by Mass of the Elements in Sucrose, C12H22O11 144 g Carbon: 0.421 × 100% Carbon: = 0.421 342 g = 42.1% 22 g Hydrogen: 0.064 × 100% Hydrogen: = 0.064 342 g = 6.4% 176 g Oxygen: 0.515 × 100% Oxygen: = 0.515 342 g = 51.5% 45 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.3 a. A 4.33 g sample of dinitrogen monoxide, N2O, is composed of 63.65% nitrogen and 36.35% oxygen by mass. What is the percent composition of a 14.9 g sample of N2O? b. Nitrogen monoxide, NO, has a percent composition of 46.68% nitrogen and 53.32% oxygen by mass. What possible percentages of nitrogen could be in a mixture of N2O and NO? 46 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.3a Solution a. A 4.33 g sample of dinitrogen monoxide, N2O, is composed of 63.65% nitrogen and 36.35% oxygen by mass. What is the percent composition of a 14.9 g sample of N2O? All pure samples of N2O have the same percent composition: 63.65% nitrogen and 36.35% oxygen by mass. 47 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.3b Solution b. Nitrogen monoxide, NO, has a percent composition of 46.68% nitrogen and 53.32% oxygen by mass. What possible percentages of nitrogen could be in a mixture of N2O and NO? The percent by mass of nitrogen in the mixture must be between 46.68% and 63.65%. 48 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.4 Calculate the mass of nitrogen in a 4.75 g sample of nitrogen monoxide, NO, which has a percent composition of 46.68% nitrogen and 53.32% oxygen by mass. 49 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.4 Solution Calculate the mass of nitrogen in a 4.75 g sample of nitrogen monoxide, NO, which has a percent composition of 46.68% nitrogen and 53.32% oxygen by mass. Rearrange the equation for percent by mass to solve for the mass of the element. mass of element % by mass = × 100 % mass of sample % by mass mass of element = × mass of sample 100% 46.68% mass of N = 4.75 g = 2.22 g N 100% 50 Interactive General Chemistry, © 2019 Macmillan Learning The Law of Multiple Proportions The law of multiple proportions states that for any two (or more) compounds that are composed of the same elements, for a given mass of one of the elements, the ratio of the masses of any other element in the compounds is a small, whole-number ratio. For example, for every 1 g of C in CO, there are 1.33 g O and for every 1 g of C in CO2, there are 2.66 g of O. 2.66/1.33 = 2/1. 51 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.5 A sample of nitrogen monoxide, NO, consists of 14.01 g of nitrogen and 16.00 g of oxygen, whereas a sample of nitrogen dioxide, NO2, consists of 14.01 g of nitrogen and 32.00 g of oxygen. Show that NO and NO2 follow the law of multiple proportions. 52 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.5 Solution (1 of 2) A sample of nitrogen monoxide, NO, consists of 14.01 g of nitrogen and 16.00 g of oxygen, whereas a sample of nitrogen dioxide, NO2, consists of 14.01 g of nitrogen and 32.00 g of oxygen. Show that NO and NO2 follow the law of multiple proportions. Start by calculating the N:O ratio for both compounds. 14.01 g N For NO: = 0.8756 16.00 g O 14.01 g N For NO2: = 0.4378 32.00 g O 53 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.5 Solution (2 of 2) A sample of nitrogen monoxide, NO, consists of 14.01 g of nitrogen and 16.00 g of oxygen, whereas a sample of nitrogen dioxide, NO2, consists of 14.01 g of nitrogen and 32.00 g of oxygen. Show that NO and NO2 follow the law of multiple proportions. Now compare the two ratios by dividing the larger by the smaller. N: O ratio for NO 0.8756 = = 2.000 N: O ratio for NO2 0.4378 The ratio of N:O mass ratios for these compounds is a whole number, following the law of multiple proportions. 54 Interactive General Chemistry, © 2019 Macmillan Learning 2.2 Section Review Careful measurements of the masses of reactants and products in chemical reactions led to the development of the laws of conservation of mass, definite proportions, and multiple proportions. These three laws of chemical composition formed the basis for the theoretical development of chemistry. 55 Interactive General Chemistry, © 2019 Macmillan Learning Section 2.3 The History of the Atom Explain the classical laws of chemical combination using Dalton’s atomic theory. Outline the series of experiments that culminated in Rutherford’s nuclear model of the atom. 56 Interactive General Chemistry, © 2019 Macmillan Learning Dalton’s Atomic Theory (1 of 2) 1. Matter is made up of very tiny, indivisible particles called atoms. 