Standard 1/Middle School
substances as elements, compounds, or mixtures and justify classifications
in terms of atoms and molecules.
Matter consists of extremely
small, invisible particles called atoms. Atoms cannot be broken down into
their smaller parts during a physical change, or during a chemical
reaction. They can be broken into smaller particles during nuclear
reactions. All elements are made of one kind
of atom. See Periodic
Table of Elements.
Atoms may exist alone or be
combined together. When two or more atoms join together, they form
molecules. When different kinds of elements join together, they form compounds.
For example, oxygen exists
as a molecule containing two oxygen atoms in the atmosphere. When three
oxygen atoms join together, they form the molecule called ozone.
Water is a substance/ a
compound made of hydrogen and oxygen atoms. Each water molecule is made of
two atoms of hydrogen and one atom of oxygen.
These molecules/compounds do
not break down into individual atoms/elements when they are heated or
cooled during phase changes.
Molecules can be broken down
into separate atoms or simpler molecules when exposed to electrical current
or during a chemical reaction. Examples of chemical reactions include:
- a reaction with acids
- burning (a chemical reaction with oxygen. .
When two or more elements
and/or compounds are physically combined together, they are called a mixture. Mixtures can be physically separated
into their original components.
- Classify substances as elements, compounds,
- Justify their classifications in terms of
atoms and molecules.
See Molecular Structure of
solids, liquids, and gases, (SCI.IV.1.MS.4).
Key Concept / Real World Context / Instructional
Example / Assessment Example / Resources