2. Atoms & Elements

Atomic Mass

2. Atoms & Elements

Atomic Mass

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Atomic Mass Example 1

Atomic Mass Example 2

Atomic Mass Example 3

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Multiple Choice

Which of the following choices has the greatest atomic mass?

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Multiple Choice

Neon possesses three naturally occurring isotopes. ²⁰Ne has a percent abundance of 90.48% and an isotopic mass of 19.99244 amu, ²¹Ne has a percent abundance of 0.27% and an isotopic mass of 20.99384 amu, and ²²Ne has a percent abundance of 9.25%. What is the isotopic mass of the ²²Ne isotope?

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Multiple Choice

Three isotopic forms of potassium exist: ³⁹K, ⁴⁰K and ⁴¹K. Potassium has an atomic mass of 39.0983 amu. Potassium-40 has an isotopic mass of 39.9640 amu and natural abundance of 0.0117%. Potassium-41 has an isotopic mass of 40.9618 amu and natural abundance of 6.7302%. What is the isotopic mass of Potassium-39?

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Textbook Question

The following diagram is a representation of 20 atoms of a fictitious element, which we will call nevadium (Nv). The red spheres are 293Nv, and the blue spheres are 295Nv. (b) If the mass of 293Nv is 293.15 u and that of 295Nv is 295.15 u, what is the atomic weight of Nv?

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Textbook Question

The following diagram is a representation of 20 atoms of a fictitious element, which we will call nevadium (Nv). The red spheres are 293Nv, and the blue spheres are 295Nv. (a) Assuming that this sample is a statistically representative sample of the element, calculate the percent abundance of each element.

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Textbook Question

What is the atomic weight of an element that consists of two naturally occurring isotopes? The first isotope has a mass of 84.911 and an abundance of 72.17% and the second isotope has a mass of 86.909 and an abundance of 27.83%. (LO 2.15) (a) 85.47 (b) 86.35 (c) 85.91 (d) 85.17

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Textbook Question

(a) What isotope is used as the standard in establishing the atomic mass scale?

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Textbook Question

(b) Why is the atomic weight of carbon reported as 12.011 in the table of elements and the periodic table in the front inside cover of this text?

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Textbook Question

Iron has three major isotopes: 54Fe (atomic mass = 53.9396 u; abundance 5.85%), 56Fe (atomic mass = 55.9349 u; abundance 91.75%), and 57Fe (atomic mass = 56.9354 u; abundance 2.12 %). Calculate the atomic weight (average atomic mass) of iron.

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Textbook Question

Bromine has two naturally occurring isotopes, bromine-79 1atomic mass = 78.9183 u; abundance = 50.69%2 a n d bromine-81 1atomic mass = 80.9163 u; abundance = 49.31%2. Calculate the atomic weight of bromine.

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Textbook Question

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. Find the atomic mass of this element and identify it.

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Textbook Question

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. Isotope Mass (amu) Abundance (%) 1 135.90714 0.19 2 137.90599 0.25 3 139.90543 88.43 4 141.90924 11.13

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Textbook Question

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 and natural abundance of Br-79.

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Textbook Question

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Textbook Question

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.

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Textbook Question

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. (b) The atomic masses of 6Li and 7Li are 6.015122 and 7.016004 u, 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?

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Textbook Question

The element chromium (Cr) consists of four naturally occurring isotopes with atomic masses 49.9460, 51.9405, 52.9407, and 53.9389 u. The relative abundances of these four isotopes are 4.3, 83.8, 9.5, and 2.4%, respectively. From these data, calculate the atomic weight of chromium.

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Textbook Question

Copper (Cu) consists of two naturally occurring isotopes with masses of 62.9296 and 64.9278 u. (a) How many protons and neutrons are in the nucleus of each isotope? Write the complete atomic symbol for each, showing the atomic number and mass number. (b) The average atomic mass of Cu is 63.55 u. Calculate the abundance of each isotope.

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Textbook Question

What is the difference between an element's atomic number and its atomic weight?

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Textbook Question

There are two different isotopes of bromine atoms. Under normal conditions, elemental bromine consists of Br2 molecules, and the mass of a Br2 molecule is the sum of the masses of the two atoms in the molecule. The mass spectrum of Br2 consists of three peaks: Mass (u) Relative Size 157.836 0.2569 159.834 0.4999 161.832 0.2431 (b) What is the mass of each isotope?

