Question

Does the following drawing represent a neutral atom or an ion? Write its complete chemical symbol including mass number, atomic number, and net charge (if any). [Sections \(2.3\) and \(2.7]\)

Short answer

This drawing represents an ion, not a neutral atom, since it has 16 protons and 18 electrons. The element is sulfur (S) with atomic number 16. The mass number is 32 (16 protons + 16 neutrons). The net charge is -2 (16 protons - 18 electrons). So, the complete chemical symbol is \(_{16}^{32}\text{S}^{-2}\).

Step-by-step solution

Determine if the element is neutral or an ion

We are given 16 protons and 18 electrons. Since the number of protons is not equal to the number of electrons, this element is an ion, not a neutral atom.

Identify the element

Using the atomic number (number of protons), which is 16, we can identify the element. Looking at the periodic table, we find that the element with atomic number 16 is sulfur (S).

Calculate the mass number

We are given 16 neutrons. The mass number is the sum of protons and neutrons. Therefore, the mass number of this element is \(16 + 16 = 32\).

Determine the net charge

Now we need to find the net charge of the ion. The net charge is determined by the difference in the number of protons and electrons. In this case, there are 16 protons and 18 electrons, so the net charge is \(16 - 18 = - 2\). This means the element has a -2 charge.

Write the complete chemical symbol

Now that we have gathered all the information needed, we can write the complete chemical symbol for the ion. The symbol includes the element symbol (S), the atomic number (16), the mass number (32), and the net charge (-2). We write the atomic number as a subscript to the left of the element symbol, the mass number as a superscript to the left of the element symbol, and the net charge as a superscript to the right of the element symbol. So the complete chemical symbol for the ion is: \(\hspace{2mm}_{}^{32}\text{S}_{16}^{-2}\)

Key concepts

Atomic Number

The atomic number is a fundamental property of an element, representing the number of protons in the nucleus of an atom. Each element on the periodic table is uniquely defined by its atomic number. For example, a sulfur atom always has an atomic number of 16, which signifies it has 16 protons. Understanding the atomic number is crucial because it not only determines the identity of the element but also its position on the periodic table.

In chemical symbols, the atomic number is denoted as a subscript to the left of the element's symbol. For instance, sulfur with an atomic number of 16 is represented as \( \_{}^{ }\text{S}_{16} \). The importance of the atomic number can also be seen in how it specifically distinguishes ions and neutral atoms. For a neutral atom, the number of protons (atomic number) equals the number of electrons, maintaining a balanced charge.

Mass Number

The mass number of an atom is calculated by the sum of the number of protons and neutrons in its nucleus. It provides an approximation of the atomic mass, which is relevant for understanding isotopes and nuclear stability. While the atomic number is the same for all atoms of an element, the mass number can vary depending on the number of neutrons.

In the representation of chemical symbols, the mass number is indicated as a superscript to the left of the element's symbol. For the ion in our example, the sulfur atom has a mass number calculated by adding together its 16 protons and 16 neutrons, giving us \( \_{}^{32}\text{S}_{ } \). This information helps scientists and students alike understand the specific isotope of an element they are dealing with.

Net Charge

Net charge refers to the overall electrical charge of an atom or molecule, which is the total charge after accounting for all of the protons (positive charges) and electrons (negative charges). If there are more electrons than protons, the net charge will be negative, indicating an anion. Conversely, if there are more protons than electrons, the net charge is positive, indicating a cation.

In chemical notation, the net charge is displayed as a superscript to the right of the element's symbol. In our exercise example, the ion has two more electrons than protons, giving it a net charge of -2. This is represented as \(\text{S}^{-2}\). Understanding net charge is essential for predicting the chemical behavior of ions, particularly their reactivity and how they interact with other charged species.

Ions and Neutral Atoms

The difference between ions and neutral atoms lies in their electrical charge. A neutral atom has an equal number of protons and electrons, resulting in no net charge. An ion, on the other hand, has an unequal number of protons and electrons, leading to a positive or negative net charge. Ions are formed when atoms gain or lose electrons, typically during chemical reactions.

Ions are crucial components in many chemical processes, including the formation of salts and the conduction of electricity in electrolyte solutions. Understanding the concept of ions is pivotal when studying chemical reactions and the properties of substances. For example, in our step-by-step solution, the atom has 16 protons and 18 electrons, making it an ion with a -2 charge because of the two extra electrons. This ion can now engage in chemical reactions that neutral sulfur atoms cannot.