2. Each atom of a particular element has the same mass, but the mass of an atom of one element is different from the mass of an atom of any other element. 57 Interactive General Chemistry, © 2019 Macmillan Learning Dalton’s Atomic Theory (2 of 2) 3. Atoms combine to form what we now call molecules. When they do so, they combine in small, whole- number ratios. 4. Atoms of some pairs of elements can combine with each other in different small, whole-number ratios to form different compounds. 58 Interactive General Chemistry, © 2019 Macmillan Learning Modern Revisions of Dalton’s Theory The discovery of subatomic particles and nuclear reactions corrected the notion that atoms are indivisible. Also, the discovery of isotopes disproved that all atoms of the same element have the same mass. 59 Interactive General Chemistry, © 2019 Macmillan Learning Dalton’s Theory and the Law of Conservation of Mass Atoms combine to form compounds. Atoms do not break down and are not built out of nothing. They merely exchange partners to form new compounds. Therefore, mass is conserved during a chemical reaction. 60 Interactive General Chemistry, © 2019 Macmillan Learning Dalton’s Theory and the Law of Definite Proportions Atoms combine to form compounds in small, whole-number ratios. Each compound contains atoms of specific elements in a very specific ratio. Thus, all samples of a pure compound have identical proportions by mass. 61 Interactive General Chemistry, © 2019 Macmillan Learning Dalton’s Theory and the Law of Multiple Proportions Atoms of some pairs of elements can combine with each other in different small, whole-number ratios to form different compounds. When atoms of the same two elements combine in different ratios to form different compounds, if the mass of one element is held constant, the ratio of the masses of the other element must be a whole-number ratio. 62 Interactive General Chemistry, © 2019 Macmillan Learning Discovery of the Electron (1897) (1 of 2) J. J. Thomson applied a strong electrical current to various substances in a device called a cathode-ray tube. The energy caused rays to be emitted, and the device allowed the rays to pass through a hole and strike a fluorescent screen at the far end of the tube. 63 Interactive General Chemistry, © 2019 Macmillan Learning Discovery of the Electron (1897) (2 of 2) The rays traveled from the negatively charged electrode to the positive electrode and could be deflected by an external magnetic field. Different substances emitted identical cathode rays with a charge-to-mass ratio of –1.76 × 108 C/g (C = coulomb, the SI unit of charge). Cathode rays are now known to be beams of electrons. 64 Interactive General Chemistry, © 2019 Macmillan Learning Figure 2.5 Cathode Ray Tube Evacuated glass Electron beam in tube Electrically- High voltage balanced electric charged plates and magnetic fields Magnet Electron beam in electric field only 65 Interactive General Chemistry, © 2019 Macmillan Learning Charge of an Electron The charge of a single electron was measured in 1909 by Robert Millikan in an experiment in which tiny drops of oil were sprayed into a chamber containing oppositely charged electrical plates. The chamber was then irradiated with X-rays to give the oil drops a negative charge. The lower, negative plate repelled the drops. By adjusting the magnitude of the electric field and watching to see exactly when a drop was suspended, he could determine the charge on an individual drop. After many measurements, he found that the total charge of the drops was a multiple of 1.60 × 10−19 C, which we now know is the charge of a single electron. 66 Interactive General Chemistry, © 2019 Macmillan Learning Online Resource: Figure 2.6 - Millikan Oil-Drop Experiment - Video Figure 2.6 Millikan’s Oil-Drop Experiment 67 Interactive General Chemistry, © 2019 Macmillan Learning Mass of an Electron Millikan used his charge of an electron and Thomson’s charge to mass ratio to determine the mass of an electron. mass mass = charge × charge −1.60 × 10−19 C 1 g −28 mass of an electron = 8 = 9.10 × 10 g −1.76 × 10 C 68 Interactive General Chemistry, © 2019 Macmillan Learning Figure 2.7 Dalton and Thompson’s Early Models of the Atom a. Dalton’s model of the atom b. Thomson’s plum-pudding model consisted of an indivisible consisted of negatively charged sphere. electrons suspended in a larger sphere of positive charge. 69 Interactive General Chemistry, © 2019 Macmillan Learning The Nuclear Model of the Atom (1 of 2) Radioactivity was discovered in 1896 by Henri Becquerel and further studied by Marie Curie in the early 1900s. They identified three types of radioactivity, positively charged alpha, α, particles; negatively charged beta, β, particles; and neutral gamma, γ, particles. In the early 1900s, Ernest Rutherford and students Geiger and Marsden tested the Thomson plum-pudding model of the atoms. 