States & Particles
What is matter?
Anything that has mass and takes up space.
What is an atom?
The basic unit of an element; the smallest particle that still has the properties of that element.
In CO₂, how many oxygen atoms are present?
Two oxygen atoms.
Is O₂ an element, a molecule, or both? (short answer)
O₂ is both an element (made of oxygen atoms) and a molecule (two oxygen atoms bonded).
Give one example of a physical property students can observe (e.g., color, shape, mass).
Examples: color, shape, mass, hardness.
Describe how particles move in a solid.
Particles are close together and vibrate in place.
Name the three main subatomic particles and one place each is found
Protons (positive, nucleus), neutrons (no charge, nucleus), electrons (negative, electron cloud)
How many total atoms are in H₂O?
Three total atoms (2 H + 1 O).
Is H₂O an element or a molecule? (short answer)
H₂O is a molecule.
Give one example of a chemical property
Examples: flammability, reactivity with water or acid, ability to oxidize.
Describe how particles move in a liquid.
Particles move past one another and can slide.
What is a molecule? Give a simple example.
Two or more atoms chemically bonded together (example: H₂O).
How many hydrogen atoms are in CH₄?
Four hydrogen atoms.
What is an extended structure? (one sentence)
An extended structure is a large repeating arrangement of atoms or units (like a crystal lattice).
Describe a physical change and give one simple example
Physical change: shape or state changes but chemical identity stays same (example: ice melting to water).
Describe how particles move in a gas.
Particles are far apart and move freely in all directions.
Draw (or describe) a simple model of a water molecule showing atoms and labels.
Model: two H circles labeled H connected to one O circle labeled O; bonds shown as lines.
How many total atoms are in NH₃?
Four total atoms (1 N + 3 H).
Name one substance that has an extended structure and say why (one sentence).
Diamond — carbon atoms in a repeating network (or table salt — ions arranged in a repeating pattern).
Describe a chemical change and give one simple example
Chemical change: substances react to form new substances (example: iron rusting, baking causes new materials to form).
Give one example of how temperature affects particle motion
Example: When heated, particles move faster and spread out (e.g., ice melts into water).
Explain why scientists use models to study atoms and molecules (two to three sentences).
Scientists use models because atoms and molecules are too small to see; models help us show structure and predict behavior.
Explain what a subscript in a chemical formula tells you (one or two sentences).
A subscript tells how many atoms of that element are in the molecule; if no subscript, there is one.
Explain in two sentences why not all solids are made of separate molecules (use the idea of extended structures).
Some solids (like table salt or diamond) are extended networks of atoms or ions rather than separate molecules; their repeating bonds form one large structure.
You are given a sample before and after mixing substances. Name two observations that would tell you a chemical change happened
Observations indicating chemical change: color change, gas bubbles produced, temperature change without heating, or a new solid (precipitate) forms.