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Chapter 2: Problem 89

For the noble gases (the Group 8 A elements), \({ }_{2}^{4} \mathrm{He}\), \({ }_{10}^{20} \mathrm{Ne},{ }_{18}^{40} \mathrm{Ar},{ }_{36}^{84} \mathrm{Kr},\) and \({ }_{54}^{132} \mathrm{Xe},\) (a) determine the number of protons and neutrons in the nucleus of each atom, and (b) determine the ratio of neutrons to protons in the nucleus of each atom. Describe any general trend you discover in the way this ratio changes with increasing atomic number.

Short Answer

Expert verified
Number of protons for He, Ne, Ar, Kr, and Xe are 2, 10, 18, 36, and 54 respectively. Number of neutrons for He, Ne, Ar, Kr, and Xe are 2, 10, 22, 48, and 78 respectively. The ratios of neutrons to protons for He, Ne, Ar, Kr, and Xe are 1.00, 1.00, 1.22, 1.33, and 1.44 respectively. The ratio increases with the increasing atomic number, which means that as we move down the group, the number of neutrons increases at a faster rate than protons.

Step by step solution

01

Identify Protons

The atomic number of an atom, which is the lower number in the atomic notation, tells us the number of protons. So, for the given noble gases, the number of protons for Helium (He) is 2, for Neon (Ne) is 10, for Argon (Ar) is 18, for Krypton (Kr) is 36, and for Xenon (Xe) is 54.
02

Identify Neutrons

The number of neutrons can be obtained by subtracting the atomic number (number of protons) from the atomic mass (number at the top in atomic notation). So, the number of neutrons for He is \(4-2=2\), for Ne is \(20-10=10\), for Ar is \(40-18=22\), for Kr is \(84-36=48\), and for Xe is \(132-54=78\).
03

Compute Ratio

To find the ratio of the number of neutrons to the number of protons, divide the number of neutrons by the number of protons for each atom. Resulting ratios are: for He \(2/2=1.00\), for Ne \(10/10=1.00\), for Ar \(22/18=1.22\), for Kr \(48/36=1.33\), and for Xe \(78/54=1.44\).
04

Identify Trend

Looking at the increasing atomic numbers, there's a trend where the ratio of the number of neutrons to protons for these noble gases increases, which indicates that as the atomic number increases, the number of neutrons increases at a faster rate than protons in the nucleus of the atom.

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Most popular questions from this chapter

Consult a handbook of chemical and physical data (ask your instructor where you can locate a copy of the handbook) to find (a) two metals less dense than water, (b) two metals more dense than mercury, (c) the densest known solid metallic element, (d) the densest known solid nonmetallic element.

Describe the changes in properties (from metals to nonmetals or from nonmetals to metals) as we move (a) down a periodic group and (b) across the periodic table from left to right.

Sulfur (S) and fluorine (F) form several different compounds. One of them, \(\mathrm{SF}_{6},\) contains \(3.55 \mathrm{~g}\) of \(\mathrm{F}\) for every gram of S. Use the law of multiple proportions to determine \(n,\) which represents the number of \(\mathrm{F}\) atoms in \(\mathrm{SF}_{n}\), given that it contains \(2.37 \mathrm{~g}\) of \(\mathrm{F}\) for every gram of \(\mathrm{S}\).

Describe the two commonly used molecular models.

The Group \(1 \mathrm{~B}\) metals, \(\mathrm{Cu}, \mathrm{Ag},\) and \(\mathrm{Au},\) are called coinage metals. What chemical properties make them specially suitable for making coins and jewelry?
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