Subscript, in chemical formula

The chemical formula for water shows how formulas are constructed. The formula lists the symbols of all elements found in the compound, in this case H (hydrogen) and O (oxygen). A subscript number after an element s symbol denotes how many atoms of that element are present in the molecule. The subscript 2 in the formula for water indicates that each molecule contains two hydrogen atoms. No subscript is used when only one atom is present, as is the case for the oxygen atom in a water molecule. Atoms are indivisible, so molecules always contain whole numbers of atoms. Consequently, the subscripts in chemical formulas of molecular substances are always integers. We explore chemical formulas in greater detail in Chapter 3. 

At this point the formula can be written as C5H13 3O1.66, but you know that subscripts in chemical formulas are usually whole numbers. 

INTRODUCTION AND SECTION 3.1 The study of the quantitative relationships between chemical formulas and chemical equations is known as stoichiometry. One of the important concepts of stoichiometry is the law of conservation of mass, which states that the total mass of the products of a chemical reaction is the same as the total mass of the reactants. The same numbers of atoms of each type are present before and after a chemical reaction. A balanced chemical equation shows equal numbers of atoms of each element on each side of the equation. Equations are balanced by placing coefficients in front of the chemical formulas for the reactants and products of a reaction, nothy changing the subscripts in chemical formulas. 

H atoms (12 H2 molecules) for complete reaction. Only 9 H2 molecules are available, so H2 is the limiting reactant. Nine H2 molecules (18 H atoms) determine that 6 NH3 molecules are produced. One N2 molecule is in excess. 3.9 (a) Conservation of mass (b) Subscripts in chemical formulas should not be changed when balancing equations, because changing the subscript changes the identity of the compound law of constant composition), (c) H20(l), H20(g), NaCl(nq), NaCl(s)... 

Subscripts In chemical formulas, numbers wriften below the line (for example, in H O) to show numbers or ratios of atoms in a compound... 

The relative numbers of reactants and products in a reaction are given by the coefficients in the balanced chemical equation. These coefficients represent conversion factors similar to the subscripts in chemical formulas. For example, in the equation CH4 + 20j ... 

Note that the superscripted numbers in hybrid orbital notation are used to designate the number of atomic orbitals that have undergone hybridization. When the superscript is 1, it is not shown (analogous to the subscripts in chemical formulas). 

The drawings produced by students allow researchers to better conceptualize how some students interpreted a balanced chemical equations. This is especially useful in assessing their understanding of stoichiometric coefficients and the meaning of subscripts of chemical formulae. 

You are never allowed to change any subscripts in a formula. Changing subscripts changes the chemical nature of the substance, whereas changing a coefficient simply changes the amount of a substance. 

An unbalanced chemical equation is of limited use. Whenever you see an equation, you should ask yourself whether it is balanced. The principle that lies at the heart of the balancing process is that atoms are conserved in a chemical reaction. The same number of each type of atom must be found among the reactants and products. Also, remember that the identities of the reactants and products of a reaction are determined by experimental observation. For example, when liquid ethanol is burned in the presence of sufficient oxygen gas, the products will always be carbon dioxide and water. When the equation for this reaction is balanced, the identities of the reactants and products must not be changed. The formulas of the compounds must never be changed when balancing a chemical equation. That is, the subscripts in a formula cannot be changed, nor can atoms be added or subtracted from a formula. 

Chemical formulas reveal composition. The subscripts in the formula give the number of atoms of a given element in a molecule or formula unit of a compound or diatomic element. 

Recall that the chemical formula for a compound indicates the types of atoms and the number of each contained in one unit of the compound. For example, freon has the formula CCI2F2. The subscripts in the formula tell you that one molecule of CCI2F2 consists of one atom of carbon, two atoms of chlorine, and two atoms of fluorine that have chemically combined. The ratio of carbon to chlorine to fluorine is 1 2 2. 

Chemical formulae—use subscripts, superscripts, parentheses, and symbols appropriately in chemical formulae. 

Analyze When balancing a chemical equation, can you adjust the subscript in a formula Explain. 

When balancing a chemical equation, why is it not permissible to adjust the subscripts in the formulas of the reactants and products What would changing the subscripts within a formula do What do the coefficients in a balanced chemical equation represent Why is it acceptable to adjust a substance s coefficient but not permissible to adjust the subscripts within the substance s formula ... 

