Ch.2 - Atoms & ElementsWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Isotopes represent atoms of an element that contain the same atomic number (same number of protons), but different mass numbers (different number of neutrons). 

Atomic Mass

The atomic mass of an element that you find on the periodic table represents the average masses of its isotopes. 

Recall that the mass number or atomic mass of an element represents the total number of its protons and neutrons, while the atomic number represents the total number of its protons. 

Concept #1: The atomic masses listed for the elements on the periodic table are the average masses of their isotopes. 

Isotopes are elements with the same number of protons, but different number of neutrons.

Concept #2: Calculating the average mass of an element

Example #1: Antimony has two common isotopes. If one of the isotopes 121Sb has an isotopic mass of 120.9038 amu and a natural abundance of 57.25%, what is the isotopic mass (to 4 significant figures) of the other isotope? The atomic mass of antimony is 121.8 g/mol. 

Example #2: The atomic mass of an imaginary element A is 251.7 amu. If element A consists of two isotopes that have atomic masses of 250 and 253 respectively, what is the natural abundance of each isotope?

A lesser known term referred to as isotones involves atoms that have the same number of neutrons, but different number of protons

Additional Problems
Naturally occurring bromine consists of two isotopes, 79Br and 81Br with isotopic masses of 78.9183 and 80.9163, respectively. Given that the observed atomic mass of bromine is 79.904, calculate the percent abundance of 79Br and 81Br in naturally occurring bromine. 
The element antimony has an atomic weight of 121.757 amu and only two naturally occurring isotopes. One isotope has an abundance of 57.30% and an isotopic mass of 120.904. Based on these data, what is the mass of the second isotope?
Gallium is a metal with a wide variety of uses (e.g., light-emitting diodes, lasers, medical imaging). Fill in the missing isotopic data on gallium in the table.
Assume that potassium (atomic mass = 39.10) has only two isotopes, one of which is potassium-39 (isotopic mass = 38.9637 amu, abundance = 93.258%). What is the mass of the second isotope? A. 43.06 amu B. 40.95 amu C. 42.05 amu D. 39.97 amu E. 41.88 amu
An unknown element E is found to have two isotopes. The atomic mass of E is 57.15 amu. The mass of the first isotope E - 56 is 56.482 amu, and its natural abundance is 69.19%. Calculate the mass of the second isotope of E? a. 68.38 amu b. 54.98 amu c. 58.65 amu d. 57.82 amu e. 56.82 amu
Consider the following three pairs of species: I. 55Fe3+ and 56Fe2+ II. Na+ and Ne III. 13C and 14C Which of the following statements is  NOT true?   A) I and III both contain pairs of isotopes. B) II shows two species with different number of electrons. C) III shows two species with different mass numbers, but the same atomic numbers. D) I shows two species with the same number of protons.
Which of the following symbols represent isotopes of nitrogen? a. i only b. ii only c. iii only d. i and ii e. i and iii
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
An element has three isotopes. Given the abundances and relative masses, calculate the average atomic mass and determine (from the periodic table) which element it is.      
Rubidium (Rb) has only two naturally occurring isotopes. The first isotope has a mass of exactly 86.909 amu and the second isotope has a percent abundance of 72.17%. What is the mass of the second isotope in amu? a. 83.99 g/mol b. 84.91 g/mol c. 85.49 g/mol d. 85.49 g/mol e. 84.91 g/mol
Fill in the blank spaces and write out all the symbols in the left hand column in full, in the form AZX  (i.e., include the appropriate values of Z and A as well as the correct symbol X).  
Calculate the atomic mass of element ʺXʺ, 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) 46.27 amu B) 45.91 amu C) 46.34 amu D) 46.84 amu E) 44.99 amu
Write isotopic symbols of the form AzX  for each isotope.  a. The copper isotope with 34 neutrons
Write isotopic symbols of the form AzX  for each isotope.  b. The copper isotope with 36 neutrons 
Write isotopic symbols of the form AzX  for each isotope.  c. the potassium isotope with 21 neutrons 
Write isotopic symbols of the form AzX  for each isotope.  d. the argon isotope with 22 neutrons
An unknown element, X, has three naturally occurring isotopes. The masses of the three isotopes are 54.335, 59.345 and 62.349 The two have a percent abundance of 35.528% and 38.136% respectively. What is the average mass of the element? a. 58.676 b. 65.713 c. 58.481 d. 58.356 e. 58.873
Complete the following table.
Iron has four stable isotopes; their masses and natural abundances are listed in the table.  Calculate the average atomic mass of iron, in amu. 
Naturally occuring iodine has an atomic mass of 126.9045. A 12.3849-g sample of iodine is accidentally contaminated with an additional 1.00070 g of 129l, a synthetic radioisotope of iodine used in the treatment of certain diseases of the thyroid gland. The mass of 129l, is 128.9050 amu. Find the apparent "atomic mass" of the contaminated iodine.
Nuclei with the same number of  neutrons but different mass numbers are called isotones. Write the symbols of four isotones of  236Th.
