Atoms, Molecules and Ions (Chemistry).pdf - ATOMS,...

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ATOMS, MOLECULES, AND IONSINTRODUCTIONThe study of Chemistry centers on the concept of the atom andmolecules. In fact, knowledge of the atoms and molecules is helpful inunderstanding the changes occurring in the environment and biologicalsystems allowing us to predict the behavior and the solution to anyproblem observed in the behavior of these systems.Question: How did our understanding of atoms evolved?
Basic Laws of MatterJohn Dalton (1766-1844) is known as the father of modernatomic theory because he was the first to explain the concept ofatoms with scientific basis. The theory explains several conceptsthat are relevant in the observable world: the composition of apure gold necklace, what makes the pure gold necklace differentthan a pure silver necklace, and what occurs when pure gold ismixed with pure copper.There are three basic laws of matter which served as thefoundations of the postulates of Dalton’s AtomicTheory: (1) Law of Conservation of Mass(2) Law of Definite Proportions, and (3) Law of Multiple Proportions.Law of Conservation of Mass"Nothing comes from nothing" is animportant idea in ancient Greek philosophythat argues that what exists now has alwaysexisted, since no new matter can come intoexistence where there was none before.AntoineLavoisier(1743-1794)restatedthis principle for chemistry with thelaw of conservation of mass, which"means that theatoms of an object cannot be created or destroyed butcan be moved around and be changed into different particles." This lawsays that when achemical reaction rearranges atoms into a new product,the total mass of the reactants (substances before the chemical reaction)is the same as the total mass of the products (new substance(s) made).This law can be simply stated as,the total mass before and after achemical reaction remains constant.Law of Definite ProportionsThelaw of definite proportionswas formulated byJoseph Proust(1754-1826). Otherwiseknown as the Law of Constant Composition or Proust's Law, this law statesthat if a compound isbroken down into its constituent elements, the masses of the constituents will always have thesame proportions, regardless of the quantity or source of the original substance. In other words,a pure compound always contains the same elements combined in the same proportions by massregardless of its source or method of preparation.
The Law of Definite Proportions applies only to reactions in which elements are reactedtogether to form the same product. For example, whilethe Law of Definite Proportions can be used to compare

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