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The Particle Theory of Matter

Pure Substances vs. Mixtures

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Outcomes This slide show covers the following

course outcomes (refer to your “Outcomes” handout for Unit 3):› 3.1› 3.2› 3.3› 3.4› 3.5

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Pure Substances & Mixtures Complete the KWL chart below about

pure substances and mixtures.K

What you already know

WWhat you

wonder about

LWhat you learned

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Pure Substances (p.236) A pure substance is matter that is the

same throughout. According to the Particle Theory of Matter

(PTM):› All matter is made up of tiny particles.› The particles of one substance differ from the

particles of other substances. What does this mean for pure substances?

› We can infer that the particles in a pure substance are identical while the particles in a mixture are different.

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Pure Substances (con’t) To consider pure substances, let’s

consider our most important chemical: water.› Most of you should recognize the chemical

symbol H2O. What does this mean?› The symbol H2O refers to the parts of a

water particle: 2 parts hydrogen (H) to 1 part oxygen (O).

› So, if water contains hydrogen and oxygen, why is it considered a pure substance??

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The fact that water is a pure substance stems from the definition. That is, it is a substance that is the same throughout.› Q: If you took 10 drops of clear water and

looked at each drop under a microscope, what would you notice?

› A: Each drop is exactly the same! (Fig.7.5)

› Every water particle is identical – each particle contains 2 parts hydrogen and 1 part oxygen.

Pure Substances (con’t)

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Now, consider tap water.› Q: How would a drop of tap water

compare with a drop of pure water?› A: The drop of tap water would contain

water particles (H2O) but would also contain different particles such as chlorine, salt, dirt, etc.

› Since there is more than one type of particle, tap water is a mixture (see figure 7.7, p.237)

Mixtures vs. Pure Substances

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Summary A pure substance is matter that is the

same throughout.› Every particle in the substance is identical.› Examples: pure water, oxygen, carbon

dioxide A mixture is matter that contains more

than one type of particle.› Examples: tap water, air, soup

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Review Read pages 236-237. Complete the “Reading Check” (#1-3) on

page 237. Complete the “L” column in the KWL chart

to explain what you learned and to answer your “wondering” questions.

Research Question:› There are two types of pure substances:

elements and compounds. Define these terms and find a few common examples of each.