Definite ratio of atoms

Dalton argued that these laws are entirely reasonable if the elements are composed of atoms. For example, the reason that mass is neither gained nor lost in a chemical reaction is that the atoms merely change partners with each other they do not appear or disappear. The constant composition of compounds stems from the fact that the compounds consist of a definite ratio of atoms, each with a definite mass. The law of multiple proportions is due to the fact that different numbers of atoms of... 

Composition A pure substance the simplest building blocks of compounds. A pure substance composed of two or more elements chemically combined in a definite ratio of atoms. Composed of two or more pure substances physically mixed in no particular ratio of substances. 

Because the metal structure is locked by these atoms, the resulting compound is often much harder than the original metal, and some of the compounds are therefore of industrial importance (see under iron). Since there is a definite ratio of holes to atoms, filling of all the holes yields compounds with definite small atom-metal atom ratios in practice, all the holes are not always filled, and compounds of less definite composition non-stoichiometric compounds) are formed. 

An ordered distribution of spheres of different sizes always allows a better filling of space the atoms are closer together, and the attractive bonding forces become more effective. As for the structures of other types of compound, we observe the validity of the principle of the most efficient filling of space. A definite order of atoms requires a definite chemical composition. Therefore, metal atoms having different radii preferentially will combine in the solid state with a definite stoichiometric ratio they will form an inter-metallic compound. 

A compound is an electrically neutral substance that consists of two or more different elements with their atoms present in a definite ratio. Water, for instance, is a compound of hydrogen and oxygen, with two hydrogen atoms for each oxygen atom. Whatever the source of the water, it has exactly the same composition indeed, a substance with a different ratio of atoms would not be water Chemists took a big step forward when they first noticed this invariance of composition, for it suggested an underlying order in nature. They summarized the observation as the law of constant composition. The law was important historically, because it suggested to chemists that compounds consisted of specific combinations of atoms. 

Unusual are measurements for which a direct link to the mole is useful. We should probably not talk about traceability in that connection, because that term is defined as a relation between measured values. An acceptable chain of measurements for compound X of established purity, containing element E that has isotope E and that would establish a link to the mole, then would take one of the following general routes the amount of substance (X)->n(E)->n( E)-> (12C) or n(X)->n(E)-> (C)-> (12C). The ratio of atomic masses m( E)lm( 12C) is also involved in the definition, but that ratio is known with a negligible uncertainty compared with the other links in the chain. Clearly, only in a few instances will laboratories attempt to execute such a chain of measurements for a link to the SI unit. Is it fear that such a difficult process is involved in every chemical analysis that has kept so many chemists from using the mole as the way to express chemical measurement values Or is it just habit and the convenience of a balance that subconsciously links amount of substance to amount of mass ... 

The ratio of atoms in the simplest formula must be a whole-number ratio (by definition). To convert the ratio 1 1 1.5 to a whole-number ratio, each number in the ratio was multiplied by 2, which gave the simplest formula Na2S20j. 

Today, it is common to think of these laws in terms of atoms of the elements as opposed to grams of the elements. Instead of a ratio of masses, we talk in terms of a ratio of atoms, and the definition of compound becomes easier to understand. Compounds are pure substances composed of two or more elements in a definite, nonchanging ratio of atoms. 

Compounds result from the chemical combination of a specific ratio of atoms of different elements. (Follows directly from the fact of definite composition.)... 

In the period 1775-1780, Lavoisier established chemistry as a quantitative science by proving that in the course of a chemical reaction the total mass is unaltered. The conservation of mass in chemical reactions proved ultimately to be a death blow to the phlogiston theory. Shortly after Lavoisier, Proust and Dalton proposed the laws of definite and multiple proportions. In 1803 Dalton proposed his atomic theory. Matter was made up of very small particles called atoms. Ever kind of atom has a definite weight. The atoms of different elements have different weights. Compounds are formed by atoms which combine in definite ratios of (usually small) whole numbers. This theory could give a satisfying interpretation of the quantitative data available at the time. 

The CD -ferrocene complexes were characterized by elemental analysis, IR, UV, and H-NMR spectra. Stoichiometries were determined by elemental analysis, and especially the iron content measured by atomic absorption analysis and from the H-NMR spectra, which show all the complexes obtained here are stoichiometric compounds and have definite ratios of CD/guest depending on the combinations of host and guest. Table I shows the results of the preparation of inclusion compounds of CDs with ferrocene. 3 CD formed 1 1 inclusion compounds with ferrocene. 

