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

ATOMS, MOLECULES, AND IONS
INTRODUCTION
The study of Chemistry centers on the concept of the atom and
molecules. In fact, knowledge of the atoms and molecules is helpful in
understanding the changes occurring in the environment and biological
systems allowing us to predict the behavior and the solution to any
problem observed in the behavior of these systems.
Question: How did our understanding of atoms evolved?

Basic Laws of Matter
John Dalton (1766-1844) is known as the father of modern
atomic theory because he was the first to explain the concept of
atoms with scientific basis. The theory explains several concepts
that are relevant in the observable world: the composition of a
pure gold necklace, what makes the pure gold necklace different
than a pure silver necklace, and what occurs when pure gold is
mixed with pure copper.
There are three basic laws of matter which served as the
foundations of the postulates of Dalton’s Atomic Theory: (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 an
important idea in ancient Greek philosophy
that argues that what exists now has always
existed, since no new matter can come into
existence where there was none before.
Antoine Lavoisier
(1743-1794) restated
this principle for chemistry with the law of conservation of mass , which
"means that the atoms of an object cannot be created or destroyed but
can be moved around and be changed into different particles. " This law
says that when a chemical 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 a
chemical reaction remains constant .
Law of Definite Proportions
The law of definite proportions was formulated by Joseph Proust (1754-1826). Otherwise
known as the Law of Constant Composition or Proust's Law, this law states that if a compound is
broken down into its constituent elements, the masses of the constituents will always have the
same 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 mass
regardless of its source or method of preparation .

The Law of Definite Proportions applies only to reactions in which elements are reacted
together to form the same product. For example, while
the Law of Definite Proportions can be used to compare