Calculating Atomic Mass Using Table 4.7, calculate the atomic mass for magnesium using the weighted average mass method. Table 4.7 Isotopes of Magnesium Atomic Symbol [latex]{}^{24}_{12}Mg[/latex] [latex]{}^{25}_{12}Mg[/latex] [latex]{}^{26}_{12}Mg[/latex] Name Mg-24 Mg-25 Mg-26 Number of Protons 12 12 12 Number of Electrons 12 12 12 Mass Number 24 25 26 Number of Neutrons 12 13 14 Mass of Isotope (amu) 23.99 24.99 25.98 Percent Abundance 78.70 10.13 11.17

To determine atomic mass, calculate the contribution of each isotope to the total atomic mass by multiplying the mass of each of the isotopes by its percent abundance/ 100 and adding the results. Atomic mass = mass of isotope 1 × % abundance/ 100 isotope 1 + mass of isotope 2 × % abundance/ 100 isotope 2 + . . . Isotope Mass (amu) Abundance (%) Contribution to the Atomic Mass [latex]{}^{24}_{12}Mg[/latex] 23.99 × [latex]\frac{78.70}{100}[/latex] = 18.88 amu [latex]{}^{25}_{12}Mg[/latex] 24.99 × [latex]\frac{10.13}{100}[/latex] = 2.531 amu [latex]{}^{26}_{12}Mg[/latex] 25.98 × [latex]\frac{11.17}{100}[/latex] = [latex]\underline{2.902 amu}[/latex] Atomic mass of Mg = 24.31 amu (weighted average mass)

Question 4.9: Calculating Atomic Mass Using Table 4.7, calculate the atomi...

Chemistry an Introduction to General, Organic, and Biological Chemistry

Calculating Atomic Mass

Using Table 4.7, calculate the atomic mass for magnesium using the weighted average mass method.

Table 4.7 Isotopes of Magnesium
Atomic Symbol	${}^{24}_{12}Mg$	${}^{25}_{12}Mg$	${}^{26}_{12}Mg$
Name	Mg-24	Mg-25	Mg-26
Number of Protons	12	12	12
Number of Electrons	12	12	12
Mass Number	24	25	26
Number of Neutrons	12	13	14
Mass of Isotope (amu)	23.99	24.99	25.98
Percent Abundance	78.70	10.13	11.17

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To determine atomic mass, calculate the contribution of each isotope to the total atomic mass by multiplying the mass of each of the isotopes by its percent abundance/ 100 and adding the results. Atomic mass = mass of isotope 1 × % abundance/ 100 isotope 1 + mass of isotope 2 × % abundance/ 100 isotope 2 + . . .

Isotope	Mass (amu)		Abundance (%)		Contribution to the Atomic Mass
${}^{24}_{12}Mg$	23.99	×	$\frac{78.70}{100}$	=	18.88 amu
${}^{25}_{12}Mg$	24.99	×	$\frac{10.13}{100}$	=	2.531 amu
${}^{26}_{12}Mg$	25.98	×	$\frac{11.17}{100}$	=	$\underline{2.902 amu}$
			Atomic mass of Mg = 24.31 amu (weighted average mass)