Boron and Fluorine.  Give the number of protons and neutrons in the following isotopes: 1. boron-10         _____ protons      _____neutrons 2. boron-11         _____ protons      _____neutrons 3. fluorine-19      _____ protons      _____neutrons  
Determine the element that is represented by the symbol below. (A) iron (B) germanium (C) barium (D) chromium
Which term best characterizes the relationship of hydrogen to deuterium? (A) allotropes (B) isomers (C) isotopes (D) polymers
Lithium has only two naturally occurring isotopes. The mass of lithium-6 is 6.01512 amu and the mass of lithium-7 is 7.01601 amu. Calculate the relative abundances of the two isotopes. 
Gallium consists of two naturally-occurring isotopes, 69Ga and 71Ga, with masses of 68.926 and 70.926 amu, respectively. Given that 69Ga is 60.3% abundant, what is the average molar mass of Ga?
The element X occurs naturally to the extent of 20.0% 12X and 80.0% 13X. The atomic mass of X is nearest (A) 12.2 (B) 12.5 (C) 12.8 (D) 13.0
There are three isotopes of hydrogen, differing with respect to a. atomic mass. b. atomic number. c. nuclear charge. d. electron configuration. e. number of protons.
Magnesium has three naturally occurring isotopes with the following masses and natural abundances: Calculate the atomic mass of magnesium and sketch its mass spectrum. 
Atoms of the same element with different mass numbers are called a. allotropes b. chemical families c. nucleons d. neutrons e. isotopes
An element has four naturally occurring isotopes with the masses and natural abundances given here. Find the atomic mass of the element and identify it. 
Vanadium has two naturally occurring isotopes, 50V with an atomic mass of 49.9472 amu and 51V with an atomic mass of 50.9440. The atomic weight of vanadium is 50.9315. The percent abundances of the vanadium isotopes are _______ % 50V and __________% 51V.  a. 0.25, 99.75 b. 99.75, 0.25 c. 49, 51 d. 1.25, 98.75 e. 99, 1.0
The fictional element kryptonite (lets give it the symbol Kt) associated with Superman's home planet of Krypton could be said to consist of two isotopes with the following abundances. Estimate the approximate atomic mass of kryptonite. Kt  285; 70.0% Kt  289; 30.0% a. 288.2 amu b. 286.2 amu c. 284,6 amu d. 282.6 amu e. 280.3 amu
Silicon has three naturally occurring isotopes (Si-28, Si-29, and Si-30). The mass and natural abundance of Si-28 are 27.9769 amu and 92.2%, respectively. The mass and natural abundance of Si-29 are 28.9765 amu and 4.67%, respectively. Find the mass and natural abundance of Si-30. 
Which box below represent isotopes of each other (each box represents a single atom)? A. I and II B. II and III C. II and IV D. III and IV E. I and III
Naturally occurring cobalt consists of only one isotope,  59Co, whose relative atomic mass is 58.9332. A synthetic radioactive isotope of cobalt, 60Co, relative atomic mass 59.9338, is used in radiation therapy for cancer. A 1.5886-g sample of cobalt has an apparent "atomic mass" of 58.9901. Find the mass of 60Co in this sample. 
Silver has an atomic mass of 107.868 amu and only two naturally-occurring isotopes. The Ag-109 isotope (108.905 amu) has a natural abundance of 48.16%. What is the mass (in amu) of the other isotope? Express your final answer using 6 significant figures. A. 106.911 amu B. 106.908 amu C. 106.903 amu D. 106.905 amu E. 106.899 amu
Boron has two naturally occurring isotopes, 10B has a mass of 10.013 amu and 11B has a mass of 11.009 amu. What is the natural or % abundance of the  10B isotope? 
Fill in the requested information. a) How many protons, electrons and neutrons does tin(IV)-120 have?   b) Write the atomic symbol for the tin isotope in a).   c) What is the mass number of the isotope of rubidium that has 49 neutrons?   d) Which neutral element could have an isotope with 38 neutrons for a mass number of 72?
The number of ____defines the element; and isotopes differ in the number of ______. A. electrons; neutrons B. protons; neutrons C. protons; electrons D. neutrons; protons E. electrons; protons
Determine the number of protons, neutrons and electrons in the following: A) p+= 18 n° = 22 e- = 40 B) p+= 40 n° = 22 e- = 18 C) p+= 18 n° = 22 e- = 18 D) p+= 18 n° = 18 e- = 2 E) p+= 22 n° = 18 e- = 18
Chlorine has 2 naturally occurring isotopes, Cl-35 and Cl-37.  Which is generally true?  a)  Cl-35 has the greater abundance. b)  The relative abundances are the same. c)  The relative abundances are never known. d)  Cl-37 has the greater abundance. e)  There has to be a third naturally occurring isotope. 
Gallium has two naturally occurring isotopes, 69Ga and 71Ga, with masses of 68.9257 amu and 70.9249 amu, respectively.  Calculate the % abundance of the two isotopes of Ga.   Atomic Mass of Ga = 69.723 amu 
In which pair are the two species  both isoelectronic and isotopic? 
Only three isotopes of magnesium exist on earth. 24Mg is the most common form at 78.70% natural abundance with a mass of 23.98504 amu, 25Mg has a 10.13% natural abundance, while 26Mg has a natural abundance of 11.17% and a mass of 25.98259 amu. What is the mass of the 25Mg isotope?
