Problem 26 - Chemistry: The Central Science

Question

Fill in the gaps in the following table, assuming each column represents a neutral atom: $$ \begin{array}{|l|l|c|c|c|c|} \hline \text { Symbol } & { }^{65} \mathrm{Zn} & & & & \\ \hline \text { Protons } & & 44 & & & 92 \\ \hline \text { Neutrons } & & 57 & 49 & & \\ \hline \text { Electrons } & & & 38 & 47 & \\ \hline \text { Mass no. } & & & & 108 & 235 \\ \hline \end{array} $$

Step-by-Step Solution

Answer

The completed table is: $$ \begin{array}{|l|l|c|c|c|c|} \hline \text { Symbol } & { }^{65} \mathrm{Zn} & { }^{101} \mathrm{Ru} & { }^{87} \mathrm{Sr} & { }^{108} \mathrm{Ag} & { }^{235} \mathrm{U} \\ \hline \text { Protons } & 30 & 44 & 38 & 47 & 92 \\ \hline \text { Neutrons } & 35 & 57 & 49 & 61 & 143 \\ \hline \text { Electrons } & 30 & 44 & 38 & 47 & 92 \\ \hline \text { Mass no. } & 65 & 101 & 87 & 108 & 235 \\ \hline \end{array} $$

Step 1: Zn Atomic Number and Mass Number

The given symbol is Zn which we know is Zinc. To complete this row, we have to find the atomic number and mass number of Zinc. From the periodic table, we know that Zinc (Zn) has an atomic number of 30. The isotope given (with a mass of 65) will also have 30 protons. As the mass number (A) is given as 65, we can calculate the number of neutrons (N) as follows: N = A - Z = 65 - 30 = 35 neutrons Since the atom is neutral, the number of electrons will also be 30.

Step 2: Symbol for 44 protons

For the element with 44 protons, we look at the periodic table and find that the element with an atomic number (Z) of 44 is Ruthenium (Ru). The number of electrons is the same as the number of protons: 44 electrons. Given that the number of neutrons (N) is 57, we can calculate its mass number (A): A = Z + N = 44 + 57 = 101 Thus, this is isotope \(^{101}\mathrm{Ru}\).

Step 3: Element with 49 neutrons

In this case, we are given the number of neutrons (N=49) and electrons (e=38). To find the element's symbol, we need its atomic number (Z). As the atom is neutral, we know Z is equal to the number of electrons: Z = e = 38 From the periodic table, we find that the element with an atomic number of 38 is Strontium (Sr). Now, we can find the mass number (A): A = Z + N = 38 + 49 = 87 Thus, this is isotope \(^{87}\mathrm{Sr}\).

Step 4: Element with 47 electrons

We are given the number of electrons (e=47) and the mass number (A=108). Again, we know that the number of protons (Z) is the same as the number of electrons: Z = e = 47 The element with an atomic number of 47 is Silver (Ag). Now, we can calculate the number of neutrons (N): N = A - Z = 108 - 47 = 61 Thus, this is isotope \(^{108}\mathrm{Ag}\).

Step 5: Element with 92 protons

For the element with 92 protons, we look at the periodic table and find that the element with an atomic number (Z) of 92 is Uranium (U). The number of electrons is the same as the number of protons: 92 electrons. Given that the mass number (A) is 235, we can calculate its number of neutrons (N): N = A - Z = 235 - 92 = 143 Thus, this is isotope \(^{235}\mathrm{U}\). The completed table is: $$ \begin{array}{|l|l|c|c|c|c|} \hline \text { Symbol } & { }^{65} \mathrm{Zn} & { }^{101} \mathrm{Ru} & { }^{87} \mathrm{Sr} & { }^{108} \mathrm{Ag} & { }^{235} \mathrm{U} \\ \hline \text { Protons } & 30 & 44 & 38 & 47 & 92 \\ \hline \text { Neutrons } & 35 & 57 & 49 & 61 & 143 \\ \hline \text { Electrons } & 30 & 44 & 38 & 47 & 92 \\ \hline \text { Mass no. } & 65 & 101 & 87 & 108 & 235 \\ \hline \end{array} $$

Key Concepts

Neutral Atom Properties

Every neutral atom is distinctive, comprised of a nucleus surrounded by electrons. The nucleus contains two types of subatomic particles – neutrons and protons, which together account for nearly all of an atom's mass. Electrons, which are far less massive, orbit the nucleus and determine the atom's size.

For an atom to be neutral, the number of protons (positively charged) must equal the number of electrons (negatively charged), as their charges cancel each other out. For instance, Zinc (Zn) has 30 protons, thus a neutral Zn atom will also house 30 electrons. The neutrality of these atoms plays a crucial role in chemical reactions and bonding.

Isotopes

Isotopes are variants of the same chemical element, each possessing identical numbers of protons but differing in neutron count. This difference in neutron number imparts distinct mass numbers to the isotopes, which is the sum of protons and neutrons in the nucleus. Radioactive isotopes, or radioisotopes, sometimes occur naturally or can be created artificially.

An example is Uranium, which has isotopes like Uranium-235 with 143 neutrons, and others like Uranium-238 with more neutrons. Isotopes have the same chemical behavior but can vary greatly in physical properties, such as stability and half-life.

Atomic Number

The atomic number, designated as 'Z', is a fundamental characteristic that defines each element. It corresponds to the number of protons present in the nucleus of an atom. Since the electric charge of protons dictates an atom's identity, the atomic number is essentially the element's unique identifier on the periodic table. For instance, Carbon has an atomic number of 6, meaning every atom of Carbon has 6 protons. No two different elements share the same atomic number, ensuring distinctiveness among the elements.

Mass Number

Mass number, written as 'A', is the total number of protons and neutrons in the atom's nucleus. It's important to note that mass number is not the same as atomic weight; the latter is an average that takes into account the various isotopes and their abundance. Mass number is always an integer. As per our array, Silver (Ag) has an atomic number of 47. With a mass number of 108, it has 61 neutrons (since 108 - 47 = 61). It's critical when determining the specific isotope of an element.

Periodic Table

The periodic table is an orchestrated display of chemical elements, structured by increasing atomic number. It showcases the periodic trends and the relationships between the properties of elements. For example, elements in the same column (or group) usually have similar chemical behaviors. The table also separates metals from nonmetals and can indicate the likelihood of an element forming certain types of ions.

Students and chemists use the periodic table as a fundamental reference to understand the relationships between the various elements and to predict the properties and behaviors of unknown compounds.