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7th grade · Science · Unit 5 of 10

Particles & Mixtures

Pure substances and mixtures

What your child practices

The particle theory of matter, the states of matter, pure substances versus mixtures, and homogeneous versus heterogeneous mixtures.

Maine Learning Results learning standard: MS-PS1-4 · particle models of pure substances and mixtures

How we explain it

Children can open this short lesson before they practice.

  1. All matter is made of tiny particles that are always moving and have spaces between them.
  2. A pure substance has one kind of particle. A mixture has two or more.
  3. A homogeneous mixture looks the same all through; a heterogeneous one has parts you can see.

Example: Is salad dressing with oil floating on vinegar homogeneous or heterogeneous? You can see the separate layers. Visible parts mean heterogeneous. Answer: heterogeneous

Particles & Mixtures in Maine

In the Maine Learning Results, this is unit 5 of 10 in 7th grade Science, after Cycles & Succession and before How Plants Work.

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.

Source: Maine Department of Education

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Homogeneous or heterogeneous? Sort each mixture.

    Sort into: 🥛 homogeneous (looks the same throughout) · 🍕 heterogeneous (different parts show)

    • 🫙vinegar
    • 🌬️air in a clean room
    • 🍎clear apple juice
    • 🟤muddy water
    • 🥣cereal in milk
    • 🏖️iron filings mixed with sand

  2. Question 2

    According to the particle theory, all matter is made of…

    • heat and light
    • only atoms of metal
    • smooth material with no gaps
    • tiny particles

  3. Question 3

    What is a mixture?

    • A gas that cannot be seen
    • A new substance with new properties
    • Matter with only one kind of particle
    • Two or more substances physically combined, each keeping its own properties

  4. Question 4

    Brass is copper and zinc mixed evenly throughout a solid. It is a…

    • homogeneous mixture
    • pure substance because it is a solid metal
    • gas
    • heterogeneous mixture

  5. Question 5

    In which state of matter are the particles farthest apart?

    • solid
    • liquid
    • gas

  6. Question 6

    Cooking oil and water do not stay mixed. Both are pure, but together they form…

    • a homogeneous mixture
    • a single element
    • a new pure substance
    • a heterogeneous mixture

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