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Chapter 2: Problem 21

(a) Define atomic number and mass number. (b) Which of these can vary without changing the identity of the element?

Short Answer

Expert verified
(a) The atomic number (Z) is the number of protons in an atom's nucleus and determines the element's chemical properties. The mass number (A) is the sum of protons and neutrons in the nucleus, representing the atomic mass in amu. (b) The mass number can vary without changing the element's identity since isotopes of the same element have different mass numbers but still maintain the same chemical properties and remain the same element.

Step by step solution

01

(a) Define Atomic Number and Mass Number

The atomic number (Z) of an element is the number of protons in the nucleus of an atom. It determines the element's chemical properties and its position in the periodic table. Every element has a unique atomic number. The mass number (A) of an atom is the sum of protons and neutrons in the nucleus. It represents the atomic mass of an atom, measured in atomic mass units (amu). The mass number is not unique for an element, as isotopes of the same element can have different mass numbers due to varying numbers of neutrons.
02

(b) Determine Which Characteristic Can Vary Without Changing the Identity of the Element

The identity of an element is determined by its atomic number because the atomic number defines the number of protons present in the atom, which in turn determines the element's chemical properties. Therefore, the mass number can vary without changing the identity of the element. Isotopes are atoms of the same element that have the same atomic number but different mass numbers because they have varying numbers of neutrons. These isotopes still maintain the same chemical properties and remain the same element, proving that the mass number can vary without changing the identity of an element.

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Most popular questions from this chapter

Mass spectrometry is more often applied to molecules than to atoms. We will see in Chapter 3 that the molecular weight of a molecule is the sum of the atomic weights of the atoms in the molecule. The mass spectrum of \(\mathrm{H}_{2}\) is taken under conditions that prevent decomposition into \(\mathrm{H}\) atoms. The two naturally occurring isotopes of hydrogen are \({ }^{1} \mathrm{H}\) (atomic mass = 1.00783 amu; abundance \(99.9885 \%\) ) and \({ }^{2} \mathrm{H}\) (atomic mass \(=\) 2.01410 amu; abundance \(0.0115 \%\) ). (a) How many peaks will the mass spectrum have? (b) Give the relative atomic masses of each of these peaks. (c) Which peak will be the largest and which the smallest?

Give the names and charges of the cation and anion in each of the following compounds: (a) \(\mathrm{CuS},(\mathbf{b}) \mathrm{Ag}_{2} \mathrm{SO}_{4}\), (c) \(\mathrm{Al}\left(\mathrm{ClO}_{3}\right)_{3},\) (d) \(\mathrm{Co}(\mathrm{OH})_{2}\), (e) \(\mathrm{PbCO}_{3}\).

One way in which Earth's evolution as a planet can be understood is by measuring the amounts of certain isotopes in rocks. One quantity recently measured is the ratio of \({ }^{129} \mathrm{Xe}\) to \({ }^{130}\) Xe in some minerals. In what way do these two isotopes differ from one another? In what respects are they the same?

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How many hydrogen atoms are in each of the following: (a) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH},\) (b) \(\mathrm{Ca}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2},\) (c) \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4} ?\)
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