Sulfur has four isotopes: S–32 (31.97 amu), S–33 (32.97 amu), S–34 (33.97 amu), and S–36 (35.97 amu). Which of these isotopes is the most abundant?       1. S–32              2. S–33              3. S–34              4. S–36
The atomic masses in the periodic table are not integral numbers. For example, carbon is listed as 12.01115 instead of 12.00000. What is the reason for this? A. Atoms gain and lose electrons easily, significantly changing their masses. B. Measurements taken of atomic samples are contaminated with other elements. C. Technology does not allow for exact measurements of such small quantities. D. The listed values are weighted averages of naturally occurring isotopes. E. There is a theoretical uncertainty in the masses of atoms.
Which of the following statements about isotopes is TRUE? A) Isotopes of the same element don't usually have the same properties. 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 differ only in the number of electrons they contain. D) Isotopes of the same element have the same mass. E) Some elements have 3 or more naturally occurring isotopes.
Suppose the element Z contains only two isotopes, 29Z (atomic mass 28.933 amu, abundance 43.03%) and 31Z (atomic mass 30.916 amu). What would be the atomic mass of Z that would appear in the periodic table?
A naturally occurring sample of an element contains only two isotopes. The first isotope has a mass of 68.9255 amu and a natural abundance of 60.11%. The second isotope has a mass of 70.9247 amu. Find the atomic mass of the element. a) 70.13 amu b) 69.72 amu c) 84.06 amu d) 69.93 amu
Conventional breeder reactors (oxymoron?) make more nuclear fuel from the isotopes they consume. For example, plutonium-239 converts thorium-232 to plutonium-239, which can be used to power another breeder reactor.  Give the number of protons and neutrons in the following isotopes:  thorium-232 ____ protons     _____ neutrons 
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) 108.19 amu B) 107.90 amu C) 108.32 amu D) 108.00 amu E) 107.79 amu
Conventional breeder reactors (oxymoron?) make more nuclear fuel from the isotopes they consume. For example, plutonium-239 converts thorium-232 to plutonium-239, which can be used to power another breeder reactor.  Give the number of protons and neutrons in the following isotopes:  thorium-239 ____ protons     _____ neutrons 
The element X has three naturally occuring isotopes;  aX, bX, and cX, where a, b, and c represent the mass number. The masses (amu),except aX, and the percent abundances of the isotopes are given in the table below. The average atomic mass of X is 17.20 amu. What is the mass of aX in amu? a. 16.60 b. 16.67 c. 19.01 d. 18.11 e. 9.99
The atomic masses of 6Li and 7Li are 6.0151 amu and 7.0160 amu, respectively. Calculate the natural abundances of these two isotopes. The average atomic mass of Li is 6.941 amu.
The nucleus of 6Li is a powerful absorber of neutrons. It exists in the naturally occurring metal to the extent of 7.5%. In the era of nuclear deterrence, large quantities of lithium were processed to remove 6Li for use in hydrogen bomb production. The lithium metal remaining after removal of 6Li was sold on the market.What are the compositions of the nuclei of 6Li? How many protons does 6Li have?
The nucleus of 6Li is a powerful absorber of neutrons. It exists in the naturally occurring metal to the extent of 7.5%. In the era of nuclear deterrence, large quantities of lithium were processed to remove 6Li for use in hydrogen bomb production. The lithium metal remaining after removal of 6Li was sold on the market.What are the compositions of the nuclei of 7Li? How many neutrons does 7Li have?
The nucleus of 6Li is a powerful absorber of neutrons. It exists in the naturally occurring metal to the extent of 7.5%. In the era of nuclear deterrence, large quantities of lithium were processed to remove 6Li for use in hydrogen bomb production. The lithium metal remaining after removal of 6Li was sold on the market.What are the compositions of the nuclei of 7Li? How many protons does 7Li have?
The natural abundance of 3 He is 0.000137 %.How many protons, neutrons, and electrons are in an atom of 3 He?
Determine the number of protons and neutrons in each of the following isotopes.714 N
Determine the number of protons and neutrons in each of the following isotopes.1123 Na
Determine the number of protons and neutrons in each of the following isotopes.82208 Pb
Determine the number of protons and neutrons in each of the following isotopes.86222 Rn
The amount of carbon-14 in artifacts and fossils is often used to establish their age.Determine the number of protons and neutrons in a carbon-14 isotope.
Hydrogen has three isotopes (1H, 2H, and 3H), and chlorine has two isotopes (35Cl and 37Cl).Tell how many protons, neutrons, and electrons 1H35Cl contains.
Hydrogen has three isotopes (1H, 2H, and 3H), and chlorine has two isotopes (35Cl and 37Cl).Tell how many protons, neutrons, and electrons 1H37Cl contains.
Hydrogen has three isotopes (1H, 2H, and 3H), and chlorine has two isotopes (35Cl and 37Cl).Tell how many protons, neutrons, and electrons 2H37Cl contains.
