QUESTION: Assume that circles and squares in the figure below represent atoms. According to Dalton’s theory, which of the changes indicated is possible? A C 2 RB  B2 + 2 R B SCRIPT: Assume that circles and squares in the figure below represent atoms. According to Dalton’s theory, which of the changes indicated is possible? PAUSE Arrows are generally used in Chemistry to indicate a change. For example, choice A, the change being suggested is that one of the red circles disappeared. There are four red circles before the change HIGHLIGHT four red circles in the top box as you count One…two…three… four But there are only three after the change HIGHLIGHT three red circles in bottom box as you count One… two… three Choice A, then, represents a change where an atom is destroyed. This is contrary to Dalton’s assumption that atoms are indestructible. Therefore, according to Dalton, this is impossible. In choice B, the figure suggests that a blue square is created. There are only two blue squares before the change. HIGHLIGHT as you count One… Two.. And three after the change. One… Two… Three This is contrary to Dalton’s assumption atoms are neither created nor destroyed. Therefore, the correct answer must be choice C. Let’s examine it. In choice C, we have exactly the same number of atoms of each kind before and after… Four red circles and two blue squares. This illustrates how Dalton explains a chemical change. CALLOUT “Chemical change” According to Dalton, when we see chemical changes, atoms are neither created nor destroyed. They simply rearrange. That is… they change the way they associate with other atoms. If we represent red atoms by R and blue atoms by B, the change that occurs here is CLICK Two RB yields B2 plus 2 R Before the change, we have two pairs of red circle and blue square. HIGHLIGHT “2 RB” The atoms in these two pairs rearrange to give us a pair of blue squares, and two red circles. HIGHLIGHT “B2” and “2 R” CLICK A final note: Dalton did NOT assume imagine atoms as having different shapes or colors. Dalton’s atoms are all spherical and they only differ in mass. Color and shape are shown here to facilitate distinction between atoms of different elements. CLICK PAUSE END RECORDING NOTE: Dalton’s atoms differ only in mass, not shape or color. Color and shape are used here to facilitate distinction.

Video ID: 1-13-3 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08