Download Chapter 4: Conceptual Science Teaching

A.
The atoms would be packed tightly together. They would look like a solid material without
any empty spaces between the atoms.
B.
I would see vibrating atoms arranged in an orderly way with spaces between them. There
would be nothing in the spaces, not even air.
C.
I think I would see atoms not moving and arranged in an orderly way. There would be
space between the atoms. The space would be filled with air.
D.
I think I would see atoms in the shape of small cubes. Each of these cubes would join
together to form a larger cube of salt.
E.
I think I would see lots of vibrating atoms connected together by little lines. The lines
connecting each atom give them a definite cube shape.
F.
I think I would see individual atoms moving from place to place. They would be moving all
about the inside of the crystal shape.
The best answer is B. salt is an example of a crystalline ionic lattice. A salt crystal is made up of a
structure of orderly repeating sodium and chlorine ions. This structure is caused by the electrostatic
attraction between negatively and positively charged ions and gives salt grains its cubic shape. The
ions are closely locked into position and can only vibrate. There is empty space between the atoms in
the crystal, but it is not filled with air. The material is pure salt, not a mixture of salt with air. The lines
that are sometimes used in drawings or models are not actual physical structures but they
representations of the attraction among the ions.
Example 13: Forces
Link with curriculum Physics:
Grade 8, chapter 2, lesson 1 (2010)
A person pulls a box across the floor. Which statement is correct?
A.
The box moves forward because the person pulls forward slightly harder on the box than the
box pulls backward on the person.
B.
Because action always equals reaction, the person cannot pull the box – the box pulls
backward just as hard as the person pulls forward, so there is no motion.
C.
The person gets the box to move by giving it a tug during which the force on the box is
momentarily greater than the force exerted by the box on the person.
D.
The personʼs force on the box is as strong as the force of the box on the person, but the
frictional force on the person is forward and large while the backward frictional force on the
box is small.
Answer D is correct. The force exerted by the person on the box is equal to that exerted by the box
on the person. The person moves forward because of a forward frictional force exerted by the floor.
The frictional force exerted by the floor on the box is much smaller.
Student Centred Approaches for Science Education – Part 2
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