Uncombined elements, oxidation number

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 number of an element uncombined with other elements is 0. 

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. 

The oxidation numbers of Cl and Br in (a) have changed. Cl has changed from 0 to -1, while Br has changed from -1 to 0. (In diatomic molecules, the elements are considered to be in the uncombined state thus rule 1 applies.) There is no change in any oxidation number of any element in (b). Thus, (a)... 

The oxidation number, also known as the oxidation state, of an atom in a compound (or in a free element or polyatomic ion) is defined as the number of electrons possessed by a free (an uncombined) atom of the element— Nf ee—minus the number that is assigned to the atom in the compound (or element or ion)—... 

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... 

Every element has an oxidation number of zero when it is uncombined (rule 2, Section 16.1). This second simple rule allows us to predict about 100 more oxidation numbers. (Some compounds have atoms with oxidation numbers of zero. For example, the carbon atom in formaldehyde CH2O has an oxidation number of zero.)... 

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 an uncombined atom is zero. This is true for elements that exist as polyatomic molecules such as O2, CI2, H2, N2, Sg. 

In free elements (that is, in the uncombined state), each atom has an oxidation number of zero. Thus each atom in H2, Br2, Na, Be, K, O2, and P4 has the same oxidation number zero. 

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

Rule 1 The oxidation number of an element in its free (uncombined) state is zero (for example, Al(s) or Zn(s)). This is also true for elements found in nature as diatomic (two-atom) elements (H2,02, N2, F2, CI2, Br2, or I2) cuid for sulfur, found as Ss. 

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. 

All elements in their free state (uncombined with other elements) have an oxidation number of zero (e.g., Na, Cu, Mg, H2, O2, CI2, N2). 

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. 

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. 

Rapid and complete solvent evaporation is required for optimum performance. Atomisation occurs in the flame reaction zone, i.e. the conversion of sample molecules into atoms. Three factors affect the number of atoms formed. Firstly, the anion with which the metal atom is combined. Calcium chloride for instance is more easily dissociated than calcium phosphate. The second factor is flame temperature. Higher temperatures cause more rapid decomposition and, indeed, are often specifically required for elements which form refractory oxides. Finally, gas composition may affect the rate of atomisation if the constituents in the gas react with the sample or its derivatives. In the outer zone of the flame the atoms are burned to oxides. In this form they no longer absorb radiation at the wavelength of the uncombined ground state atoms. 

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