Hydrogen has three isotopes (1H, 2H, and 3H), and chlorine has two isotopes (35Cl and 37Cl).Tell how many protons, neutrons, and electrons 3H35Cl contains.
Hydrogen has three isotopes (1H, 2H, and 3H), and chlorine has two isotopes (35Cl and 37Cl).Tell how many protons, neutrons, and electrons 3H37Cl contains.
The first atoms of seaborgium (Sg) were identified in 1974. The longest-lived isotope of Sg has a mass number of 266.How many protons, electrons, and neutrons are in an 266Sg atom?
The two most common isotopes of uranium are 235U and 238U.Compare the number of protons, the number of electrons, and the number of neutrons in atoms of these two isotopes.
The radioactive isotope cesium-137 was produced in large amounts in fallout from the 1986 nuclear power-plant disaster at Chernobyl, Ukraine.Write the symbol for this isotope in standard format.
Write symbols for the following isotopes.Radon-220
Write symbols for the following isotopes.Polonium-210
Write symbols for the following isotopes.Gold-197
Write symbols for the following isotopes.Z = 27 and A = 60
Write the correct symbol, with both superscript and subscript, for each of the following. Use the list of elements inside the front cover as needed:the isotope of platinum that contains 118 neutrons
The table below gives the number of protons (p) and neutrons (n) for four isotopes. (i) (ii) (iii) (iv) p 19 19 20 20 n 19 21 19 20 Write the symbol for the isotope (i).
Write the correct symbol, with both superscript and subscript, for each of the following. Use the list of elements inside the front cover as needed:the isotope of krypton with mass number 84
Write the correct symbol, with both superscript and subscript, for each of the following. Use the list of elements inside the front cover as needed:the isotope of arsenic with mass number 75
Write the correct symbol, with both superscript and subscript, for each of the following. Use the list of elements inside the front cover as needed:the isotope of magnesium that has an equal number of protons and neutrons
The table below gives the number of protons (p) and neutrons (n) for four isotopes. (i) (ii) (iii) (iv) p 19 19 20 20 n 19 21 19 20 Write the symbol for the isotope (ii).
The table below gives the number of protons (p) and neutrons (n) for four isotopes. (i) (ii) (iii) (iv) p 19 19 20 20 n 19 21 19 20 Write the symbol for the isotope (iii).
The table below gives the number of protons (p) and neutrons (n) for four isotopes. (i) (ii) (iii) (iv) p 19 19 20 20 n 19 21 19 20 Write the symbol for the isotope (iv).
Write isotopic symbols of the form ZA X for each isotope.the sodium isotope with 12 neutrons
Write isotopic symbols of the form ZA X for each isotope.the oxygen isotope with 8 neutrons
Write isotopic symbols of the form ZA X for each isotope.the aluminum isotope with 14 neutrons
Write isotopic symbols of the form ZA X for each isotope.the iodine isotope with 74 neutrons
The amount of carbon-14 in artifacts and fossils is often used to establish their age.Write its symbol in the form ZA X.
The element oxygen has three naturally occurring isotopes, with 8, 9, and 10 neutrons in the nucleus, respectively.Write the full chemical symbols for these three isotopes.
Element X is toxic to humans in high concentration but is essential to life in low concentrations. Write the symbol for the isotope of X that has 28 neutrons.
Silver is composed of two naturally occurring isotopes: Ag-107 (51.839%) and Ag-109. The ratio of the masses of the two isotopes is 1.0187.What is the mass of Ag-107?
Magnesium has three naturally occurring isotopes: 24 Mg (23.985 amu) with 78.99% abundance, 25 Mg (24.986 amu) with 10.00% abundance, and a third with 11.01% abundance.Look up the atomic weight of magnesium, and then calculate the mass of the third isotope.
Carbon has two naturally occurring isotopes: C-12 (natural abundance is 98.93%; mass is 12.0000 amu) and C-13 (natural abundance is 1.07%; mass is 13.0034 amu).Without doing any calculations, determine which mass is closest to the atomic mass of carbon.
In a naturally occurring sample, 19.8% of boron atoms have five neutrons and 80.2% have six neutrons. What is the mass of a boron atom containing 5 neutrons?
In a naturally occurring sample, 19.8% of boron atoms have five neutrons and 80.2% have six neutrons. What is the mass of a boron atom containing 6 neutrons?
Magnesium has three naturally occurring isotopes with the following masses and natural abundances: Isotope Mass (amu) Abundance (%) Mg-24 23.9850 78.99 Mg-25 24.9858 10.00 Mg-26 25.9826 11.01 Calculate the atomic mass of magnesium.
An element has two naturally occurring isotopes. Isotope 1 has a mass of 120.9038 amu and a relative abundance of 57.4%, and isotope 2 has a mass of 122.9042 amu.By comparison to the periodic table, identify this element.
Copper has two naturally occurring isotopes, including 65Cu.Look at the periodic table and tell what is the second isotope?
What isotope is used as the standard in establishing the atomic mass scale?
The atomic weight of boron is reported as 10.81, yet no atom of boron has the mass of 10.81 amu. Explain.
The explosion of an atomic bomb releases many radioactive isotopes, including strontium-90. Considering the location of strontium in the periodic table, suggest a reason for the fact that this isotope is particularly dangerous for human health.
