General Chemistry
Oxidation numbers describe how many electrons an atom loses or gains when it breaks or forms a bond. These oxidation numbers essentially represent the charge an atom in a molecule would have if it were an ion. Using the mnemonic OIL RIG, it's important to remember that oxidation refers to the loss of electrons, while reduction refers to the gain of electrons. Free elements, which are not bonded to any other elements, have an oxidation number of zero. In molecules, the sum of the components' oxidation numbers is equal to the molecule's overall charge.
Elements in the periodic table generally follow a pattern that can be used to estimate oxidation numbers. Elements in Group 1 typically have an oxidation number of +1, and those in Group 2 have an oxidation number of +2. To the left of the noble gases, groups 17, 16, and 15 typically have oxidation numbers of -1, -2, and -3, respectively. Hydrogen, oxygen, and fluorine have specific oxidation numbers, with hydrogen typically at +1, oxygen at -2, and fluorine always at -1.
Lesson Outline
<ul> <li>Oxidation numbers</li> <ul> <li>An oxidation number describes how many electrons an atom loses or gains when it breaks or forms a bond</li> <li>Represents the charge an atom in a molecule would have if it were an ion</li> </ul> <li>Using the mnemonic OIL RIG</li> <ul> <li>Oxidation refers to the loss of electrons (Oxidation Is Loss)</li> <li>Reduction refers to the gain of electrons (Reduction Is Gain)</li> </ul> <li>Free elements</li> <ul> <li>Not bonded to any other elements</li> <li>Have an oxidation number of zero</li> </ul> <li>In molecules, the sum of the components' oxidation numbers is equal to the molecule's overall charge</li> <li>Elements in the periodic table and their typical oxidation numbers</li> <ul> <li>Group 1: +1</li> <li>Group 2: +2</li> <li>Group 17: -1</li> <li>Group 16: -2</li> <li>Group 15: -3</li> <li>Hydrogen: +1</li> <li>Oxygen: -2</li> <li>Fluorine: -1</li> </ul> </ul>
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FAQs
To assign oxidation numbers to elements of the ionic compounds, you should follow these steps: (1) Identify the charge of each ion; (2) assign the charge to the oxidation number of the corresponding element; (3) ionic compounds' overall charge should be zero, so add the oxidation numbers of the two elements, and they should equal zero. For example, in the case of sodium chloride (NaCl), sodium (Na) is a group 1 element, so its oxidation number is +1. Chlorine (Cl) is in group 17 and has an oxidation number of -1. The sum of the oxidation numbers is 0, which indicates a neutral compound.
OIL RIG is a mnemonic that helps one remember the concept of oxidation and reduction in terms of electron transfer. OIL stands for Oxidation Is Loss (of electrons), and RIG stands for Reduction Is Gain (of electrons). When a molecule loses electrons, its oxidation number increases, signifying oxidation. Conversely, when a molecule gains electrons, its oxidation number decreases, indicating reduction.
Electronegativity is a measure of an atom's ability to attract bonded electrons. It plays a significant role in determining oxidation numbers in chemical compounds. Elements with higher electronegativities tend to have more negative oxidation numbers when involved in chemical compounds, as they have a stronger attraction for electrons. This concept helps predict the possible oxidation states and ionic characters of chemical substances or compounds. For example, fluorine, which has the highest electronegativity, will essentially always have an oxidation number of -1 in its compounds.
Noble gases have fully-filled valence electron shells, which makes them chemically inert and stable. They rarely participate in chemical reactions as they have little tendency to lose, gain, or share electrons. Therefore, the oxidation numbers of noble gases in their elemental form are assigned as zero because there is no charge associated with their unreactive nature. However, under specific conditions or in certain compounds, noble gases can form chemical bonds and may exhibit oxidation numbers, such as xenon hexafluoroplatinate (XePtF6) where xenon has an oxidation number of +6.