70 Interactive General Chemistry, © 2019 Macmillan Learning The Nuclear Model of the Atom (2 of 2) Plum-pudding model: negative electrons suspended within a positive sphere with evenly distributed mass. Alpha particles are small, positively charged particles traveling rapidly. Rutherford predicted that the alpha particles would pass through atoms without being stopped because there is no area of concentrated mass or concentrated charge to deflect them. He designed an experiment to test this hypothesis. 71 Interactive General Chemistry, © 2019 Macmillan Learning  Figure 2.8 Rutherford’s Gold Foil Experiment Some particles are deflected Most particles pass right through Atomic view of gold foil A few particles bounce back from the gold foil Thin gold foil Radioactive sample emits a beam of alpha particles Fluorescent screen 72 Interactive General Chemistry, © 2019 Macmillan Learning Rutherford’s Model 1. The atom’s positive charge and the majority of its mass are located in a relatively small area, which he later named the nucleus (plural nucleii). 2. The vast majority of the atom is empty space. Small, negatively charged electrons are spread throughout this empty space. 3. The number of negatively charged electrons is equal to the number of positively charged particles called protons inside the nucleus. 73 Interactive General Chemistry, © 2019 Macmillan Learning Further Conclusions and Discoveries The charge of the proton (+1) is equal in magnitude, but opposite in sign from the charge of the electron (–1). Electrically neutral atoms contain the same number of protons and electrons. Because helium has only one more proton than does hydrogen but four times the mass, Rutherford hypothesized the existence of another particle to account for this difference in mass. In 1932, James Chadwick demonstrated the presence of neutral particles in the nucleus, now called neutrons. 74 Interactive General Chemistry, © 2019 Macmillan Learning Figure 2.9 Model of the Atom 75 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.6 Dalton concluded that matter was made up of atoms. What additional insight about atoms did Thomson’s experiments reveal? 76 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.6 Solution Dalton concluded that matter was made up of atoms. What additional insight about atoms did Thomson’s experiments reveal? Thomson’s work showed that, upon addition of electrical energy, different substances release identical cathode rays that are negatively charged. Therefore, atoms are composed of smaller particles. 77 Interactive General Chemistry, © 2019 Macmillan Learning 2.3 Section Review Dalton’s atomic theory was an explanation for why the three laws of chemical combination (the law of conservation of mass, the law of definite proportions, and the law of multiple proportions) worked, and it provided the theoretical background for the entire future development of chemistry. Experiments demonstrated that the atom is not indivisible but consists of a nucleus made up of protons and neutrons that is surrounded by a cloud of electrons. The charges on protons and electrons are equal in magnitude, and atoms are electrically neutral, so atoms contain equal numbers of protons and electrons. 78 Interactive General Chemistry, © 2019 Macmillan Learning Section 2.4 Subatomic Particles, Isotopes, and Ions Identify the mass number of an atom using the number of each type of subatomic particle—protons, electrons, and neutrons—present in that atom, or vice versa. Identify which element an atom represents using the mass number of that atom, or vice versa. 79 Interactive General Chemistry, © 2019 Macmillan Learning Subatomic Particles and Isotopes Neutrons, protons, and electrons are called subatomic particles. The atomic nucleus is incredibly tiny, with a radius only 1/10,000 the radius of the cell. The nucleus contains almost all the mass of the atom. Electrons have very little mass, but occupy almost all the volume of the atom. 80 Interactive General Chemistry, © 2019 Macmillan Learning Table 2.2 Properties of Subatomic Particles † Location in the Particle Charge (e)* Mass (u) Atom Proton (p) +1 1.0073 In the nucleus Neutron (n) 0 1.0087 In the nucleus Electron (e) –1 0.000549 Outside the nucleus *The charges given are relative charges, based on the charge on the electron, e, as the fundamental unit of charge (1 e = –1.60 × 10–19 C). †The masses are given in atomic mass units, u. 81 Interactive General Chemistry, © 2019 Macmillan Learning Relative Sizes and Masses If an electron had the mass of a marble, a proton or neutron would have the mass of a bowling ball. If the entire nucleus were the size of a marble, the atom would be the size of a stadium. 