The atomic and kinetic theories of
matter
The Atomic Theory - chemical properties
The Modern Atomic Theory is used to describe the chemical behavior of
a substance or how elements and compounds react to form new substances.
The theory states that matter is made up of extremely small and numerous
particles called atoms. This theory has evolved over the past two millennia
from early Greek theories of matter, through the dawn of the modern scientific
era, in the early 1800s, to our present mathematical descriptions of matter.
Today,
scientists believe that the many and varied properties of matter can be
explained by the presence of atoms and the combinations of atoms to
form molecules and ionic crystals. Only in the past few years have modern
electron microscopes been able to detect individual atoms. The atomic
theory is one of the most tested and accepted theories in science and
is able to predict the behavior of matter to a high degree.
The term "atom" was derived from the original Greek hypothesis
put forward by Democritus, that all matter was made up of tiny unseen
particles he called "atomos", the indivisible.
The Kinetic Theory - physical properties
This theory of matter describes how atoms and molecules interact to form
the four physical states of matter: solids, liquids, gases and plasma.
The Kinetic Theory explains the properties of the physical phases and
the processes involved in changes of state, like melting and boiling,
in terms of the movement of particles and the forces of attraction between
particles. The Kinetic Theory can be used independently of the Atomic
Theory because it does not stipulate the type of particle in terms of
atoms or molecules.
The Kinetic or Particle Theory has five postulates describing the
physical behavior of matter. The postulates are:
- Matter is made of tiny unseen particles.
- There is space between the particles. In solids and liquids, this
space is quite small. In gases there is far more empty space than particles.
- There are attractive and repulsive forces between the particles. These
forces become weaker with distance between the particles and vary from
one type of particle to another.
- The particles are in constant motion in the form of vibrations, rotation
and translation movement.
- The particles move faster as the temperature increases.
Combining the two theories
The combination of Atomic Theory, to explain chemical
behavior of matter, and the Kinetic theory, to explain the physical properties
and transformations of matter, gives scientists two very powerful tools
with which to describe matter. See Atomic
theory - early models, Atomic
theory - modern models and Changes
in state for more on these theories.
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