Atomic Mass

The atomic mass of an element is the weighted average of the atomic masses of

• the least abundant isotopes of the element

• the naturally occurring isotopes of the element

• the artificially produced isotopes of the element

• the natural and artificial isotopes of the element

The table below gives the atomic mass and the abundance of the two naturally occurring isotopes of bromine.

Which numerical setup can be used to calculate the atomic mass of the element bromine?

• (78.92 u)(50.69) + (80.92 u)(49.31)

• (78.92 u)(49.31) + (80.92 u)(50.69)

• (78.92 u)(0.5069) + (80.92 u)(0.4931)

• (78.92 u)(0.4931) + (80.92 u)(0.5069)

Tags

NGSS.MS-PS1-1

What information is necessary to determine the atomic mass of the element chlorine?

• the atomic mass of each artificially produced isotope of chlorine, only

• the relative abundance of each naturally occurring isotope of chlorine, only

• the atomic mass and the relative abundance of each naturally occurring and artificially produced isotope of chlorine

• the atomic mass and the relative abundance of each naturally occurring isotope of chlorine

Which value of an element is calculated using both the mass and the relative abundance of each of the naturally occurring isotopes of this element?

• Atomic Number

• Atomic Mass

• Half-life

• Molar Volume

The atomic mass of element A is 63.6 atomic mass units. The only naturally occurring isotopes of element A are A-63 and A-65. The percent abundances in a naturally occurring sample of elementA are closest to

• 31% A-63 and 69% A-65

• 50% A-63 and 50% A-65

• 69% A-63 and 31% A-65

• 100% A-63 and 0% A-65

Hydrogen has three isotopes with mass numbers of 1, 2, and 3 and has an average atomic mass of 1.00794 amu. This information indicates that

• equal numbers of each isotope are present

• more isotopes have an atomic mass of 2 or 3 than of 1

• more isotopes have an atomic mass of 1 than of 2 or 3

• isotopes have only an atomic mass of 1

The average isotopic mass of chlorine is 35.5. Which mixture of isotopes (shown as percents) produces this average mass?

• 50% ¹²C and 50% ¹³C

• 50% ³⁵Cl and 50% ³⁷Cl

• 75% ¹²C and 25% ¹³C

• 75% ³⁵Cl and 25% ³⁷Cl

If 75.0% of the isotopes of an element have a mass of 35.0 amu and 25.0% of the isotopes have a mass of 37.0 amu, what is the atomic mass of the element?

• 35.0 amu

• 36.0 amu

• 35.5 amu

• 37.0 amu

Tags

NGSS.MS-PS1-2

Some information about the two naturally occurring isotopes of gallium is given in the table below. Which numerical setup can be used to calculate the atomic mass of gallium?

• (0.6011)(68.926 u) + (0.3989)(70.925 u)

• (60.11)(68.926 u) + (39.89)(70.925 u)

• (0.6011)(70.925 u) + (0.3989)(68.926 u)

• (60.11)(70.925 u) + (39.89)(68.926 u)