QUESTION: Assume circles and squares in the figures below represent atoms. According Dalton’s atomic theory, which of the figures below best represents a sample of a compound? A B C D SCRIPT: Assume circles and squares in the figures below represent atoms. According Dalton’s atomic theory, which of the figures below best represents a compound? PAUSE Figure A and D represent samples that have only one kind of atom. Figure A only has red circles, while figure D only has blue squares. Therefore figures A and D represent a sample of an element. Figure A represents an element that exists as a monatomic gas CALLOUT “Monatomic element” While Figure D represents an element that exists as a diatomic gas because the atoms are paired up. CALLOUT “Diatomic element” Figures B and C both represent samples with two elements. But if you were to randomly draw out samples from Figure C, you will always get a 1-to-1 ratio of Red circles to blue squares. That would not be the case for Figure B. Therefore Figure C represents a COMPOUND. Its contents have a definite composition The correct answer is Figure C. CALLOUT “Definite Composition” Figure B is an example of a mixture of two elements. 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. 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: 1-13-2 © 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