Chem Ch 2

1) In a chemical reaction, matter is neither created nor destroyed. Which law does this refer to? A) Law of Definite Proportions B) Law of the Conservation of Mass C) Law of Modern Atomic Theory D) Law of Multiple Proportions E) First Law of Thermodynamics

2) All samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements. Which law does this refer to? A) Law of Definite Proportions B) Law of the Conservation of Mass C) Law of Modern Atomic Theory D) Law of Multiple Proportions E) First Law of Thermodynamics

3) When two elements form two different compounds, the masses of element B that combine with 1 g of element A can be expressed as a ratio of small whole numbers. Which law does this refer to? A) Law of Definite Proportions B) Law of the Conservation of Mass C) Law of Modern Atomic Theory D) Law of Multiple Proportions E) First Law of Thermodynamics

4) Which of the following is an example of the law of multiple proportions? A) A sample of chlorine is found to contain three times as much Cl-35 as Cl-37. B) Two different compounds formed from carbon and oxygen have the following mass ratios: 1.33 g O: 1 g C and 2.66 g O: 1 g C. C) Two different samples of table salt are found to have the same ratio of sodium to chlorine. D) The atomic mass of bromine is found to be 79.90 amu. E) Nitrogen dioxide always has a mass ratio of 2.28 g O: 1 g N.

5) Which of the following statements is FALSE according to Dalton's Atomic Theory? A) Atoms combine in simple whole number ratios to form compounds. B) All atoms of chlorine have identical properties that distinguish them from other elements. C) One carbon atom will combine with one oxygen atom to form a molecule of carbon monoxide. D) Atoms of sodium do not change into another element during chemical reaction with chlorine. E) An atom of nitrogen can be broken down into smaller particles that will still have the unique properties of nitrogen.

6) Identify the equipment that Thomson utilized to do his research. A) cathode ray tube B) light bulb C) oscilloscope D) oil atomizer, light source, microscope E) electromagnetic field generator

7) Identify the equipment that Millikan utilized to do his research. A) cathode ray tube B) light bulb C) oscilloscope D) oil atomizer, light source, microscope E) electromagnetic field generator

8) Identify the description of an atom. A) neutrons and electrons in nucleus; protons in orbitals B) neutrons in nucleus; protons and electrons in orbitals C) protons and neutrons in nucleus; electrons in orbitals D) protons and electrons in nucleus; neutrons in orbitals E) electrons in nucleus; protons and neutrons in orbitals

9) Identify the largest subatomic particle. A) a neutron B) an electron C) a proton D) an orbital E) a nucleus

10) Identify the smallest subatomic particle. A) a neutron B) an electron C) a proton D) an alpha particle E) a nucleus

11) The mass number is equal to A) the sum of the number of the electrons and protons. B) the sum of the number of the neutrons and electrons. C) the sum of the number of protons, neutrons, and electrons. D) the sum of the number of protons and neutrons.

12) The atomic number is equal to A) the number of the protons. B) the sum of the number of the neutrons and electrons. C) the sum of the number of protons, neutrons, and electrons. D) the sum of the number of protons and neutrons.

13) What does "X" represent in the following symbol? 80 X 35 A) mercury B) chlorine C) scandium D) bromine E) selenium

14) What does "X" represent in the following symbol? 28 X 14 A) silicon B) sulfur C) zinc D) ruthenium E) nickel

15) Determine the number of protons, neutrons, and electrons in the following: 40 X 18 A) p+ = 18 n° = 18 e- = 22 B) p+ = 18 n° = 22 e- = 18 C) p+ = 22 n° = 18 e- = 18 D) p+ = 18 n° = 22 e- = 40 E) p+ = 40 n = 22 e- = 18

16) Determine the number of protons, neutrons, and electrons in the following: 25 X 12 A) p+ = 12 n° = 25 e- = 12 B) p+ = 12 n° = 12 e- = 13 C) p+ = 12 n° = 13 e- = 12 D) p+ = 25 n° = 12 e- = 13 E) p+ = 12 n° = 13 e- = 25

17) Determine the number of protons, neutrons, and electrons in the following: 65 X 29 A) p+ = 36 n° = 29 e- = 36 B) p+ = 29 n° = 29 e- = 36 C) p+ = 36 n° = 36 e- = 29 D) p+ = 29 n° = 36 e- = 29 E) p+ = 29 n° = 36 e- = 36