What are isotopes?
What is percent natural abundance?
Describe the two different notations used to specify isotopes and give an example of each.
The atomic mass of copper is 63.546 amu.Do any copper isotopes have a mass of 63.546 amu?
Boron has only two naturally occurring isotopes. The mass of boron-10 is 10.01294 amu and the mass of boron-11 is 11.00931 amu .Use the atomic mass of boron to calculate the relative abundance of boron-10.
A sample of naturally occurring silicon consists of 28Si (27.9769 amu), 29Si (28.9765 amu), and 30Si (29.9738 amu). The atomic weight of silicon is 28.0855 amu and the natural abundance of 29Si is 4.68 %.What is the natural abundances of 28Si?
A sample of naturally occurring silicon consists of 28Si (27.9769 amu), 29Si (28.9765 amu), and 30Si (29.9738 amu). The atomic weight of silicon is 28.0855 amu and the natural abundance of 29Si is 4.68 %.What is the natural abundances of 30Si?
Gallium has two naturally occurring isotopes: gallium-69 (isotopic mass = 68.926) and gallium-71 (isotopic mass = 70.925). The atomic weight of gallium is 69.723.Calculate the percent abundance of gallium-69.
Copper metal has two naturally occurring isotopes: copper-63 (69.15%; isotopic mass = 62.93) and copper-65 (30.85%; isotopic mass = 64.93). Calculate the atomic weight of copper.
An unknown element, X, has three naturally occurring isotopes. The masses of the threee isotropes are 22.356, 23.492, and 26.106. The first two have a percent abundance of 55.230% and 28.015%, respectively. What is the average mass of the element? A) 23.303 B) 26.242 C) 23.986 D) 18.929 E) 24.934
The mass number of an isotope is A. The number of protons in the nucleus B. The number of neutrons in the nucleus C. The number of electrons in the nucleus D. The sum of the number of protons and neutrons in the nucleus E. The sum of the number of protons and electrons in the nucleus
Natural rubidium has the average mass of 85.4678 and is composed of isotopes 85Rb (mass = 84.9117) and 87Rb. The ratio of atoms 85Rb/87Rb in natural rubidium is 2.591. Calculate the mass of 87Rb.
An element consists of 1.40% of an isotope with mass 203.973 amu, 24.10% of an isotope with mass 205.9745 amu, 22.10% of an isotope with mass 206.9759 amu, and 52.40% of an isotope with mass 207.9766 amu. Calculate the average atomic mass and identify the element.
Write isotopic symbols of the form X-A (for example, C-13) for each isotopes.a.. the iodine isotope with 74 neutronsb. the phosphorus isotope with 16 neutronsc. the uranium isotope with 234 neutronsd. the argon isotope with 22 neutrons
The element rhenium (Re) has two naturally occurring isotopes, 185Re and 187Re, with an average atomic mass of 186.207 amu. Rhenium is 62.60% 187Re, and the atomic mass of 187Re is 186.956 amu. Calculate the mass of 185Re.
Assume silicon has three major isotopes in nature as shown in the table below. Fill in the missing information.Isotope                            Mass (amu)                   Abundance28Si                                     27.98                           ——––—29Si                                   ——––—                          4.70%32Si                                     29.97                              3.09%
The element europium exists in nature as two isotopes:  151Eu has a mass of 150.9196 amu, and 153Eu has a mass of 152.9209 amu. The average atomic mass of europium is 151.96 amu. Calculate the relative abundance of the two europium isotopes.
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 amub. 46.84 amuc. 45.91 amud. 44.99 amue. 46.34 amu
The table below describes four atoms. Which atoms represent the same element?A) A and B represent the same elementB) A and C represent the same elementC) A and D represent the same elementD) B and C represent the same elementE) C and D represent the same element
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 amuB) 69.93 amuC) 70.00 amuD) 69.80 amuE) 70.68 amu
Determine the number of protons and neutrons in each  isotope.
Give the nuclear symbol for the isotope of beryllium for which A = 10?
Which of the following atoms contains the fewest protons?a. 46Tib. 47Tic. 49Tid. 50Tie. all contain the same number of protons. 
Which of the following statements is FALSE?(A) an atom consists of a positively charged, massive nucleus that occupies very little volume and electrons that go round the nucleus(B) the number of electrons in an atom is equal to the number of protons(C) the mass of an atom is equal to the number of protons + the number of neutrons(D) isotopes of an atom contain different numbers of electrons(E) the mass of a proton is approximately the same as the mass of a neutron
Which two of the atoms below have the same number of neutrons?
