CLOSED October 20th. Sign up for our newsletter to learn more!
 

Atoms, Molecules & Matter

An atom is the smallest particle that comprises a chemical element. The concept of the atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods. During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the 'atom' was not indivisible. The principles of quantum mechanics were used to successfully model the atom.

In chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. This definition has evolved as knowledge of the structure of molecules has increased. Earlier definitions were less precise defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties. This definition often breaks down since many substances in ordinary experience, such as rocks, salts, and metals, are composed of atoms or ions, but are not made of molecules.

In science, matter is commonly defined as the substance of which physical objects are composed, not counting the contribution of various energy or force-fields, which are not usually considered to be matter per se (though they may contribute to the mass of objects). Matter constitutes much of the observable universe, although again, light is not ordinarily considered matter. Unfortunately, for scientific purposes, "matter" is somewhat loosely defined. It is normally defined as anything that has mass and takes up space. Matter can be in several different states, the most common being solids, liquids and gases.

Did you find this review helpful?
2 Items found Print
Discovering Atomos
from Classical Conversations
in Classical Conversations (Location: B03-04A)
We Were There at the Opening of the Atomic Era
We Were There #32
by James Munves
from Grosset & Dunlap
for 5th-9th grade
in We Were There Series (Location: A10-04G)