18) What element is defined by the following information? p+ = 11 n° = 12 e- = 11 A) sodium B) vanadium C) magnesium D) titanium E) selenium

19) What element is defined by the following information? p+ = 20 n° = 20 e- = 20 A) zirconium B) calcium C) potassium D) neon E) argon

20) What element is defined by the following information? p+ = 17 n° = 20 e- = 17 A) calcium B) rubidium C) chlorine D) neon E) oxygen

21) Which of the following statements about subatomic particles is TRUE? A) A neutral atom contains the same number of protons and electrons. B) Protons have about the same mass as electrons. C) Electrons make up most of the mass of an atom. D) Protons and neutrons have opposite, but equal in magnitude, charges. E) Neutrons and electrons are found in the nucleus of an atom.

22) Which of the following statements about isotopes is TRUE? A) Isotopes of the same element differ only in the number of electrons they contain. B) An isotope of an atom with a larger number of neutrons is larger than an isotope of the same atom that contains fewer neutrons. C) Isotopes of the same element have the same mass. D) Isotopes of the same element don't usually have the same properties. E) Some elements have 3 or more naturally occurring isotopes.

23) Give the symbol for silver. A) S B) Si C) Ar D) Ag E) Sl

24) Ions differ in the number of A) electrons. B) neutrons. C) protons. D) neutrons and protons. E) electrons and protons.

25) What species is represented by the following information? p+ = 12 n° = 14 e- = 10 A) Si4+ B) Mg C) Ne D) Si E) Mg2+

26) What species is represented by the following information? p+ = 47 n° = 62 e- = 46 A) Ag+ B) Nd C) Pd D) Ag E) Pd+

27) What species is represented by the following information? p+ = 17 n° = 18 e- = 18 A) Cl B) Cl- C) Ar D) Ar+ E) Kr

28) Identify the largest atom or ion of carbon. A) p+ = 6 n° = 6 e- = 6 B) p+ = 6 n° = 7 e- = 6 C) p+ = 6 n° = 6 e- = 7 D) p+ = 6 n° = 6 e- = 5

29) Predict the charge that an aluminum ion would have. A) 5- B) 1+ C) 1- D) 2+ E) 3+

30) Predict the charge that an ion formed from nitrogen would have. A) 1- B) 6+ C) 3- D) 3+ E) 2-

31) Which of the following statements is FALSE? A) Halogens are very reactive elements. B) The alkali metals are fairly unreactive. C) Sulfur is a main group element. D) Noble gases do not usually form ions. E) Zn is a transition metal.

32) Which of the following does NOT describe a metal? A) good conductor of heat B) good conductor of electricity C) tends to gain electrons D) forms ionic compounds with nonmetals E) found on the left side of the periodic table

33) Which of the following does NOT describe a nonmetal? A) tends to gain electrons B) found in the upper right hand corner of the periodic table C) poor conductor of electricity D) nonmetals are generally unreactive E) poor conductor of heat

34) Semiconductors are A) metalloids. B) noble gases. C) nonmetals. D) metals.

35) Which of the following statements is FALSE? A) Anions are usually larger than their corresponding atom. B) Metals tend to form cations. C) Atoms are usually larger than their corresponding cation. D) The halogens tend to form 1+ ions. E) Nonmetals tend to gain electrons.

36) Identify the green-yellowish gas that is used as a disinfecting agent. A) chlorine B) bromine C) iodine D) fluorine

37) Identify the instrument that is used to determine the mass of a molecule. A) mass spectrometer B) nuclear magnetic resonance spectrometer C) infrared spectrometer D) gas chromatograph E) ultraviolet spectrophotometer

38) The atomic mass for cadmium is A) 48 B) 112.41 C) 40.08 D) 20 E) 64.411

39) Calculate the atomic mass of silver if silver has 2 naturally occurring isotopes with the following masses and natural abundances: Ag-107 106.90509 amu 51.84% Ag-109 108.90476 amu 48.46% A) 107.90 amu B) 108.00 amu C) 107.79 amu D) 108.32 amu E) 108.19 amu

40) Calculate the atomic mass of gallium if gallium has 2 naturally occurring isotopes with the following masses and natural abundances: Ga-69 68.9256 amu 60.11% Ga-71 70.9247 amu 39.89% A) 69.72 amu B) 69.93 amu C) 70.00 amu D) 69.80 amu E) 70.68 amu