Many elements are found in nature in molecular form that is, two or more of the same type of atom are bound together. For example, the oxygen normally found in air consists of molecules that contain two oxygen atoms. We represent this molecular form of oxygen by the chemical formula O2 (read "oh two"). The subscript in the formula tells us that two oxygen atoms are present in each molecule. 

The composition of a compound is given by its chemical formula. A chemical formula indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts. The chemical formula of a molecular compound is referred to as a molecular formula. 

Empirical formulas are the simplest chemical formulas they are written by reducing the subscripts in molecular formulas to the smallest possible whole numbers (without altering the relative numbers of atoms). Molecular formulas are the true formulas of molecules. As we will see in Chapter 3, when chemists analyze an unknown compound, the first step is usually the determination of the compound s empirical formula. Sample Problem 2.6 (p. 54) lets you practice determining empirical formulas from molecular formulas. 

The number before each formula, such as the 5 before the O2, is known as its COEFFICIENT. The coefficient is a multiplier for the entire formula, never for only a part of it. Thus, 3CaCl2(H20)8 includes 3 Ca atoms, 6 Cl atoms, 36 H atoms, and 18 O atoms, It should be stressed that the subscripts in the formulas must not be altered. This error would alter the nature of the substances involved, thereby violating the experimental observation H2O2 is the formula for hydrogen peroxide, different from water, HjO. Also, the balanced equation is a statement of the relative numbers of moles of reactants and products involved in a chemical change. It does not, however, show the actual processes (Chapter 20) by which reactants are converted to products. 

The number of atoms of each element that make up a molecule or formula unit can be seen in the formulas. The numbers written as subscripts in the formulas, such as the 2 in the formula for water, H2O, and the 2 and the 4 in the formula for potassium chromate, K2Cr04, represent the number of atoms of the elements immediately to the left of each subscript in the formula. If there is no subscript immediately to the right of an element symbol, then there is only one atom of that element in the molecule or formula unit. Thus, in a molecule of water, H2O, there are 2 atoms of hydrogen and one atom of oxygen that are chemically combined. In a formula unit of salt, NaCl, there is one atom (ion) of each element, sodium and chlorine. In a formula unit of potassium chromate (also an ionic compound), K2Cr04, there are two atoms of potassium, one atom of chromium, and four atoms of oxygen. Thus chemical formulas are reasonable representations of the molecules and formula units of which compounds are composed. 

Changing the subscripts in the formulas is incorrect because this changes the identity of the chemical that is involved in the reaction. For example, the water formation reaction can be balanced by placing a 2 as a subscript to the O on the right. 

We have seen that the subscripts in a chemical formula indicate the number of atoms of each type of element in a compound. For example, one molecule of NH3 consists of 1 N atom and 3 H atoms. If we have 6.022 X 10 molecules (1 mol) of NH3, it would contain 6.022 X 10 atoms (1 mol) of N and 3 X 6.022 X 10 atoms (3 mol) of H. Thus, each subscript in a formula also refers to the moles of each kind of atom in 1 mol of a compound. For example, the subscripts in the NH3 formula specify that 1 mol of NH3 molecules contains 1 mol of N atoms and 3 mol of H atoms. 

The molar mass of a compound is the sum of the molar mass of each element in its chemical formula multiplied by its subscript in the formula. 

In this sequence, the subscripts ox , red determine the mode of preferable 4a-bond dissociation, which is ambiguous in the case of SR (64, 200) viz. a matter of the environment. The chromophore, however, remains the same which means that the change of redox-state implied in this sequence cannot easily be followed by spectrophotometry. In chemical formulae this appears trivially true, but not so for a biochemist dealing with structurally unknown and perhaps shortlived spectral flavin intermediates. Analogous problems arise with flavin complexed by a redox active metal such as Fe V where the redox shuttle can either occur between flavoquinone and -semiquinone, or between the latter and the flavohydroquinone. In such a case the use of dots as a formal marker for the radical state is questionable, since it might be mistaken for the spin state which may or may not be known. 

Molecular formula (Section 1.7) Chemical formula in which subscripts are used to indicate the number of atoms of each element present in one molecule. In organic compounds, carbon is cited first, hydrogen second, and the remaining elements in alphabetical order. 

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