I think I discovered element 120, which would be the last element in the 2A column. It consists of two isotopes. The abundance of the first isotope is 68.00% and its atomic mass is 294.6 u. The abundance of the second isotope is _________ (you can figure this out since there are only two isotopes) and its atomic mass is 297.8 u. What is the average atomic mass of the element? a. 296.2 u b. 295.0 u c. 296.8 u d. 295.6 u e. 297.4 u  
There are two isotopes of the element gallium that appear in nature, 69Ga (M = 68.926 amu) and 71Ga (M = 70.924 amu). Given that the average atomic mass for gallium is M = 69.72 amu, what is the percent by number of the 69Ga isotope in naturally occurring gallium?A. 39.7%B. 97.0%C. 50.0%D. 60.3%E. 98.9%
Rank from highest to lowest molecular mass:D216O17O                 T 218O2                               D216O2  D218O2                         T216O2                                  H217O2T217O2                          H216O17O                     H  218O2
Which of the following represent isotopes? I: 3215X     II: 3216X     III: 3115X     IV: 3417X a. I and II b. I and IV c. I and III d. III and IV
Assume that a new element has only two isotopes E-182 and E-186 and its atomic mass is 184.3 amu. Which isotope is more abundant? a. E-182 b. E-186 c. I need more information to decide. 
Bromine has two naturally occurring isotopes. One of them, bromine-79, has a mass of 78.9183 amu and a natural isotopic abundance of 50.69%. Calculate the m/m % of the other isotope, bromine-81. Note: m/m % stands for the mass of Br-81 in grams contained in 100 grams of bromine element. 
What isotope has 18 protons and 22 neutrons?
The atomic mass of copper is 63.546 amu. Do any copper isotopes have a mass of 63.546 amu? Explain.
Give the nuclear symbol for the isotope of potassium for which  A=40
What isotope has 14 protons and 14 neutrons? Enter the name of the element followed by a hyphen and the mass number (e.g., uranium-234).
Which of the following answers give the correct number of subatomic particles for the isotope given below?a. 13 protons, 27 neutrons and 13 electronsb. 13 protons, 14 neutrons and 16 electronsc. 13 protons, 14 neutrons and 10 electronsd. 27 protons, 13 neutrons and 13 electrons
Give the nuclear symbol (isotope symbol) for the isotope of bromine, Br, that contains 46 neutrons per atom. 
The element antimony has an atomic weight of 121.757 amu and only two naturally occurring isotopes. One isotope has an abundance of 57.3% and an isotopic mass of 120.904 amu. What is the mass of the other isotope? A) 52.479 amu B) 121.757 amu C) 122.393 amu D) 122.610 amu E) 122.902 amu
Which of the following  contains a pair of isotopes?
Osmium has six naturally occurring isotopes. When the most abundant isotope has this symbol:190Os6+The atomic number (Z), mass number (A), number of neutron (n) and number of electrons are:A) Z=76, A=114, n=190, e=76B) Z=190, A=76, n=114, e=76C) Z=76, A=76, n=114, e=82D) Z=76, A=190, n=114, e=70
On another planet, the isotopes of titanium have the following natural abundances. What is the average atomic mass of titanium on that planet?Isotope: 46Ti Abundance: 75.200% Mass: 45.95263 amuIsotope: 48Ti Abundance: 12.300% Mass: 47.94795 amuIsotope: 50Ti Abundance: 12.500% Mass: 49.94479 amu
An isotope of an element contains 82 protons and 122 neutrons. What is the symbol for the isotope? 
The atomic masses of Boron-10 and Boron-11 are 10.012938 and 11.009305 amu, respectively. The average atomic mass of boron is 10.811 amu. Calculate the natural abundances of these two isotopes.
Which of the following represent isotopes? A) A and D      B) A and B      C) C and D      D) A and C
Which of the following pairs of atoms represent isotopes?      A) H-1, O-18      B) N-14, C-14      C) Br-79, Cl-35      D) C-12, C-14      E) Se-77, F-19
Indicate the number of protons and neutrons in the following nuclei.2456 Mn
Indicate the number of protons and neutrons in the following nuclei.193 Tl
Indicate the number of protons and neutrons in the following nuclei.argon-38
Indicate the number of protons and neutrons in the following nuclei.The number of protons in the nuclide 12953I
Indicate the number of protons and neutrons in the following nuclei.The number of protons in the nuclide 138Ba
Indicate the number of protons and neutrons in the following nuclei.The number of protons in the nuclide neptunium-237
Indicate the number of protons and neutrons in the following nuclei.The number of neutrons in the nuclide 12953I
Indicate the number of protons and neutrons in the following nuclei.The number of neutrons in the nuclide 138Ba
The isotope of an unknown element, X, has a mass number of 79. The most stable ion of this isotope has 36 electrons and has a 2- charge. Which of the following statements is(are) true? For the false statements, correct them.a. This ion has more electrons than protons in the nucleus.b. The isotope of X contains 38 protons.c. The isotope of X contains 41 neutrons.d. The identity of X is strontium, Sr.
Indicate the number of protons and neutrons in the following nuclei.The number of neutrons in the nuclide neptunium-237
Each of the following isotopes is used in medicine. Indicate the number of protons and neutrons in each isotope.phosphorus-32
Each of the following isotopes is used in medicine. Indicate the number of protons and neutrons in each isotope.chromium-51
Each of the following isotopes is used in medicine. Indicate the number of protons and neutrons in each isotope.cobalt-60
Each of the following isotopes is used in medicine. Indicate the number of protons and neutrons in each isotope.technetium-99
Each of the following isotopes is used in medicine. Indicate the number of protons and neutrons in each isotope.iodine-131
Each of the following isotopes is used in medicine. Indicate the number of protons and neutrons in each isotope.thallium-201
For carbon-14 and carbon-12, how many protons and neutrons are in each nucleus? Assuming neutral atoms, how many electrons are present in an atom of carbon-14 and in an atom of carbon-12?
