MI BIG
Changes in Matter IV.2
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(Inspiration)
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All students will investigate, describe and analyze ways in which
matter changes.
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All students will explain how visible changes in matter are related to
atoms and molecules.
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All students will explain how changes in matter are related to changes
in energy and how living things and human technology change matter and
transform energy.
Overview
The world is filled with a variety of solids, liquids and gases. Examples
are everywhere. When ice cube trays are filled with water and they are set
in the freezer a change of state is expected. Predictably, the liquid
water will become a solid, ice.
Essential Background Narratives
Investigate, describe and analyze ways in which matter changes.
Explain how visible changes in matter are related to atoms and molecules.
Explain how changes in matter are related to changes in energy and how
living things and human technology change matter and transform energy.
Matter can be changed in many ways. Changes of state and changes in size
and shape are two common changes that are important in the elementary
school. All matter can exist as a solid, liquid, or gas depending on the
temperature and pressure. In the early elementary years, instruction
focuses on melting and freezing. In the later elementary years, changes
such as dissolving and evaporating are added to students' experiences.
Changes in the size of familiar objects such as making snowballs or
crumbling cookies can be a part of the elementary grade experiences.
Students might also prepare mixtures and separate them to show how matter
can be changed. Using filtration and sieves students can investigate many
different types of mixtures. In the later elementary years, dissolving
soluble substances and evaporation should also be included.
In the middle school years, sublimation, thermal expansion and contraction
are concepts that are added to evaporation and condensation. Experiences
that help students understand that mass is conserved as matter is changed
are also important at this level. Chemical changes are important in the
middle school years. Students should describe common chemical changes in
terms of properties of reactants and products by the middle school years.
Burning, rusting and photosynthesis are but some of the common chemical
changes students should investigate.
Matter is never created or destroyed in ordinary physical and chemical
changes. All matter is made up of atoms, which are far too small to be
seen directly though a microscope. There is nothing occupying the spaces
between the molecules. The space between the particles of a gas, liquid,
or solid is empty but the difference in spacing between solids and liquids
is not as large as students tend to represent it. Atoms of molecules are
perpetually in motion.
The motion and arrangement of molecules as they interact with energy
determine the state of matter. Solids have a definite shape and volume. In
solids, the atoms are closely locked in position in a regular pattern and
can only vibrate. Liquids flow and take the shape of the container. In
liquids, the atoms or molecules have higher energy, are more loosely
connected, and can slide past one another, moving in a random motion.
Gases expand or contract to fill the space available to them. Gases can be
squeezed into a smaller space. In gases, the atoms or molecules have still
more energy and are free of one another except during occasional
collisions.
Molecules are in constant motion in all matter. All matter is made up of
particles. Gases, as well as solids and liquids, are made up of particles
that have mass and occupy space. In most solids, the particles are
arranged in repeating patterns. This arrangement forms crystals. Particles
of matter move faster as the matter is heated to increased temperatures.
The faster the particles move, the greater the force with which they bump
into, or collide with, other particles. Almost all matter expands as it
gets hotter and contracts when it cools.
Mass remains constant in a physical change in closed systems. The amount
of matter (stuff) remains the same, only the distance between the
particles and the motion of the particles change. In a closed system the
total mass of each element in the system remains constant before as well
as after any kind of chemical or physical change. Matter is not created or
destroyed during the change. Regardless of how substances within a closed
system interact with one another, or how they combine or break apart, the
total mass of the system remains the same. The idea of atoms explains the
conservation of matter. If the number of atoms stays the same no matter
how they are rearranged, then their total mass stays the same. Matter
changes states through melting (solid to liquid), freezing (liquid to
solid), evaporation (liquid to gas), and condensation (gas to liquid).
Dissolving is a physical change that results from the mixing of a solid in
a liquid. The molecules of the solid move apart and are mixed among the
molecules in the liquid. Dissolving is the formation of a mixture; it
usually does not require heating. Melting takes place when a pure solid
substance is heated to produce the liquid phase of the substance. When the
substance cools it will return to the solid state if it were in solid form
at room temperature.
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