Key Concepts
What are substances made of?
Repeating groups of atoms
What properties can change during a reaction?
Smell, color, state, melting/boiling point
What does mixing substances cause?
Atoms rearrange to form new substances
Why do scientists use diagrams?
To show atom groups
What’s one way to prepare for multiple choice?
Review diagrams & properties
What does it mean if two substances have different groups of atoms?
They have different properties
Two gases at room temperature—will their properties always be the same? Why?
No, it depends on their repeating groups of atoms.
What must remain the same in a reaction?
The total number of atoms
What should a correct model show?
Atoms rearranging into new groups
What’s a good way to practice written responses?
Use CER (Claim, Evidence, Reasoning)
Give one example of a property.
Smell, color, melting point, boiling point, etc.
Why do two solids look similar but have different properties?
They are made of different repeating groups of atoms
What happens to properties after a reaction?
They change
What’s wrong if a model shows extra atoms appearing?
That’s impossible — atoms can’t appear or disappear
Why practice explaining in your own words?
It helps understand how atoms rearrange
What happens to atoms in a chemical reaction?
They rearrange to form new substances
Name a property that can be measured with temperature.
Melting point or boiling point
Example: A red liquid and a solid make 2 white substances. What happened?
Atoms rearranged into new substances
Why might a model be wrong if properties don’t match?
It didn’t show correct rearrangement
What should you quiz yourself on?
Properties and atom groups
What is evidence of a chemical change?
New color, gas, solid, or new melting/boiling point
What property tells if a substance is solid, liquid, or gas?
State of matter at room temperature
Does anything escape in a sealed reaction?
No
What do models explain about ending substances?
Why their properties are different
How to prepare for model questions?
Check if atoms are rearranged correctly.