41) Silver has an atomic mass of 107.868 amu. The Ag-109 isotope (108.905 amu) is 48.16%. What is the amu of the other isotope? A) 106.905 amu B) 106.908 amu C) 106.903 amu D) 106.911 amu

42) Gallium has an atomic mass of 69.723 amu. The Ga-69 (68.926 amu) is 60.11%. What is the amu of the other isotope? A) 70.924 amu B) 70.928 amu C) 70.932 amu D) 70.920 amu

43) Calculate the atomic mass of element "X", if it has 2 naturally occurring isotopes with the following masses and natural abundances: X-45 44.8776 amu 32.88% X-47 46.9443 amu 67.12% A) 46.26 amu B) 45.91 amu C) 46.34 amu D) 46.84 amu E) 44.99 amu

44) Identify how the atomic mass of an element is determined. A) average of ions B) average of isotopic masses C) average of radioactive particles D) average of crude weights E) average of protons

45) What mass (in mg) does 2.63 moles of nickel have? A) 44.8 mg B) 2.23 × 10^4 mg C) 129 mg D) 3.56 × 10^5 mg E) 1.54 × 10^5 mg

46) How many moles of Kr are contained in 398 mg of Kr? A) 4.75 × 10^-3 moles Kr B) 33.4 moles Kr C) 2.11 × 10^-4 moles Kr D) 2.99 × 10^-3 moles Kr E) 1.19 × 10^-4 moles Kr

47) How many moles of Cs are contained in 595 kg of Cs? A) 2.23 × 10^2 moles Cs B) 4.48 × 10^3 moles Cs C) 7.91 × 10^4 moles Cs D) 1.26 × 10^3 moles Cs E) 5.39 × 10^2 moles Cs

48) How many iron atoms are contained in 354 g of iron? A) 2.62 × 10^25 Fe atoms B) 2.13 × 10^26 Fe atoms C) 4.69 × 10^24 Fe atoms D) 3.82 × 10^24 Fe atoms E) 9.50 × 10^22 Fe atoms

49) How many phosphorus atoms are contained in 158 kg of phosphorus? A) 3.07 × 10^27 phosphorus atoms B) 2.95 × 10^27 phosphorus atoms C) 3.25 × 10^28 phosphorus atoms D) 1.18 × 10^24 phosphorus atoms E) 8.47 × 10^24 phosphorus atoms

50) Calculate the mass (in kg) of 4.87 × 10^25 atoms of Zn. A) 5.29 kg B) 1.89 kg C) 8.09 kg D) 1.24 kg E) 1.09 kg

51) Calculate the mass (in ng) of 2.33 × 10^20 atoms of oxygen. A) 6.19 × 10^6 ng B) 1.62 × 10^7 ng C) 2.25 × 10^3 ng D) 3.73 × 10^6 ng E) 4.69 × 10^7 ng

52) How many xenon atoms are contained in 2.36 moles of xenon? A) 3.92 × 10^24 xenon atoms B) 2.55 × 10^23 xenon atoms C) 1.42 × 10^24 xenon atoms D) 7.91 × 10^25 xenon atoms E) 1.87 × 10^26 xenon atoms

1) Identify the discovery that Millikan made. A) the mass of a proton B) the charge of a proton C) the charge of a single electron D) the mass of a beta particle E) molecules

2) Identify the discovery that Thomson made. A) a neutron B) an electron C) the charge of a single electron D) an alpha particle E) anions

3) Identify the radioactive particle. A) a beta particle B) an anion C) a molecule D) an electron E) a mole

4) Rutherford proposed the A) atomic bomb. B) hydroelectric. C) First Law of Conservation. D) theory of explosives. E) nuclear theory.

5) Identify the charges of the protons, neutrons, and electrons. A) protons +1, neutrons 0, electrons -1 B) protons 0, neutrons -1, electrons 0 C) protons -1, neutrons -1, electrons 0 D) protons 0, neutrons 0, electrons 0 E) protons +1, neutrons +1, electrons +1

6) Identify the element that has an atomic number of 40. A) neon B) calcium C) zirconium D) bromine E) gold

7) Give the symbol for potassium. A) K B) P C) Po D) Ka E) Pt

8) An atom of 13C contains ________ protons. A) 6 B) 19 C) 7 D) 9 E) 13

9) An atom of 25Mg contains ________ electrons. A) 25 B) 37 C) 13 D) 23 E) 12

10) The atomic number of an atom of 130Xe is A) 184. B) 54. C) 76. D) 122. E) 130.