Name the element and determine the number of protons, neutrons, and electrons in the following isotopes that are used in medical diagnoses: (a) atomic number 9, mass number 18, charge of 1−
Name the element and determine the number of protons, neutrons, and electrons in the following isotopes that are used in medical diagnoses: (b) atomic number 43, mass number 99, charge of 7+
Name the element and determine the number of protons, neutrons, and electrons in the following isotopes that are used in medical diagnoses: (c) atomic number 53, atomic mass number 131, charge of 1−
Name the element and determine the number of protons, neutrons, and electrons in the following isotopes that are used in medical diagnoses: (d) atomic number 81, atomic mass number 201, charge of 1+
Chlorine has two naturally occurring isotopes, 35Cl and 37Cl. What is the mass number of each isotope? How many protons, neutrons, and electrons are present in each?
The following are properties of isotopes of two elements that are essential in our diet. Determine the number of protons, neutrons and electrons in each and name them.(b) atomic number 53, mass number 127, charge of 1−
Determine the number of protons and neutrons in the isotope Fe-58.
Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:
Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:
Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:
Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:
Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:
Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:
Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:
Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:
Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:
Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:
Nuclei differ in their stability, and some are so unstable that they undergo radioactive decay. The ratio of the number of neutrons to number of protons (N/Z) in a nucleus correlates with its stability. (e) The radioactive isotope 238U decays in a series of nuclear reactions that includes another uranium isotope, 234U, and three lead isotopes, 214Pb, 210Pb, and 206Pb. How many neutrons, protons, and electrons are in each of these five isotopes?
A certain element has only two naturally occurring isotopes: one with 18 neutrons and the other with 20 neutrons. The element forms 12 charged ions when in ionic compounds. Predict the identity of the element. What number of electrons does the 12 charged ion have?
Hydrogen has three isotopes (1H, 2H, and 3H), and chlorine has two isotopes (35Cl and 37Cl).Tell how many protons, neutrons, and electrons 2H35Cl contains.
Gallium (Ga) consists of two naturally occurring isotopes with masses of 68.926 and 70.925 amu.How many protons and neutrons are in the nucleus of an isotope with mass of 68.926 amu?
Gallium (Ga) consists of two naturally occurring isotopes with masses of 68.926 and 70.925 amu.How many protons and neutrons are in the nucleus of an isotope with mass of 70.925 amu?
Consider an atom of 10B.(b) What is the symbol of the atom obtained by adding one proton to 10B?(c) What is the symbol of the atom obtained by adding one neutron to 10B?Are either of the atoms obtained in parts B and C isotopes of 10B? If so, which one?
(a) Which two of the following are isotopes of the same element: 3116X, 3115X, 3216X?What is the identity of the element whose isotopes you have selected?
Representations of three nuclei (with neutrons gray and protons purple) are shown below. Nucleus 1 is stable, but 2 and 3 are not. (a) Write the symbol for each isotope. 
Write the atomic symbol  for each of the following isotopes.a. Z = 8, number of neutrons = 9
Write the atomic symbol  for each of the following isotopes.b. the isotope of chlorine in which A = 37
Write the atomic symbol  for each of the following isotopes.c. Z = 27, A = 60
Write the atomic symbol  for each of the following isotopes.d. number of protons = 26, number of neutrons = 31
Write the atomic symbol  for each of the following isotopes.e. the isotope of I with a mass number of 131
Write the atomic symbol  for each of the following isotopes.f. Z = 3, number of neutrons = 4
Write the atomic symbol  for each of the isotopes described below.b. the isotope of boron with mass number 10
Write the atomic symbol  for each of the isotopes described below.c. Z = 12, A = 23
Write the atomic symbol  for each of the isotopes described below.d. atomic number 53, number of neutrons = 79
Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each.(a) the alkali metal with 11 protons and a mass number of 23
Write the atomic symbol  for each of the isotopes described below.e. Z = 20, number of neutrons = 27
Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each.(b) the noble gas element with 75 neutrons in its nucleus and 54 electrons in the neutral atom
Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each.(c) the isotope with 33 protons and 40 neutrons in its nucleus
Write the atomic symbol  for each of the isotopes described below.f. number of protons = 29, mass number 65
Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each.(d) the alkaline earth metal with 88 electrons and 138 neutrons
An isotope of an element contains 82 protons and 122 neutrons.What is the symbol for the isotope?
Uranium-235 is used in nuclear fission.Enter its symbol in the form ZAX.
Antimony has many uses, for example, in infrared devices and as part of an alloy in lead storage batteries. The element has two naturally occurring isotopes, one with mass 120.904 amu and the other with mass 122.904 amu. (a) Write the AZX notation for each isotope. 
