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Ch.2 - Atoms, Molecules, and Ions
Chapter 2, Problem 92a

Identify the element represented by each of the following symbols and give the number of protons and neutrons in each: (a) 7433X

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Atomic Number

The atomic number of an element is the number of protons found in the nucleus of an atom. It uniquely identifies an element and determines its position on the periodic table. In the notation <sup>74</sup><sub>33</sub>X, the subscript '33' represents the atomic number, indicating that the element has 33 protons.
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Guided course
02:10
Atom Structure

Mass Number

The mass number of an atom is the total number of protons and neutrons in its nucleus. It is represented by the superscript in the notation <sup>74</sup><sub>33</sub>X, where '74' is the mass number. To find the number of neutrons, subtract the atomic number from the mass number: neutrons = mass number - atomic number.
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Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons. This results in different mass numbers for the isotopes of the same element. In the case of <sup>74</sup><sub>33</sub>X, knowing the mass number allows us to identify the specific isotope of the element with atomic number 33, which is arsenic.
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Related Practice
Textbook Question
Very small semiconductor crystals, composed of approximately 1000 to 10,000 atoms, are called quantum dots. Quantum dots made of the semiconductor CdSe are now being used in electronic reader and tablet displays because they emit light efficiently and in multiple colors, depending on dot size. The density of CdSe is 5.82 g/cm3. (b) CdSe quantum dots that are 2.5 nm in diameter emit blue light upon stimulation. Assuming that the dot is a perfect sphere and that the empty space in the dot can be neglected, calculate how many Cd atoms are in one quantum dot of this size.
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Textbook Question

(a) Assuming the dimensions of the nucleus and atom shown in Figure 2.10, what fraction of the volume of the atom is taken up by the nucleus?

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Textbook Question

(b) Using the mass of the proton from Table 2.1 and assuming its diameter is 1.0 * 10-15 m, calculate the density of a proton in g>cm3.

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Textbook Question

Identify the element represented by each of the following symbols and give the number of protons and neutrons in each: (b) 12753X

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Textbook Question

The nucleus of 6Li is a powerful absorber of neutrons. It exists in the naturally occurring metal to the extent of 7.5%. In the era of nuclear deterrence, large quantities of lithium were processed to remove 6Li for use in hydrogen bomb production. The lithium metal remaining after removal of 6Li was sold on the market. (b) The atomic masses of 6Li and 7Li are 6.015122 and 7.016004 u, respectively. A sample of lithium depleted in the lighter isotope was found on analysis to contain 1.442% 6Li. What is the average atomic weight of this sample of the metal?

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Textbook Question

The element argon has three naturally occurring isotopes, with 18, 20, and 22 neutrons in the nucleus, respectively. (a) Write the full chemical symbols for these three isotopes.

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