Explain what is supposed by the atomic mass of an element. Calculate the atomic mass of an aspect from the masses and also loved one percenteras of the isotopes of the element.

You are watching: Atomic mass of boron 10 and 11


In jiyuushikan.orgisattempt we very rarely address just one isotope of an aspect. We usage a mixture of the isotopes of an aspect in jiyuushikan.orgical reactions and also various other elements of jiyuushikan.orgisattempt, bereason all of the isotopes of an aspect react in the exact same manner. That means that we seldom need to worry about the mass of a particular isotope, however rather we have to understand the average mass of the atoms of an facet. Using the masses of the various isotopes and exactly how plentiful each isotope is, we can discover the average mass of the atoms of an element. The atomic mass of an facet is the weighted average mass of the atoms in a normally developing sample of the element. Atomic mass is frequently reported in atomic mass units.


Calculating Atomic Mass

You have the right to calculate the atomic mass (or average mass) of an aspect offered you understand the relative abundance(the fraction of an facet that is a provided isotope), the element"s naturally occurring isotopes, and the masses of those different isotopes. We deserve to calculate this by the following equation:

< extAtomic mass = left( \%_1 ight) left( extmass_1 ight) + left( \%_2 ight) left( extmass_2 ight) + cdots>

Look carefully to watch just how this equation is supplied in the complying with examples.


Example (PageIndex1): Boron Isotopes

Boron has two normally developing isotopes. In a sample of boron, (20\%) of the atoms are (ceB)-10, which is an isotope of boron through 5 neutrons and mass of (10 : extamu). The various other (80\%) of the atoms are (ceB)-11, which is an isotope of boron with 6 neutrons and also a mass of (11 : extamu). What is the atomic mass of boron?

Solution

Boron has 2 isotopes. We will certainly use the equation:

< extAtomic mass = left( \%_1 ight) left( extmass_1 ight) + left( \%_2 ight) left( extmass_2 ight) + cdots onumber>

Isotope 1: (\%_1 = 0.20) (Write all percentperiods as decimals), ( extmass_1 = 10) Isotope 2: (\%_2 = 0.80), ( extmass_2 = 11)

Substitute these right into the equation, and also we get:

< extAtomic mass = left( 0.20 ight) left( 10 ight) + left( 0.80 ight) left( 11 ight) onumber>

< extAtomic mass = 10.8 : extamu onumber>

The mass of an average boron atom, and also for this reason boron"s atomic mass, is (10.8 : extamu).


Example (PageIndex2): Neon Isotopes

Neon has actually three normally developing isotopes. In a sample of neon, (90.92\%) of the atoms are (ceNe)-20, which is an isotope of neon via 10 neutrons and a mass of (19.99 : extamu). Anvarious other (0.3\%) of the atoms are (ceNe)-21, which is an isotope of neon via 11 neutrons and a mass of (20.99 : extamu). The final (8.85\%) of the atoms are (ceNe)-22, which is an isotope of neon with 12 neutrons and also a mass of (21.99 : extamu). What is the atomic mass of neon?

Solution

Neon has actually three isotopes. We will usage the equation:

< extAtomic mass = left( \%_1 ight) left( extmass_1 ight) + left( \%_2 ight) left( extmass_2 ight) + cdots onumber>

Isotope 1: (\%_1 = 0.9092) (compose all percentperiods as decimals), ( extmass_1 = 19.99) Isotope 2: (\%_2 = 0.003), ( extmass_2 = 20.99) Isotope 3: (\%_3 = 0.0885), ( extmass_3 = 21.99)

Substitute these into the equation, and we get:

< extAtomic mass = left( 0.9092 ight) left( 19.99 ight) + left( 0.003 ight) left( 20.99 ight) + left( 0.0885 ight) left( 21.99 ight) onumber>

< extAtomic mass = 20.17 : extamu onumber>

The mass of an average neon atom is (20.17 : extamu)


The routine table offers the atomic mass of each aspect. The atomic mass is a number that usually shows up below the element"s symbol in each square. Notice that the atomic mass of boron (symbol (ceB)) is 10.8, which is what we calculated in Example (PageIndex1), and also the atomic mass of neon (symbol (ceNe)) is 20.8, which is what we calculated in Example (PageIndex2). Take time to notice that not all periodic tables have actually the atomic number over the element"s symbol and also the mass number below it. If you are ever confused, remember that the atomic number need to constantly be the smaller sized of the 2 and will be a totality number, while the atomic mass have to always be the larger of the 2 and also will certainly be a decimal number.


Exercise (PageIndex1)

Chlorine has two normally emerging isotopes. In a sample of chlorine, (75.77\%) of the atoms are (ceCl)-35, with a mass of (34.97 : extamu). Another (24.23\%) of the atoms are (ceCl)-37, via a mass of (36.97 : extamu). What is the atomic mass of chlorine?

Answer 35.45 amu

Summary

An element"s atomic mass is the weighted average of the masses of the isotopes of an aspect An element"s atomic mass can be calculated offered the relative abundanceof the element"s naturally developing isotopes and the masses of those isotopes are known. The regular table is a convenient way to summarize indevelopment around the various aspects. In addition to the element"s symbol, many routine tables will certainly likewise contain the element"s atomic number and the element"s atomic mass.

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