http://www.ck12.org Chapter 2. Matter
FIGURE 2.71
- He investigated pressure and other properties of gases, from which he inferred that gases must consist of tiny,
individual particles that are in constant, random motion. - He researched the properties of compounds, which are substances that consist of more than one element. He
showed that a given compound is always comprised of the same elements in the same whole-number ratio and
that different compounds consist of different elements or ratios. This can happen, Dalton reasoned, only if
elements are made of separate, discrete particles that cannot be subdivided.
Atomic Theory
From his research, Dalton developed a theory about atoms. Dalton’s atomic theory consists of three basic ideas:
- All substances are made of atoms. Atoms are the smallest particles of matter. They cannot be divided into
smaller particles, created, or destroyed. - All atoms of the same element are alike and have the same mass. Atoms of different elements are different
and have different masses. - Atoms join together to form compounds, and a given compound always consists of the same kinds of atoms
in the same proportions.
Dalton’s atomic theory was accepted by many scientists almost immediately. Most of it is still accepted today.
However, scientists now know that atoms are not the smallest particles of matter. Atoms consist of several types of
smaller particles, including protons, neutrons, and electrons. For the back story on Dalton’s ideas about atoms and
his place in the history of the atom, watch this video: http://www.youtube.com/watch?v=BhWgv0STLZs (9:03).
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5075For a musical version of the history of the atom, listen to “Atom Song” at this URL: http://www.youtube.com/watch
?v=0P3m_L-myog (3:29).