11) How many electrons are in each neutral atom of magnesium? A) 12 B) 13 C) 14 D) 12.3 E) 24.3

12) How many neutrons are in manganese-54? A) 25 B) 30 C) 29 D) 29.4 E) 54.9

13) How many protons are in nickel? A) 28 B) 30 C) 31 D) 30.7 E) 58.7

14) An ion has 26 protons, 29 neutrons, and 23 electrons. The symbol for the ion is ________. A) 55Fe3+ B) 55Fe3- C) 52Cu3+ D) 52Cu3- E) 55V3-

15) Isotopes differ in the number of A) gamma particles. B) electrons. C) compounds. D) neutrons. E) neutrons and protons.

16) Identify a cation. A) an atom that has lost an electron B) an atom that has gained an electron C) an atom that has lost a proton D) an atom that has gained a neutron

17) Identify an anion. A) an atom that has lost an electron B) an atom that has gained an electron C) an atom that has lost a proton D) an atom that has gained a neutron and a proton

18) How many electrons does the Se2- ion possess? A) 32 B) 36 C) 4 D) 0 E) 34

19) How many protons does the As3- ion possess? A) 30 B) 36 C) 4 D) 8 E) 33

20) What is the chemical symbol for thallium? A) Ti B) Tl C) Tm D) Th E) Tr

21) What is the chemical symbol for molybdenum? A) Ma B) Au C) Mo D) K E) Mb

22) What is the chemical symbol for carbon? A) Co B) Cr C) C D) Ca E) Cb

23) Which element has the chemical symbol, Rn? A) radium B) radon C) rhenium D) rhodium

24) Which element has the chemical symbol, Sn? A) samarium B) lead C) tin D) tungsten E) selenium

25) An atom that has an atomic number of 38 and a mass number of 88 is an isotope of an atom that has A) an atomic number of 39 and a mass number of 88. B) an atomic number of 38 and a mass number of 86. C) 50 neutrons and 38 protons. D) 50 protons and 38 neutrons.

26) Which of the following represent isotopes? A: 79 X B: 79 X C: 78 X D: 81 X 34 35 34 36 A) A and D B) A and C C) B and D D) C and D E) all of the above

27) What does "X" represent in the following symbol? 65 X 29 A) dysprosium B) nickel C) terbium D) silicon E) copper

28) How many protons (p) and neutrons (n) are in an atom of 227 Ac ? 89 A) 89 p, 138 n B) 89 p, 227 n C) 138 p, 89 n D) 227 p, 89 n

29) How many protons (p) and neutrons (n) are in an atom of calcium-46? A) 20 p, 26 n B) 20 p, 46 n C) 26 p, 20 n D) 46 p, 20 n

30) What is the element symbol for an atom that has 29 protons and 36 neutrons? A) Cu B) Kr C) N D) Tb

31) How many electrons are in a neutral atom of chlorine-37? A) 1 B) 17 C) 18 D) 37

32) Identify the chemical symbol of element Q in 18 Q. 8 A) Ar B) F C) Ne D) O

33) An atom of 131 I contains ________ neutrons. A) 53 B) 184 C) 78 D) 124 E) 131

34) The mass number of an atom of 79Br is ________. A) 35 B) 114 C) 44 D) 79 E) 72

35) What is the identity of element Q if the ion Q2+ contains 36 electrons? A) Ge B) Se C) Kr D) Sr

36) Give the number of neutrons in 31P3-. A) 18 B) 12 C) 19 D) 15 E) 16

37) Give the number of electrons in K+. A) 36 B) 80 C) 35 D) 45 E) 48

38) Give the number of protons in P3-. A) 18 B) 12 C) 19 D) 15 E) 16

39) How many electrons are in the ion, Ni2+? A) 26 B) 28 C) 30 D) 59 E) 52

40) How many electrons are in the ion, S2-? A) 14 B) 18 C) 30 D) 34 E) 23

41) In which of the following sets do all species have the same number of electrons? A) Cl-, Ar, Ca2+ B) C, N3-, O2- C) K+, Rb+, Cs+ D) Br, Br-, Br+

