Question

One isotope of a nonmetallic element has mass number 31 and 16 neutrons in the nucleus. The anion derived from the isotope has 18 electrons. Write the chemical symbol for this anion.

Short answer

The chemical symbol is \(\text{P}^{3-}\).

Step-by-step solution

Determine the Number of Protons

The mass number of the isotope is 31, which is the sum of the protons and neutrons. Since there are 16 neutrons, the number of protons, which is also the atomic number, is calculated as follows: \[ \text{Number of protons} = 31 - 16 = 15 \].

Identify the Element

The atomic number identifies the element. We use the periodic table to find that an element with 15 protons is phosphorus (P).

Calculate the Anion Charge

The anion derived from this isotope has 18 electrons. Since neutral phosphorus has 15 electrons (equal to the number of protons), the anion has 3 extra electrons. Thus, the charge of the anion is \(-3\).

Write the Chemical Symbol

The chemical symbol for the phosphorus anion with a \(-3\) charge is \(\text{P}^{3-}\).

Key concepts

Isotope

An isotope refers to different forms of the same element that have the same number of protons, but different numbers of neutrons in their nuclei. This results in isotopes having different mass numbers even though they are the same element.
For example, in our original problem, the isotope of the nonmetallic element in question has a mass number of 31 and 16 neutrons. This means that despite having multiple isotopes, the element can still be identified by its specific number of neutrons in combination with its mass number.
Isotopes are important in various fields, including chemistry and physics, because they help in understanding the properties and behaviors of elements as well as their stability. It also plays a significant role in medical imaging and treatment.

Mass Number

The mass number of an element is the sum of the protons and neutrons present in its atomic nucleus. This number gives us important information about the isotope of the element.
In our example, the isotope has a mass number of 31, meaning there are 31 combined protons and neutrons. Since we know there are 16 neutrons, it allows us to calculate the number of protons by subtracting the number of neutrons from the mass number (31 - 16 = 15 protons).
Understanding the mass number is crucial as it helps in identifying the specific isotope of an element and distinguishes it from other isotopes of the same atom, which might have different neutron numbers.

Protons

Protons are positively charged particles found in the nucleus of an atom. They are a fundamental part of an atom's identity, as the number of protons determines the element's atomic number.
In the case of this exercise, the element has 15 protons. By referring to the periodic table, we can match this atomic number to an element, which is phosphorus (P). The atomic number for an element can never change without changing the element itself, as it defines what the element actually is.
Protons are essential not only in defining the identity of the element but also contributing to its mass number along with neutrons.

Neutrons

Neutrons are neutral particles located within the atomic nucleus alongside protons. They do not possess any electric charge, but they contribute significantly to the mass of an atom.
In our specific example, the isotope has 16 neutrons. These neutrons help add to the mass number of 31, but do not affect the overall charge of the atom. Neutrons are crucial for the stability of the nucleus as they help to mediate the strong force between protons, which are positively charged and naturally repel each other.
The number of neutrons can vary even in the same element, which results in different isotopes. Thus, they are key in determining the particular isotope of an element.

Anion

An anion is a negatively charged ion formed when an atom gains one or more electrons. This results in more electrons than protons, giving the ion a negative charge.
In the situation described, the phosphorus atom gains three electrons to become an anion with 18 electrons total, while it has only 15 protons. This situation gives the phosphorus anion a charge of (-3), as it has three more electrons than protons.

• Anions are critical in various chemical and biological processes, such as conductivity in solutions, and formation of salts.
• They are represented by adding a superscript to the element’s chemical symbol indicating their charge, e.g., (P^{3-}) for the example in this exercise.

Understanding anions and how they form aids in grasping concepts of ionic bonding and compound formation.