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Chapter 2: Problem 34

(a) What is the mass in amu of a carbon-12 atom? (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?

Short Answer

Expert verified
(a) The mass of a carbon-12 atom is 12 amu because the atomic mass unit (amu) is defined as one-twelfth the mass of a carbon-12 atom. (b) The atomic weight of carbon is reported as 12.011 because it is a weighted average of the masses of its naturally occurring isotopes (carbon-12 and carbon-13), taking into account their natural abundance in the environment.

Step by step solution

01

Define atomic mass unit and carbon-12 atom

An atomic mass unit (amu) is defined as one-twelfth the mass of a carbon-12 atom. The carbon-12 atom is an isotope of carbon, which has 6 protons, 6 electrons, and 6 neutrons. The existence of isotopes means that elements can have the same number of protons (defining their atomic number) but with different numbers of neutrons, giving them slightly different atomic masses.
02

Find the mass of a carbon-12 atom in amu

Since an atomic mass unit (amu) is defined as one-twelfth the mass of a carbon-12 atom, the mass of a carbon-12 atom is exactly 12 amu by definition. Answer to (a): The mass of a carbon-12 atom is 12 amu.
03

Discuss isotopes and atomic weight calculation

The atomic weight of an element is the weighted average of the masses of all the naturally occurring isotopes of the element. This means that all the isotopes of that element have a specific contribution to the atomic weight considering their abundance in nature. Carbon has two isotopes: carbon-12 (with 6 neutrons) and carbon-13 (with 7 neutrons).
04

Explain the reason for atomic weight deviation

The atomic weight of carbon is reported as 12.011 rather than an exact 12 due to the presence of the carbon-13 isotope. The atomic weight is slightly higher than 12 because carbon-13 is heavier than carbon-12 (having an additional neutron) and carbon-13 has a natural abundance in the environment. Answer to (b): The atomic weight of carbon is reported as 12.011 because it is a weighted average of the masses of its naturally occurring isotopes (carbon-12 and carbon-13) and takes into account their natural abundance in the environment.

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Most popular questions from this chapter

Elements in the same group of the periodic table often form oxyanions with the same general formula. The anions are also named in a similar fashion. Based on these observations,suggest a chemical formula or name, as appropriate, for each of the following ions:\((\mathbf{a}) \mathrm{BrO}_{4}^{-},(\mathbf{b}) \mathrm{SeO}_{3}^{2-}\) \((\mathbf{c})\) arsenate ion, \((\mathbf{d})\) hydrogen tellurate ion.

How many protons, neutrons, and electrons are in the following atoms? (a) \(^{40} \mathrm{Ar},(\mathbf{b})^{65} \mathrm{Zn},(\mathbf{c})^{70} \mathrm{Ga},(\mathbf{d})^{80} \mathrm{Br},(\mathbf{e})^{184} \mathrm{W}\) \((\mathbf{f})^{243} \mathrm{Am} .\)

(a) What is meant by the term isomer? (b) Among the four alkanes, ethane, propane, butane, and pentane, which is capable of existing in isomeric forms?

How many of the indicated atoms are represented by each chemical formula: (a) carbon atoms in \(\mathrm{C}_{4} \mathrm{H}_{9} \mathrm{COOCH}_{3}\) (b) oxygen atoms in \(\mathrm{Ca}\left(\mathrm{ClO}_{3}\right)_{2},(\mathbf{c})\) hydrogen atoms in \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{HPO}_{4} ?\)

Chloropropane is derived from propane by substituting Cl for \(\mathrm{H}\) on one of the carbon atoms. (a) Draw the structural formulas for the two isomers of chloropropane. (b) Suggest names for these two compounds.
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