42) In which of the following sets do all species have the same number of protons? A) F-, Ne, Mg2+ B) C, N3-, O2- C) Sr2+, Ba2+, Ra2+ D) S, S2-, S2+

43) Predict the charge that a strontium ion would have. A) 6- B) 2- C) 4- D) 2+ E) 1+

44) Predict the charge that an ion formed from tellerium would have. A) 1- B) 6- C) 3- D) 4- E) 2-

45) Predict the charge that the ion formed from chlorine would have. A) 1- B) 2+ C) 1+ D) 4- E) 3-

46) Predict the charge of the most stable ion of sodium. A) 1+ B) 3- C) 4+ D) 5+ E) 6+

47) Which of the following elements is a metal? A) Sb B) O C) Br D) Ag E) He

48) Which of the following elements is a metalloid? A) As B) O C) I D) Co E) Xe

49) Which of the following elements is a noble gas? A) As B) C C) F D) Co E) He

50) Which of the following elements is a halogen? A) Po B) S C) I D) Sn E) Kr

51) Which of the following elements is a nonmetal? A) Pu B) C C) Br D) K E) Be

52) Which of the following elements is a alkali metal? A) U B) C C) F D) K E) Ca

53) Which of the following elements is an alkaline earth metal? A) La B) P C) I D) Rb E) Ba

54) Which of the following elements is a transition metal? A) Tc B) P C) F D) Cs E) Ca

55) Sodium belongs to the ________ group of the periodic table. A) alkali metal B) transition element C) noble gas D) nonmetal

56) Iodine belongs to the ________ group of the periodic table. A) alkali metal B) metal C) halogen D) noble gas

57) Helium belongs to the ________ group of the periodic table. A) alkali metal B) metal C) transition metal D) noble gas

58) Beryllium belongs to the ________ group of the periodic table. A) alkali metal B) alkaline earth metal C) transition element D) nonmetal

59) Which of the following elements has chemical properties similar to tellurium? A) bromine B) lithium C) nitrogen D) sulfur E) helium

60) Which of the following elements is a gas at room temperature? A) oxygen B) boron C) bromine D) sodium E) barium

61) Which of the following elements is a liquid at room temperature? A) radon B) boron C) mercury D) lithium E) calcium

62) Which of the following elements is a solid at room temperature? A) chlorine B) helium C) mercury D) oxygen E) barium

63) Which of the following elements is NOT a solid at room temperature? A) Mn B) Cr C) Hg D) Mg E) Na

64) Which of the following elements is classified as a metalloid? A) sodium B) germanium C) iodine D) gold E) calcium

65) Which of the following elements is a good conductor of heat and electricity? A) carbon B) chlorine C) xenon D) aluminum

66) Which one of the following elements is a poor conductor of heat and electricity? A) chromium B) iodine C) copper D) aluminum E) nickel

67) All of the following elements are nonmetals EXCEPT A) barium. B) nitrogen. C) oxygen.. D) argon. E) flourine.

68) Identify the cation. A) O2- B) Sr2+ C) Br D) Kr E) I2

69) Identify the anion. A) Te2- B) Ba2+ C) I D) Ne E) F2

70) Which of the following elements is NOT a metal? A) Mg B) Na C) He D) Au E) Mn

71) Which of the following elements is in Group 4? A) Hf B) Ca C) Bi D) Ne E) Cd

72) Which of the following elements is in Period 4? A) Zr B) Ca C) Bi D) He E) Ag

73) List the element that is in the highest percentage by mass in our bodies. A) nitrogen B) phosphorus C) oxygen D) silicon E) sodium

74) The average atomic mass for silver is ________. A) 28.09 B) 14 C) 107.87 D) 47

75) The atomic number for iron is ________. A) 192.22 B) 77 C) 55.85 D) 26

76) Which of the following contains the most atoms? You shouldn't need to do a calculation here. A) 10.0 g Mg B) 10.0 g Li C) 10.0 g Ca D) 10.0 g Kr E) 10.0 g Ba

77) Which of the following contains the fewest atoms? You shouldn't need to do a calculation here. A) 10.0 g Mg B) 10.0 g Li C) 10.0 g Ar D) 10.0 g Rb E) 10.0 g Cs

