8th grade · Science · Unit 1 of 10
Particles & Matter
Kinetic theory and the atom
What your child practices
How the movement of particles explains solids, liquids and gases and changes of state, the parts of an atom (including the quarks inside protons and neutrons, and electrons as leptons), elements and compounds, and telling physical from chemical changes.
Minnesota K-12 Academic Standards benchmark: 8P.1.2.1.1; 8P.3.2.1.1 · how adding or removing thermal energy changes a pure substance, explained with particles
How we explain it
Children can open this short lesson before they practice.
- Particles in solids vibrate in place; in liquids they slide; in gases they move freely.
- Melting, freezing, evaporation and condensation are changes of state. Condensation is gas to liquid.
- Atoms have protons and neutrons (made of quarks) in the nucleus, with electrons around it. An element has one kind of atom.
Example: Water droplets form on a cold glass. Which change of state is this? Water vapor in the air touches the cold glass. Gas becomes liquid. Answer: condensation
Particles & Matter in Minnesota
In the Minnesota K-12 Academic Standards, this is unit 1 of 10 in 8th grade Science, before Light & Radiation.
Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
Which particle has a negative charge?
- electron
- neutron
- nucleus
- proton
electron
Hint: Electrons are negative, protons positive and neutrons have no charge.
Question 2
A compound is…
- a mix of two liquids
- two or more elements chemically joined
- any metal
- a gas
two or more elements chemically joined
Hint: Water (H₂O) joins hydrogen and oxygen in a fixed ratio.
Question 3
Why do scientists keep changing their models of the atom?
- Atoms change shape every year.
- Scientists vote on a new model each decade.
- New evidence shows something the old model cannot explain.
- Old models were never tested.
New evidence shows something the old model cannot explain.
Hint: A model is the best explanation we have so far. It is revised when experiments give new evidence.
Question 4
Physical change or chemical change? Sort each example.
Sort into: 🧊 Physical change · 🔥 Chemical change
- 🪵a log burns
- 🍳an egg cooks
- 🧂salt dissolves in water
- 🔩an iron nail rusts
- ♨️water boils into steam
- 🧊ice melts
- 🥛a glass is smashed
- 🫧baking soda fizzes in vinegar
🧊 Physical change: salt dissolves in water, water boils into steam, ice melts, a glass is smashed · 🔥 Chemical change: a log burns, an egg cooks, an iron nail rusts, baking soda fizzes in vinegar
Hint: In a physical change the substance stays the same (just a different shape or state). In a chemical change a new substance forms.
Question 5
Why does a drop of food coloring spread faster in hot water than in cold water?
- Food coloring dissolves only in cold water.
- Hot water particles move faster and collide more.
- Cold water has no particles.
- Hot water is heavier.
Hot water particles move faster and collide more.
Hint: More particle motion means faster mixing (diffusion).
Question 6
Which is a physical change?
- Wood burning
- Milk turning sour
- Ice melting
- Iron rusting
Ice melting
Hint: In a physical change, no new substance forms.