Question

Determine the charge of each of the following: a. a silver atom that has lost one electron b. a bromine atom that has gained one electron c. a chromium atom that has lost three electrons

Short answer

The charge of a silver atom (Ag) after losing one electron is +1, a bromine atom (Br) after gaining one electron is -1, and a chromium atom (Cr) after losing three electrons is +3.

Step-by-step solution

Determine the charge of a silver atom that has lost one electron

A silver atom (Ag) has an atomic number of 47, which means it has 47 protons and, when neutral, it has 47 electrons. When a silver atom loses one electron, it will have one more proton than electrons, giving it a positive charge. The charge is determined by the difference in the number of protons and electrons. Since it has lost one electron, its charge will be +1.

Determine the charge of a bromine atom that has gained one electron

A bromine atom (Br) has an atomic number of 35, indicating it has 35 protons. In its neutral state, it also has 35 electrons. When a bromine atom gains one electron, it now has more electrons than protons. This extra electron gives the bromine a negative charge. Therefore, the charge of a bromine atom that has gained one electron will be -1.

Determine the charge of a chromium atom that has lost three electrons

A chromium atom (Cr) has an atomic number of 24, meaning it has 24 protons. When it is neutral, it has 24 electrons. If a chromium atom loses three electrons, it will have three more protons than electrons. As a result, the chromium atom will have a charge of +3, since it has a deficit of three electrons.

Key concepts

Ion Charge

Understanding the concept of ion charge is fundamental in chemistry. An ion is an atom or molecule with a net electric charge due to the loss or gain of one or more electrons. When an atom loses electrons, it becomes a cation, which carries a positive charge. Conversely, when an atom gains electrons, it becomes an anion, with a negative charge. The magnitude of the charge is directly related to the number of electrons lost or gained.

Take for example a silver atom. In its neutral state, a silver atom has an equal number of protons and electrons. If it loses one electron, like in exercise part (a), there will be one more proton than electrons, resulting in a positive charge, specifically a +1 charge. It's important for students not to confuse the loss of a negatively charged electron with becoming negatively charged; the opposite is true. Losing a negative charge makes the atom's charge more positive.

Oxidation States

The oxidation state, often called oxidation number, is a concept that provides insight into the electronic structure of an atom within a compound or molecule and shows the degree of oxidation (loss of electrons) or reduction (gain of electrons) an atom has undergone. Each atom in a molecule can be assigned an oxidation state, which can be positive, negative, or zero.

For instance, in part (c) of the exercise, a chromium atom loses three electrons. This changes its oxidation state from 0 (in the elemental state) to +3. Understanding oxidation states is crucial when studying redox reactions, as they help chemists keep track of electron transfer. The rules for assigning oxidation states can be detailed, but knowing that a neutral atom has an oxidation state of 0 is a good starting point for novices.

Electron Transfer

The process of electron transfer is at the heart of many chemical reactions, particularly redox (reduction-oxidation) reactions. Electron transfer involves the movement of electrons from one atom to another, altering the ion charges and oxidation states of the atoms involved. For example, in a basic electron transfer scenario such as part (b) of the exercise, a bromine atom gains an electron, which means it undergoes reduction. The bromine atom's charge changes from 0 to -1, indicating it now has an excess of one electron.

It's important to recognize that electron transfer has profound implications not just in inorganic chemistry but also in biological processes, where it plays a critical role in the generation of energy within cells. Understanding electron transfer is not only about tracking charges but also understanding how and why chemical bonds are made or broken during reactions.