4.6: Physcial and Chemical Changes- the Nanoscopic Level
- Page ID
- 366295
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- Classify changes in matter as physical or chemical on the particle level.
Physical Changes
Chemical and physical changes can also be understood using nanoscopic level illustrations. Representations of three physical changes are shown below. In all of these illustrations, the arrow represents the process of transformation. What is to the left of the arrow can be thought of as a "before" snapshot and what is to the right of the arrow can be thought of as an "after" snapshot.
The first illustration represents a phase change. The left square represents a solid and the right square represents a gas. Since the same particle--consisting of two hexagons--makes up both the solid and the gas, this is a physical change. The second illustration represents a solid being broken into smaller pieces. The particle in both the left square and the right square consists of a single circle. Finally, the third illustration represents a solid dissolving in a liquid. Neither particle represented--the one formed from a single circle or the one formed from two squares--changes during the process of dissolving.
What all of these changes have in common is that the particles themselves remain unaltered though the transformation. Whatever particles you start with in the left square, you end with in the right square. Another way of saying this is that no new pure substances are formed.
Chemical Changes
Nanoscopic level representations of three chemical changes are shown below.
What all these illustrations have in common is that new particles are formed while moving from the left square to the right square. In the first transformation a particle with a circle and a triangle is formed that did not originally exist. In the second illustration, a particle is formed that contains two triangles and another particle is formed that contains a single square. Originally, the only particle present contained a square and a triangle. Finally, a particle containing two hexagons is formed from a sample that originally contained particles with three hexagons.
The first illustration shows that a chemical change can sometimes include a change in state: here a solid disappears as it reacts and becomes part of the gas phase. The final illustration shows that it is possible for one sample of an element to change to another sample of an element. Even though the atoms themselves do not change, the way they bond together to form a particle is altered.