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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

Determine whether each of the following statements is true or false. If false, correct the statement to make it true: (a) The nucleus has most of the mass and comprises most of the volume of an atom. (b) Every atom of a given element has the same number of protons. (c) The number of electrons in an atom equals the number of neutrons in the atom. (d) The protons in the nucleus of the helium atom are held together by a force called the strong nuclear force.

(a) What isotope is used as the standard in establishing the atomic mass scale? (b) The atomic weight of boron is reported as 10.81 , yet no atom of boron has the mass of 10.81 amu. Explain.

Complete the table by filling in the formula for the ionic compound formed by each pair of cations and anions, as shown for the first pair. $$ \begin{array}{|l|c|c|c|c|} \hline \text { Ion } & \mathrm{K}^{+} & \mathrm{NH}_{4}^{+} & \mathrm{Mg}^{2+} & \mathrm{Fe}^{3+} \\ \hline \mathrm{Cl}^{-} & \mathrm{KCl} & & & \\ \hline \mathrm{OH}^{-} & & & & \\ \hline \mathrm{CO}_{3}^{2-} & & & & \\ \hline \mathrm{PO}_{4}{ }^{3-} & & & & \\ \hline \end{array} $$

From the following list of elements \(-\mathrm{Ar}, \mathrm{H}, \mathrm{Ga}, \mathrm{Al}, \mathrm{Ca}, \mathrm{Br}, \mathrm{Ge},\) \(\mathrm{K}, \mathrm{O}\) - pick the one that best fits each description. Use each element only once: (a) an alkali metal, (b) an alkaline earth metal, \((\mathbf{c})\) a noble gas, \((\mathbf{d})\) a halogen, \((\mathbf{e})\) a metalloid, \((\mathbf{f})\) a nonmetal listed in group \(1 \mathrm{~A},(\mathrm{~g})\) a metal that forms a \(3+\) ion, \((\mathbf{h})\) a nonmetal that forms a \(2-\) ion, (i) an element that resembles aluminum.

An atom of rhodium (Rh) has a diameter of about \(2.7 \times 10^{-8} \mathrm{~cm}\). (a) What is the radius of a rhodium atom in angstroms \((\AA)\) and in meters \((\mathrm{m}) ?(\mathbf{b})\) How many \(\mathrm{Rh}\) atoms would have to be placed side by side to span a distance of \(6.0 \mu \mathrm{m} ?\) (c) If you assume that the \(\mathrm{Rh}\) atom is a sphere, what is the volume in \(\mathrm{m}^{3}\) of a single atom?
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