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Textbook Question

Iodine has a lower atomic mass than tellurium (126.90 for iodine, 127.60 for tellurium) even though it has a higher atomic number (53 for iodine, 52 for tellurium). Explain.

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Textbook Question

Naturally occurring iodine has an atomic mass of 126.9045 amu. A 12.3849 g sample of iodine is accidentally contaminated with an additional 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.

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Textbook Question

The unified atomic mass unit (u) 1/12 the mass of a neutral atom of: (a) 1^H (b) 12^C (c) 14^C (d) 16^O

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Textbook Question

(a) The unified atomic mass unit (u) is used to represent the extremely small mass of atoms. How many grams are equivalent to 1 u?

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Textbook Question

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. Calculate the relative abundances of the two isotopes.

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Textbook Question

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.

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Textbook Question

Naturally occurring boron consists of two isotopes: 10^B (19.9%) with an isotopic mass of 10.0129 and 11^B (80.1%) with an isotopic mass of 11.009 31. What is the atomic weight of boron? Check your answer by looking at a periodic table.

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Textbook Question

Naturally occurring silver consists of two isotopes: 107^Ag (51.84%) with an isotopic mass of 106.9051 and 109^Ag (48.16%) with an isotopic mass of 108.9048. What is the atomic weight of silver? Check your answer in a periodic table.

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Textbook Question

Magnesium has three naturally occurring isotopes: ²⁴Mg (23.985) with 78.99% abundance, ²⁵Mg (24.986) 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.

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Textbook Question

Naturally occurring chlorine is composed of two isotopes: 75.76% Cl-35 (mass 34.9688 amu) and 24.24% Cl-37 (mass 36.9659 amu). Naturally occurring oxygen is composed of three isotopes: 99.757% O-16 (mass 15.9949 amu), 0.038% O-17 (mass 16.9991 amu), and 0.205% O-18 (mass 17.9991 amu). The compound dichlorine monoxide is composed of two chlorine atoms and one oxygen atom bonded together to form the Cl2O molecule. How many Cl2O molecules of different masses naturally exist? Give the masses of the three most abundant Cl2O molecules.

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Textbook Question

A sample of naturally occurring silicon consists of 28^Si (27.9769), 29^Si (28.9765), and 30^Si (29.9738). If the atomic weight of silicon is 28.0855 and the natural abundance of 29^Si is 4.68%, what are the natural abundances of 28^Si and 30^Si?

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Textbook Question

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?

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Textbook Question

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, and check your answer in the periodic table.

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Textbook Question

Germanium has five naturally occurring isotopes: 70^Ge, 20.5%, 69.924; 72^Ge, 27.4%, 71.922; 73^Ge, 7.8%, 72.923; 74^Ge, 36.5%, 73.921; and 76^Ge, 7.8%, 75.921. What is the atomic weight of germanium?

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Textbook Question

Prior to 1961, the atomic mass unit (amu) was defined as 1/16 the mass of the atomic weight of oxygen; that is, the atomic weight of oxygen was defined as exactly 16. What was the mass of a 12C atom prior to 1961 if the atomic weight of oxygen on today's scale is 15.9994?

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Open Question

Boron has two isotopes, boron-10 and boron-11, whose percentage abundances are 19.8% and 80.2% respectively. the atomic masses of boron-10 and boron-11 are 10.0129 amu and 11.0093 amu respectively. write the symbols for the two isotopes of boron and determine the relative atomic mass.

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Open Question

Boron obtained from borax deposits in death valley consists of two isotopes. They are boron-10 and boron-11 with atomic masses of 10.013 amu and 11.009 amu, respectively. The atomic mass of boron is 10.81 amu (see periodic table). Which isotope of boron is more abundant, boron-10 or boron-11?

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Open Question

Lithium has an elemental atomic mass of 6.941 u and has two naturally occurring isotopes, ⁶Li and ⁷Li. Their masses are 6.0151 u and 7.0160 u respectively. What are the natural abundances (to 2 decimal places in percentage) of the isotopes of lithium?

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Open Question

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%.

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Open Question

Boron has two naturally occurring isotopes