Secondary Science - Particles
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CHAPTER 11-PARTICLES
Making Sense of Secondary Science: Research into Children’s Ideas
Rosalind Driver, Anne Squires, Peter Rushworth, Valerie Wood-Robinson
Summarized by Patricia Gonzalez
DEVELOPMENT OF PARTILE IDEAS ABOUT MATERIALS
From Piaget's interviews with children, it was understood that children have the idea that materials are made of small bits called atoms. Further research has shown that the attributes children give these atoms are scientifically incorrect. For example, children think atoms have similar properties to the parent material. Children will often attribute the macro-properties like color, hardness, coldness, etc. of a material to its constituant atoms, rather than the groups of atoms. It appears that children do not understand it is the interaction of the atoms that give rise to the properties.
Particle ideas about solids
The solid state of matter seems to be the area of many misconceptions. Students depict solids as ordered arrangements of atoms, but could not explain how they were held together. The idea of the bonds between atoms in a solid was not understood. Neither could the children explain incompressibility or the vibration of molecules in a solid. The researchers concluded that students understood individual atoms of a solid, but when it came to behavior of groups of atoms in a solid, and their interactions, students did not understand. As the students grew older more understood the bonded nature of atoms in a solid.
Particle ideas about liquids
The liquid state of matter was the area of most misconceptions. Most students regard the liquid state as a halfway state between solids and gases. Students often over-estimated the spacing and speed of the particles in a liquid. The students did not understand that liquids are in constant motion rolling over one another. They depicted spacing much furtehr than it should have been showing that molecules in a liquid move apart from each other instead of rolling over one another. Subsequently, the students depicted liquids with no fixed volume. The students' depiction would have allowed for compressibility of a liquid and would not explain the process of evaporation.
Particle ideas about gases
Overall, students were able to depict atoms in the gaseous state with the most accuracy towards the accepted model. The trouble of depictions of solids and liquids may have steemed from a lack of understanding of the forces holding the molecules and atoms together, the bonds. Students had trouble understanding intrinsic intermolecular forces and bonds.
PARTICLE IDEAS ABOUT CHANGE OF STATE
Particle ideas about MELTING
Most students thought that heat makes the particles in a solid piece of ice move further apart causing it to melt. The students used the generalized model that the volume of a substance increases as its temperature rises. This is incorrect with water and ice since the density of ice is less than that of liquid water due to the lattice structure of ice. The angle of hydrogen to oxygen allows for gaps causing ice to be less dense. When ice melts the lattice structure of ice gives way to molecules that roll ove one another.
Particle ideas about FREEZING
Students' ideas about freezing included particles becoming more compact. This can often lead students to the idea that solid ice will not take up as much room as liquid ice. Again, this generalization that solids compress and liquid particles move away from each other does not hold true for water. The students did not understand hydrogen bonding in ice that allows for gaps bewteen the molecules and the solid state of water/ice to take up more room than that of liquid having the same amount or mass.
Particle ideas about EVAPORATION AND CONDENSATION
Very few of the students in this study understood that the molecules undergoing evaporation get the energy from the surroundings. When enough energy is gained the hydrogen bonds are broken and the molecule becomes a gaseous state. Only one student understood when water condenses, the molecules lose enough energy to link back up with other water molecules and become a liquid. Overall, it appears that students misunderstandings stem from not grasping intermolecular forces and bonds between atoms and molecules giving rise to the observable properties.
Particle ideas about SOLUTION
When students were asked to depict a solution of sugar in water, most gave an illustration without showing the water. They depicted a continuous shade of liquid sugar. It seems that these students are not understanding the interaction of sugar molecules with the water molecules. Again, intermolecular forces are at the root of the misunderstanding.
ATTRIBUTES OF PARTICLES
Conceptions of atomic size and mass
Once students understood somewhat of the minuteness of the size of atoms and molecules, most misunderstood that they have zero or negligible mass. Students seemed to have trouble with the concept of single atom/molecule interactions and with the idea that millions and millions of particles are needed to observe any change. The mole concept seemed to be not even mentioned, yet appropriate here.
Conceptions of internal structure of molecules
When asked to depict N2O4, students incorrectly depicted it as fragments of N2 and 04. When the molecule was drawn as a gas, the students depicted the bonds between the atoms in the molecule having a greater bond length. They thought the atoms in the molecule are further apart, not that the molecules are further apart or separate from other molecules.
PARTICLE MODELS OF ELEMENTS AND COMPOUNDS
Students are to leave school with an understanding of forces/chemical bonds holding units within a molecule together. It appears though that students have come up with a variety of intermediate visuals of the structure of materials. Students often have trouble distinguishing between chemical substances and molecular particles that comprise them. Students have trouble depicting the chemical combination of elements on the particle level. Student depictions of an example formation of a ionic solid included: randomly mixing the particles, one particle surrounding the other, incorrectly joining the particles in ratios, and finally joining the particles alternately having a same structure throughout the assemblance.
PARTICLE MODELS OF GIANT IONIC LATTICES
Upon depicting the formation of sodium chloride, students were capable of describing the transfer of electrons to form the ionic bond, but most confusion arose around the lattice structure with the misinterpretation that one bond was ionic and the remaining five were physical bonds. The students appear to not understand the models representation of the crystal lattice of sodium chloride.