The precise ratio of atoms of different elements in a compound is responsible for the Law of Definite Composition, also called the Law of Constant Composition. This law states that any compound is always made up of elements in the same proportion by mass (weight). The source of the compound does not matter. For example, 100 grams of pure water always contains 11.1 grams of hydrogen and 88.9 grams of oxygen. It makes no difference if the water comes from a pond in Kansas, a river in South America, a lake in the Alps, or a comet in the far reaches of the solar... 

The compositions and chemical formulae for metal oxides and other inorganic compounds are usually written with a definite ratio of cations to anions, e.g. MaOb where a and b are usually small integers determined by the valence of the constituent atoms. In crystalline compounds this also reflects that the structure contains different types of sites (e.g. close-packed sites and tetrahedral or octahedral interstices) in simple ratios and that these are selectively and systematically filled with cations or anions. When the oxide MaOb contains M and O atoms in the exact ratio a b, it is said to have a stoichiometric composition. 

The regular atoms on their normal sites and the point defects occupy particular sites in the crystal structure and these have been termed structural elements by Kroger, Stieltjes, and Vink (1959) (see also Kroger (1964)). As discussed in Chapter 2, the rules for writing defect reactions require that a definite ratio of sites is maintained due to the restraint of the crystal structure of the compounds. Thus if a normal site of one of the constituents in a binary compound MO is created or annihilated, a normal site of the other constituent must simultaneously be created or annihilated. 

Again, this ratio is the same for every sample of ammonia. The law of definite proportions also hints at the idea that matter is composed of atoms. Compounds have definite proportions of their constituent elements because the atoms that compose them, each with its own specific mass, occur in a definite ratio. Since the ratio of atoms is the same for all samples of a particular compound, the ratio of masses is also the same. 

An alloy is a metallic material that contains more than one element. Some alloys are simply solid solutions, while others are specific compounds with definite ratios of the component elements. Alloys have metallic properties, but they can consist of either two or more metals or a metal and a nonmetal. We broadly classify alloys as substitutional or interstitial, hi a substitutional alloy, one metal atom substitutes for another in the crystal stracture. The crystal structure may either stay the same upon the substitution, or it may change to accommodate the differences between the atoms. In an interstitial alloy, small, usually nonmetallic atoms fit in between the metallic atoms of a crystal. The alloy maintains its metallic properties with these interstitial atoms in the structure. 

Substances react according to definite ratios of numbers of particles (atoms, ions, formula units, or molecules). The following balanced chemical equation shows that two atoms of aluminum react with three molecules of iodine to form two formula units of aluminum iodide. 

In 1903, Rutherford and associates were finally able to deflect the a-rays by electric and magnetic fields, showing that these are positively charged. Measurement of the charge-to-mass ratio indicated that a-rays were of atomic dimensions. In 1908 definitive experiments showed a-rays to be doubly chaiged helium atoms, ie, helium nuclei. 

The equivalent weight of an ion (or an element) is the ratio of its formula weight to its valence. According to an alternative definition that is also suitable for compounds, an equivalent weight represents the amount of a substance which will react with one atomic weight of hydrogen or its chemical equivalent. 

Since an atom of a given element gives rise to a definite, characteristic line spectrum, it follows that there are different excitation states associated with different elements. The consequent emission spectra involve not only transitions from excited states to the ground state, e.g. E3 to E0, E2 to E0 (indicated by the full lines in Fig. 21.2), but also transisions such as E3 to E2, E3 to 1( etc. (indicated by the broken lines). Thus it follows that the emission spectrum of a given element may be quite complex. In theory it is also possible for absorption of radiation by already excited states to occur, e.g. E, to 2, E2 to E3, etc., but in practice the ratio of excited to ground state atoms is extremely small,... 

Attempts to determine how the activity of the catalyst (or the selectivity which is, in a rough approximation, the ratio of reaction rates) depends upon the metal particle size have been undertaken for many decades. In 1962, one of the most important figures in catalysis research, M. Boudart, proposed a definition for structure sensitivity [4,5]. A heterogeneously catalyzed reaction is considered to be structure sensitive if its rate, referred to the number of active sites and, thus, expressed as turnover-frequency (TOF), depends on the particle size of the active component or a specific crystallographic orientation of the exposed catalyst surface. Boudart later expanded this model proposing that structure sensitivity is related to the number of (metal surface) atoms to which a crucial reaction intermediate is bound [6]. 

Ans. The compounds have different ratios of hydrogen to oxygen atoms, and thus different mass ratios. The law of definite proportions applies to each compound individually, not to the two different compounds. H20 and H202 each follow the law of definite proportions (and together they also follow the law of multiple proportions). 

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