Problem 106 - Chemistry The Molecular Science

Question

Which one of these symbols conveys more information about the atom: \({ }^{37} \mathrm{Cl}\) or \({ }_{17} \mathrm{Cl}\) ? Explain.

Step-by-Step Solution

Answer

The symbol \({ }^{37} \mathrm{Cl}\) conveys more information.

Step 1: Understand Isotope Notation

In isotope notation, the symbol \({ }^{37} \mathrm{Cl}\) represents a chlorine atom with a mass number of 37. The mass number is the sum of protons and neutrons in the nucleus.

Step 2: Analyze Atomic Notation

The symbol \({ }_{17} \mathrm{Cl}\) indicates an atomic number of 17 for chlorine. The atomic number represents the number of protons in an atom and identifies the element as chlorine.

Step 3: Compare the Information Conveyed

The isotope notation \({ }^{37} \mathrm{Cl}\) not only conveys the element (chlorine) but also provides information about the mass number (37), which can help determine the number of neutrons by subtracting the atomic number (17) from the mass number (37). On the other hand, the atomic notation \({ }_{17} \mathrm{Cl}\) only provides the atomic number.

Step 4: Determine Which Symbol Conveys More Information

By comparing the two symbols, \({ }^{37} \mathrm{Cl}\) conveys more information than \({ }_{17} \mathrm{Cl}\) because it provides both the identity of the element and additional information about the number of neutrons.

Key Concepts

Atomic Number

The atomic number is a fundamental concept in chemistry and physics, crucial for identifying the element. It is defined as the number of protons present in the nucleus of an atom. This number is unique for every element and determines its position on the periodic table. For instance, if you see the atomic number 17, you know the element is chlorine, because chlorine is the only element with 17 protons. The atomic number is always written as a subscript to the left of the element symbol, like this:

• For chlorine:
  • \(_{17} ext{Cl}\)

Using the atomic number, you can readily determine the element, as well as some of its chemical properties, since elements in the same column on the periodic table often behave similarly due to having the same number of electrons in their outer shell.
It's important to note that while the atomic number provides the identity of an atom, it does not tell you everything about the atom, such as its mass or isotopic form.

Mass Number

The mass number provides additional information about an atom beyond what the atomic number tells you. The mass number is the sum of all the protons and neutrons in an atom's nucleus. Neutrons, just like protons, reside in the nucleus and contribute significantly to its mass.
For example, if you know that the mass number of chlorine is 37, as represented in the symbol \(^{37} ext{Cl}\), it means that there are a total of 37 protons and neutrons in this particular isotope of chlorine. Since we already know chlorine has 17 protons (from its atomic number), we can calculate the number of neutrons:

• Neutrons = Mass Number - Atomic Number
  • Neutrons = 37 - 17 = 20

This additional neutron information is not specified in the atomic notation \(_{17} ext{Cl}\), which makes mass number notation more informative regarding isotopic variations of an element.
Different isotopes of the same element have the same number of protons but different numbers of neutrons, which affects their mass number.

Protons and Neutrons

Protons and neutrons are the core components of an atom's nucleus. Understanding them is essential to grasping the concept of isotopes and atomic structure.

• Protons:
  • Positively charged particles found in the nucleus.
  • The number of protons defines the atomic number and ultimately the identity of an element.
  • For chlorine, this is always 17 protons.
• Neutrons:
  • Neutral particles, meaning they have no charge.
  • They add mass to an atom and their number can vary in isotopes.
  • In the chlorine example \(^{37} ext{Cl}\), there are 20 neutrons.

The presence of neutrons affects the stability and the mass of the atom but not its chemical properties, which are determined by the protons (and, indirectly, the electrons). The number of neutrons can vary in different isotopes of the same element such as chlorine, leading to different mass numbers.