Uncombined elements, oxidation

Uncombined elements are all given zero oxidation state. Consider (a) manganese in the permanganate ion, MnO there are four... 

All elements when uncombined have oxidation numbers equal to 0. (Some also have oxidation numbers equal to 0 in some of their compounds, by the way.)... 

The oxidation numbers of the atoms in uncombined elements are zero. 

The oxidation number of a neutral compound is zero. The oxidation number of an uncombined element is zero. 

If uncombined elements are among the reactants, an electron-transfer reaction is the only possibility. Metals can react only as reducing agents nonmetallic elements only as oxidizing agents. 

Humans have invented ways to extract iron from its compounds in order to take advantage of its properties. Does iron remain in its uncombined elemental form once it has been extracted No, it doesn t. Instead, it forms rust, or iron(lll) oxide, Fe203. How do we know that rust and iron are different substances One way to check is to test a physical property, such as magnetism. In this activity, you will use magnetism to compare the properties of iron and rust. 

The oxidation number of any uncombined element is zero. Because the element is not combined with any other element, there is either one atom alone or a group of identical atoms. Because the atoms are alike, the electrons are shared equally, and the number controlled is equal to the number in the free... 

Ans. Rule 2 Uncombined elements have zero charges, and so the oxidation numbers must add up to zero. Since all the atoms are the same, all the oxidation numbers must be the same—0. Rule 3 For monatomic ions, the oxidation numbers of all the atoms add up to the charge on the ion. Since there is only one atom (it is monatomic), the oxidation number of that atom must add up to the charge on the ion that is, it is equal to the charge on the ion. 

The oxidation number of the atoms in any free, uncombined element is zero. This includes polyatomic elements such as H2, O2, O3,... 

In an uncombined element, all of the atoms are uncharged (neutral). For example, sodium metal contains neutral sodium atoms, and chlorine gas is made up of CI2 molecules, each of which contains two neutral chlorine atoms. Therefore, an atom in a pure element has no charge and is assigned an oxidation state of zero. 

The oxidation state of an atom in an uncombined element is 0. The oxidation state of a monatomic ion is the same as its charge. 

As a starting point, the oxidation number of an uncombined element, regardless of whether it is monatomic or diatomic, is zero. Rules for assigning oxidation numbers are summarized below. 

Oxidation numbers, sometimes called oxidation states, are positive or negative numbers assigned to the elements in chemical formulas according to a set of rules. The following rules will be used be sure to note that Rule 1 applies only to uncombined elements—that is, elements in their free state. Rules 2 through 7 apply to elements combined to form compounds or ions. 

It is also useful to note the following. Except when they are combined with oxygen, many elements have only one oxidation number (in addition to zero for the uncombined element), for example, + 1 for the alkali metals (Na, K, Li, Rb, and Cs), +2 for the alkaline earth metals (Ca, Sr, Ba, and Mg), and -1 for the halogens (F, Cl, Br, I, and At). Other elements can have several oxidation numbers. 

Reactants and products in redox reactions are not limited to monatomic ions and uncombined elements. Elements in molecular compounds or polyatomic ions can also be oxidized and reduced if they have more than one nonzero oxidation state. An example of this is provided in the reaction between the copper penny and nitric acid in which the nitrate ion, NO, is converted to nitrogen dioxide, NO2. Nitrogen is reduced in this reaction. Usually, we refer to the oxidation or reduction of the entire molecule or ion. Instead of saying that the nitrogen atom is reduced, we say the nitrate ion is reduced to nitrogen dioxide. 

Let us make a few observations about these rules before we look at some examples of their use. First, in Rule 1 the uncombined element is an element that is in the free elemental state, or the state of the element when it is not combined with any other element. For most elements, this is shown by the use of the symbol of the element, as found in the periodic table. For example, the oxidation numbers of silver metal (Ag), radon gas (Rn), and mercury liquid (Hg) would be 0. However, there are some elements whose free elemental state refers to diatomic molecules, or molecules that consist of two atoms of the element that are covalently combined. This list includes hydrogen gas (H2), fluorine gas (F2), nitrogen gas (Nj), oxygen gas (O2), chlorine gas (CI2), bromine liquid (Br2), and iodine solid (I2). Thus, whenever these diatomic symbols are observed, these substances are in their free elemental state and the correct oxidation number to be assigned would be 0. 

The oxidation number of any uncombined element is zero. For example, the oxidation number of each atom in Sg, Clj and Zn is zero. 

What is the oxidation state of the atoms in an uncombined element Does it depend on whether the element occurs as a diatomic molecule (Oj, N2) or as a larger molecule (P4, Ss) ... 

Most of the reactions of the halogens are of the oxidation-reduction type. The halogens are so reactive that they do not occur uncombined in nature and they must be made from halide compounds (salts). We shall consider briefly the preparation of the elements and then explore some of the very interesting chemistry of this family. 

Magnesium (eighth most abundant element) is found principally as Mg+2 ion in salt deposits, particularly as the slightly soluble carbonate, MgC03, and also in sea water. The element is oxidized by atmospheric oxygen and is not found in an uncombined state in nature. 

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