82 Interactive General Chemistry, © 2019 Macmillan Learning Atomic Number, Z Atoms are electrically neutral because the number of protons, p, equals the number of electrons, e. number of p = number of e The atomic number, Z, is the number of protons in an atom’s nucleus. 𝑍=p The atomic number of every element is given as a whole number on the periodic table: 𝑍 = 1 is hydrogen and 𝑍 = 8 is oxygen. The atomic number is equal to the number of protons in the atom and determines its identity. 83 Interactive General Chemistry, © 2019 Macmillan Learning Isotopes of Elements The number of neutrons in the nuclei of atoms of the same element can differ. Two atoms with the same number of protons but different numbers of neutrons are isotopes of the same element. Isotopes have the same atomic number, but they have different masses because of the different numbers of neutrons. Each isotope of an element is usually identified by its mass number, A, which is the sum of the number of protons and the number of neutrons in the atom. 84 Interactive General Chemistry, © 2019 Macmillan Learning Mass Number: 𝐴 = p + n = 𝑍 + n The number of neutrons is the difference between the mass number and the atomic number. n = 𝐴– 𝑍 Symbols and names for isotopes include the element name or symbol and the mass number. The isotope of hydrogen with 1 proton and 0 neutrons is hydrogen-1, 1H. The isotope of hydrogen with 1 proton and 1 neutron is hydrogen-2, 2H. Atomic number can also be shown in isotope symbols. 85 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.7 How many protons, neutrons, and electrons are in a neutral atom of each of the following isotopes? a. S-32 b. 19F c. A neon atom with equal numbers of protons and neutrons in its nucleus 238 d. 92U 86 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.7 Solution How many protons, neutrons, and electrons are in a neutral atom of each of the following isotopes? a. S-32 a. 16 p, 16 e, 16 n b. 19F b. 9 p, 9 e, 10 n c. A neon atom with equal c. 10 p, 10 e, 10 n numbers of protons and neutrons in its nucleus d. 92 p, 92 e, 146 n 238 d. 92U 87 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.8 Assuming the element symbols are correct, which of the following isotopic symbols are correct? Explain why. 6 a. 14C b. O-17 c. 2H d. 14 6N e. S-6 88 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.8 Solution Assuming the element symbols are correct, which of the following isotopic symbols are correct? Explain why. a. 6 14C a. Incorrect. 𝑍 = 6 for C, which should be the subscript. b. O-17 b. Correct. c. 2H c. Incorrect. 𝑍 = 1 for H. d. 14 6N d. Incorrect. 𝑍 = 7 for N. e. S-6 e. Incorrect. 𝑍 = 16 for S, so the mass number must be greater than 16. 89 Interactive General Chemistry, © 2019 Macmillan Learning Ions Atoms can gain or lose electrons to form charged particles called ions. Sodium atoms can react to lose an electron, e–, forming a positively charged sodium cation: Na → Na+ + e− Oxygen atoms can react to gain electrons, forming a negatively charged oxide anion: O + 2e− → O2− 90 Interactive General Chemistry, © 2019 Macmillan Learning Online Resource: Figure 2.11 - Build an Atom - Interactive Figure 2.11 Build an Atom Activity 91 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.11 How many protons and electrons are in each of the following ions? a. F– b. Mg2+ c. N3– d. W6+ 92 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.11 Solution How many protons and electrons are in each of the following ions? a. F– a. 9 p and 10 e b. Mg2+ b. 12 p and 10 e c. N3– c. 7 p and 10 e d. W6+ d. 74 p and 68 e 93 Interactive General Chemistry, © 2019 Macmillan Learning 2.4 Section Review (1 of 2) Atoms are composed of subatomic particles: protons (p), neutrons (n), and electrons (e). Protons and neutrons are both found in the nucleus and account for essentially all of the mass of the atom; protons are positively charged, whereas neutrons are electrically neutral. The mass number, A, is the total number of protons and neutrons in the atom. Electrons are found outside the nucleus and make up essentially all of the volume of the atom; electrons are negatively charged. 