78) How many Li atoms are contained in 97.9 g of Li? A) 5.90 × 1025 Li atoms B) 7.09 × 1021 Li atoms C) 8.49 × 1024 Li atoms D) 4.27 × 1022 Li atoms E) 4.18 × 1024 Li atoms

79) Calculate the mass (in g) of 2.1 × 1024 atoms of W. A) 3.9 × 102 g B) 2.4 × 102 g C) 3.2 × 102 g D) 1.5 × 102 g E) 6.4 × 102 g

80) How many gold atoms are contained in 3.75 moles of gold? A) 1.23 × 10^24 gold atoms B) 2.26 × 10^24 gold atoms C) 2.26 × 10^23 gold atoms D) 9.03 × 10^25 gold atoms E) 6.50 × 10^25 gold atoms

81) What mass (in g) does 0.990 moles of Kr have? A) 83.5 g B) 119 g C) 52.8 g D) 60.0 g E) 35.6 g

82) How many moles of potassium are contained in 200 g of potassium? A) 5.11 moles B) 0.956 moles C) 13.3 moles D) 10.53 moles E) 6.46 moles

83) How many moles are in 2.16 × 10^24 atoms of magnesium? A) 35.9 moles B) 3.59 moles C) 0.359 moles D) 7.18 moles E) 0.90 moles

84) How many atoms are in 7.50 moles of Ca? A) 4.52 × 10^24 atoms B) 1.52 × 10^24 atoms C) 5.02 × 10^23 atoms D) 3.01 × 10^24 atoms E) 7.53 × 10^23 atoms

85) How many atoms are in 2.50 moles of N? A) 4.52 × 10^24 atoms B) 1.51 × 10^24 atoms C) 5.02 × 10^23 atoms D) 3.01 × 10^24 atoms E) 7.53 × 10^23 atoms

86) How many atoms of carbon are in 4.00 moles of C? A) 7.22 × 10^24 atoms B) 2.41 × 10^24 atoms C) 8.00 × 10^23 atoms D) 3.01 × 10^24 atoms E) 6.50 × 10^23 atoms

87) How many atoms are in 5.00 moles of O? A) 4.52 × 10^23 atoms B) 1.51 × 10^24atoms C) 5.02 × 10^23atoms D) 3.01 × 10^24 atoms E) 3.01 × 10^23 atoms

88) What mass (in kg) does 4.41 moles of copper have? A) 0.352 kg B) 0.122 kg C) 0.820 kg D) 0.280 kg E) 0.632 kg

89) Which of the following does NOT contain the same number of atoms as 3.30 moles of K? A) 3.30 moles of K B) 1.50 moles of Hf C) 3.30 moles of Os D) 3.30 moles of Co E) 3.30 moles of Au

90) Which of the following is equal to exactly 1 mole of atoms? A) 6.00 grams of carbon B) 30.69 grams of nickel C) 12.01 grams of carbon D) 12.31 grams of magnesium E) 34.00 grams of selenium

91) Which of the following is equal to exactly Avogadro's number of atoms? A) 8.00 grams of oxygen B) 35.38 grams of zinc C) 12.01 grams of carbon D) 11.99 grams of sodium E) 34.00 grams of selenium

92) How many argon atoms are contained in 7.66 ×10^5 mmol of argon? A) 4.61 × 10^26 Ar atoms B) 4.61 × 10^29 Ar atoms C) 3.83 × 10^26 Ar atoms D) 7.86 × 10^21 Ar atoms E) 3.24 × 10^26 Ar atoms

1) magnesium 2) carbon 3) potassium 4) iron 5) silicon

Describe an atom and what it is made up of according to modern atomic theory.

The atomic number is equal to the number of ________.

Why do the isotopes of the same element have the same atomic size?

Why doesn't a mass spectrum of silver have a peak at 107.9 amu?

Are anions typically larger or smaller than their corresponding atom? Why?

Give the name of the element whose symbol is Na.

Describe the difference between ions and isotopes.

Give an example of an halogen.

What group of elements in the periodic table are the most unreactive and why?

Why do elements in the same group tend to have similar chemical properties?

Give the name of the instrument that is used to measure masses of atoms and the percent abundance of isotopes.

The number 6.022 × 10^23 is called ________.