Problem 6 - Campbell Biology

Question

We can represent atoms by listing the number of protons, neutrons, and electrons-for example, \(2 p^{+}, 2 n^{0}, 2 e^{-}\) for helium. Which of the following represents the \({ }^{18} \mathrm{O}\) isotope of oxygen? (A) \(7 p^{+}, 2 n^{0}, 9 e^{-}\) (B) \(8 p^{+}, 10 n^{0}, 8 e^{-}\) (C) \(9 p^{+}, 9 n^{0}, 9 e^{-}\) (D) \(10 p^{+}, 8 n^{0}, 9 e^{-}\)

Step-by-Step Solution

Answer

Option (B) is correct: \(8 p^{+}, 10 n^{0}, 8 e^{-}\).

Step 1: Understand the Notation

The notation \({ }^{18} \mathrm{O}\) represents an isotope of oxygen. The number 18 represents the mass number, which is the total number of protons and neutrons in the nucleus.

Step 2: Identify Protons in Oxygen

Oxygen has an atomic number of 8, which means it has 8 protons \(8 p^{+}\). This number does not change between isotopes.

Step 3: Calculate the Number of Neutrons

In the isotope \({ }^{18} \mathrm{O}\), the mass number is 18. Since the number of protons is 8, the number of neutrons is \text{mass number} - \text{number of protons} = 18 - 8 = 10\ n^{0}.

Step 4: Identify the Electrons

For a neutral atom, the number of electrons is equal to the number of protons. Therefore, \({ }^{18} \mathrm{O}\) has 8 electrons \(8 e^{-}\).

Step 5: Compare with Given Options

Now compare the calculated values (8 protons, 10 neutrons, and 8 electrons) with the options given:(A) \(7 p^{+}, 2 n^{0}, 9 e^{-}\) \rightarrow Incorrect(B) \(8 p^{+}, 10 n^{0}, 8 e^{-}\) \rightarrow Correct(C) \(9 p^{+}, 9 n^{0}, 9 e^{-}\) \rightarrow Incorrect(D) \(10 p^{+}, 8 n^{0}, 9 e^{-}\) \rightarrow Incorrect

Key Concepts

Atomic Structure

Atomic structure refers to the arrangement of three main subatomic particles within an atom: protons, neutrons, and electrons. Protons and neutrons are found in the nucleus at the center of the atom, while electrons orbit the nucleus in various energy levels. Understanding the atomic structure is essential as it determines the element's identity and properties. Each element in the periodic table has a unique number of protons, known as the atomic number, which determines the element's identity. Electrons play a crucial role in chemical reactions and bonding, while the number of neutrons can vary among atoms of the same element, leading to different isotopes. To illustrate: the nucleus contains positive protons and neutral neutrons, tightly bound together, while negatively charged electrons move around this nucleus. This arrangement ensures that the overall charge of an atom is balanced or neutral in its natural state.

Neutrons

Neutrons are one of the three fundamental subatomic particles found in an atom. They are uncharged (neutral) particles located in the nucleus alongside protons. Despite lacking an electric charge, neutrons play a critical role in the stability of the nucleus. Together with protons, neutrons contribute to the mass number of an atom, which is the sum of protons and neutrons present in the nucleus. The number of neutrons in an atom can vary, resulting in different isotopes of the same element. For instance, the isotope \({ }^{18} \mathrm{O}\) of oxygen has 8 protons and 10 neutrons, leading to a mass number of 18. Neutron numbers can influence both the stability and radioactive nature of an isotope. The mass number of an isotope is crucial in distinguishing it from other isotopes of the same element.

Atomic Number

The atomic number of an element is the number of protons found in the nucleus of its atoms. It is a fundamental property that defines each element on the periodic table. For example, oxygen has an atomic number of 8, meaning every oxygen atom possesses 8 protons. The atomic number is a unique identifier for elements and does not change among different isotopes of the same element. In other words, all oxygen isotopes, whether \({ }^{16} \mathrm{O}\), \({ }^{17} \mathrm{O}\), or \({ }^{18} \mathrm{O}\), will always have 8 protons. This is a principal concept for students to grasp because it ensures the consistency and predictability of chemical reactions and properties within elements. Knowing the atomic number also allows us to determine the number of electrons in a neutral atom, since the number of electrons equals the number of protons.