94 Interactive General Chemistry, © 2019 Macmillan Learning 2.4 Section Review (2 of 2) The atomic number, Z, is equal to the number of protons in the nucleus and determines which element the atom is identified as. Atoms with different numbers of neutrons but the same number of protons are isotopes of each other. Ions are formed when an atom gains or loses electrons. Positively charged ions are called cations, whereas negatively charged ions are called anions. 95 Interactive General Chemistry, © 2019 Macmillan Learning Section 2.5 Atomic Masses Calculate the atomic mass of any element from the masses and abundances of its naturally occurring mixture of isotopes. 96 Interactive General Chemistry, © 2019 Macmillan Learning The Atomic Mass Scale Because atomic masses are so small, they are measured on a relative scale with one isotope assigned a value and all other measured relative to that isotope. Initially, this “standard” was oxygen, with the naturally occurring mixture of oxygen isotopes assigned a value of exactly 16 atomic mass units, u (sometimes abbreviated amu). In 1961, the mass of C-12 was designated as the new standard with C-12 atoms assigned a mass of exactly 12 u. 97 Interactive General Chemistry, © 2019 Macmillan Learning Modern Determination of Atomic Mass The atomic mass given on the periodic table is the weighted average of the actual masses of the naturally occurring isotope of that element. Weighted averages take into account the relative numbers of each type of isotope. 98 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.12 In a particular class, exams are worth 50% of the overall grade, quizzes are worth 25% of the overall grade, homework is worth 20% of the overall grade, and class participation is worth 5% of the overall grade. A particular student has earned an average score of 80.2% on the exams, 77.3% on the quizzes, 87.8% on the homework assignments, and 100.0% on class participation. What is this student’s overall grade in the course? 99 Interactive General Chemistry, © 2019 Macmillan Learning  Example 2.12 Solution In a particular class, exams are worth 50% of the overall grade, quizzes are worth 25% of the overall grade, homework is worth 20% of the overall grade, and class participation is worth 5% of the overall grade. A particular student has earned an average score of 80.2% on the exams, 77.3% on the quizzes, 87.8% on the homework assignments, and 100.0% on class participation. What is this student’s overall grade in the course? grade = 0.50(exam %) + 0.25(quiz %) + 0.20(homework %) + 0.05(participation %) grade = 0.50(80.2%) + 0.25(77.3%) + 0.20(87.8%) + 0.05(100%) grade = 40.10% + 19.33% + 17.56% + 5.00% = 82.0% 100 Interactive General Chemistry, © 2019 Macmillan Learning Calculation of Atomic Mass Elements often exist as a mixture of multiple isotopes that have different isotope masses. The atomic mass of an element is the weighted average of the masses of the naturally occurring isotopes atomic mass = ∑(fraction of isotope × mass of isotope) 101 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.13 Calculate the atomic mass of copper, given that naturally occurring copper consists of 69.17% 63Cu, which has an isotope mass of 62.9396 u, and 30.83% 65Cu, which has an isotope mass of 64.9278 u. 102 Interactive General Chemistry, © 2019 Macmillan Learning Example 2.13 Solution Calculate the atomic mass of copper, given that naturally occurring copper consists of 69.17% 63Cu, which has an isotope mass of 62.9396 u, and 30.83% 65Cu, which has an isotope mass of 64.9278 u. Convert the percentages to fractions and use the equation for a weighted average. atomic mass = ∑(fraction of isotope × mass of isotope) (0.6917)(62.9396 u) + (0.3083)(64.9278 u) = 63.55 u 103 Interactive General Chemistry, © 2019 Macmillan Learning Artificial Isotopes and Elements Artificial elements, which are all elements with 𝑍 > 92, do not have atomic masses. On the periodic table, the mass number of the most stable isotope of each artificial element is given in parentheses Artificial isotopes of naturally occurring elements do not contribute to the atomic mass. 104 Interactive General Chemistry, © 2019 Macmillan Learning 2.5 Section Review Historically, atomic mass was determined from mass ratios, such as those used to develop the law of definite proportions. Today, the mass and percent occurrence of each isotope are used. Atomic mass is the weighted average of the masses of the naturally occurring mixture of isotopes of an element. Do not confuse the atomic mass with the mass number, A, which is the total number of protons and neutrons in the atom. 105 Interactive General Chemistry, © 2019 Macmillan Learning