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Chapter 2: Problem 25

(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, determining its position in the periodic table and its identity. The mass number (A) is the total number of protons and neutrons in the nucleus. (b) The mass number can vary without changing the element's identity, as different isotopes have varying numbers of neutrons but the same number of protons (atomic number).

Step by step solution

01

Define Atomic Number

The atomic number, often represented by the symbol \(Z\), is the number of protons in the nucleus of an atom. The atomic number is a unique property of an element and is used to define its position in the periodic table. Each element has a specific number of protons, and therefore, a specific atomic number. For example, hydrogen has an atomic number of 1, which means it has one proton in its nucleus.
02

Define Mass Number

The mass number, often represented by the symbol \(A\), is the total number of protons and neutrons in the nucleus of an atom. The mass number does not include electrons, as their mass is negligible compared to the mass of protons and neutrons. The mass number is not unique for a specific element, as the number of neutrons can vary for atoms of the same element (known as isotopes).
03

Determine Which Can Vary Without Changing the Element's Identity

As we defined in the previous steps, the atomic number is directly related to the number of protons, which determines the element's identity. In contrast, the mass number is related to the total number of protons and neutrons. Since the number of neutrons can vary and create different isotopes of the same element, the mass number can change without impacting the element's identity. However, changing the atomic number would result in a different element due to a change in the number of protons. So, the mass number can vary without changing the identity of the element.

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Most popular questions from this chapter

Rubidium has two naturally occurring isotopes, rubidium-85 (atomic mass \(=84.9118\) amu; abundance \(=72.15 \%\) ) and rubidium-87 (atomic mass = 86.9092 amu; abundance = 27.85\(\%\) ). Calculate the atomic weight of rubidium.

Write the chemical formula for each substance mentioned in the following word descriptions (use the front inside cover to find the symbols for the elements you do not know). (a) Zinc carbonate can be heated to form zinc oxide and carbon dioxide. (b) On treatment with hydrofluoric acid, silicon dioxide forms silicon tetrafluoride and water. (c) Sulfur dioxide reacts with water to form sulfurous acid. (d) The substance phosphorus trihydride, commonly called phosphine, is a toxic gas. (e) Perchloric acid reacts with cadmium to form cadmium(II) perchlorate. (f) Vanadium(II) bromide is a colored solid.

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

Provide the name or chemical formula, as appropriate, for each of the following acids: (a) hydroiodic acid, (b) chloric acid, (c) nitrous acid, acid, \((\mathbf{d}) \mathrm{H}_{2} \mathrm{CO}_{3},(\mathbf{e}) \mathrm{HClO}_{4},(\mathbf{f}) \mathrm{CH}_{3} \mathrm{COOH}\)

Because many ions and compounds have very similar names, there is great potential for confusing them. Write the correct chemical formulas to distinguish between \((\mathbf{a})\) calcium sulfide and calcium hydrogen sulfide, \((\mathbf{b})\) hydrobromic acid and bromic acid \((\mathbf{c})\) aluminum nitride and aluminum nitrite,\((\mathbf{d})\)iron(II) oxide and iron(III) oxide,\((\mathbf{e})\)ammonia and ammonium ion, \((\mathbf{f})\)potassium sulfite and potassium bisulfite,\((\mathbf{g})\) mercurous chloride and mercuric chloride, \((\mathbf{h})\) chloric acid and perchloric acid.
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