Enter isotopic symbols of the form X-A (e.g., C-13) for each isotope.The silver isotope with 60 neutrons
Enter isotopic symbols of the form X-A (e.g., C-13) for each isotope.The silver isotope with 62 neutrons
Enter isotopic symbols of the form X-A (e.g., C-13) for each isotope.The uranium isotope with 146 neutrons
Enter isotopic symbols of the form X-A (e.g., C-13) for each isotope.  The hydrogen isotope with 1 neutron
What is the symbol (including the atomic number, mass number, and element symbol) for the carbon isotope with 7 neutrons?
Gallium (Ga) consists of two naturally occurring isotopes with masses of 68.926 and 70.925 amu.Write the complete atomic symbol for each, showing the atomic number and mass number.
Which element does X represent in the following expression? Enter the chemical symbol of the element.
What is the mass in amu of a carbon-12 atom?
Rubidium has two naturally occurring isotopes, rubidium-85 (atomic mass = 84.9118 amu; abundance = 72.15%) and rubidium-87 (atomic mass = 86.9092 amu; abundance = 27.85%).Calculate the atomic weight of rubidium.
Naturally occurring magnesium has the following isotopic abundances:IsotopeAbundance Atomic mass (amu) 24 Mg78.99%23.9850425 Mg10.00%24.9858426 Mg11.01%25.98259What is the average atomic mass of Mg?
Naturally occurring chlorine is composed of two isotopes: 75.76 % Cl-35 (mass of 34.9688 amu) and 24.24 % Cl-37(mass of 36.9659 amu). Naturally occurring oxygen is composed of three isotopes: 99.757% O-16 (mass of 15.9949 amu), 0.038% O-17 (mass of 16.9991 amu), and 0.205% O-18 (mass of 17.9991 amu). The compound dichloromonoxide is composed of two chlorine atoms and one oxygen atom bonded together to form the Cl2O molecule.Give the masses of the three most abundant Cl2O molecules.
The nucleus of 6Li is a powerful absorber of neutrons. It exists in the naturally occurring metal to the extent of 7.5%. In the era of nuclear deterrence, large quantities of lithium were processed to remove 6Li for use in hydrogen bomb production. The lithium metal remaining after removal of 6Li was sold on the market.The atomic masses of 6Li and 7Li are 6.015122 and 7.016004 amu, respectively. A sample of lithium depleted in the lighter isotope was found on analysis to contain 1.442% 6Li. What is the average atomic weight of this sample of the metal?
An element “X” has five major isotopes, which are listed below along with their abundances. What is the element?
Assume silicon has three major isotopes in nature as shown in the table below. Fill in the missing information.
Gallium has two naturally occurring isotopes, 69Ga (isotopic mass = 68.9256 amu, abundance = 60.11%) and 71Ga (isotopic mass = 70.9247 amu, abundance = 39.89%). Calculate the atomic mass of gallium.
Magnesium has three naturally occurring isotopes, 24Mg (isotopic mass = 23.9850 amu, abundance = 78.99%), 25Mg (isotopic mass = 24.9858 amu, abundance = 10.00%), and 26Mg (isotopic mass = 25.9826 amu, abundance = 11.01%). Calculate the atomic mass of magnesium.
The element silver (Ag) has two naturally occurring isotopes: 109Ag and 107Ag with a mass of 106.905 u. Silver consists of 51.82% 107Ag and has an average atomic mass of 107.868 u. Calculate the mass of 109Ag.
Naturally occurring silver consists of two isotopes: 107Ag (51.84%) with an isotopic mass of 106.9051 amu and 109Ag (48.16%) with an isotopic mass of 108.9048 amu.What is the atomic weight of silver?
An element has the following natural abundances and isotopic masses: 90.92% abundance with 19.99 amu, 0.26% abundance with 20.99 amu, and 8.82% abundance with 21.99 amu. Calculate the average atomic mass of this element.
Variations in average atomic mass may be observed for elements obtained from different sources. Lithium provides an example of this. The isotopic composition of lithium from naturally occurring minerals is 7.5% 6Li and 92.5% 7Li, which have masses of 6.01512 amu and 7.01600 amu, respectively. A commercial source of lithium, recycled from a military source, was 3.75% 6Li (and the rest 7Li). Calculate the average atomic mass values for each of these two sources.
Bromine has two naturally occurring isotopes (Br-79 and Br-81) and has an atomic mass of 79.904 amu. The mass of Br-81 is 80.9163 amu, and its natural abundance is 49.31%. Calculate the mass of Br-79ext{Br-79}.
Naturally occurring iodine has an atomic mass of 126.9045 amu. A 12.3849-g sample of iodine is accidentally contaminated with 1.00070 g of 129I, a synthetic radioisotope of iodine used in the treatment of certain diseases of the thyroid gland. The mass of 129I is 128.9050 amu.Find the apparent "atomic mass" of the contaminated iodine.
Magnesium has three naturally occurring isotopes with masses of 23.99 amu, 24.99 amu, and 25.98 amu and natural abundances of 78.99 %, 10.00 %, and 11.01 %, respectively. Calculate the atomic mass of magnesium.
Gallium has two naturally occurring isotopes: Ga-69 with a mass of 68.9256 amu and a natural abundance of 60.11 %, and Ga-71. Use the atomic mass of gallium listed in the periodic table to determi