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3.1Elements, Compounds and Mixtures

Elements, Compounds and Mixtures

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Lesson summary

3.1 Elements, Compounds and Mixtures — CHECKPOINT (CHEMISTRY) notes: Distinguish elements, compounds and mixtures.Element = a substance made of just one kind of atom, e.g.

  • Properties
  • Arrangement
  • Composition
  • Pure substance
  • Iron sulfide
  • Element = a substance made of just one kind of atom, e.g. carbon, gold, silver

Section 1 of 7Elements

  • Element = a substance made of just one kind of atom, e.g. carbon, gold, silver
  • Properties
    • each type of atom has different properties, so different elements have different properties
  • Arrangement
    • atoms in neon move freely, atoms in metals such as gold are packed closely, and in oxygen and sulfur atoms join in small particles
    • An oxygen particle has two atoms; a sulfur particle has eight.

Section 2 of 7Compounds

1Compound
= a substance in which two or more different kinds of atom are bonded together
2Bonding1 point
= the tight joining of atoms
  • Sodium atoms bonded with chlorine atoms form sodium chloride.
3Properties2 points
  • a compound has totally new properties, different from the elements it is made from
  • Sodium chloride is common salt, unlike sodium or chlorine.

Section 3 of 7Particle diagrams

  • Element
    • all the atoms in a particle are the same (oxygen, O2)
  • Compound
    • different kinds of atom are bonded together (carbon dioxide CO2, water H2O, methane CH4)
  • Test
    • if different kinds of atom are bonded in the particle diagram, the substance is a compound

Section 4 of 7Mixture compared with compound

FeatureMixture of iron and sulfurCompound iron sulfide
BondingNot bondedAtoms bonded
PropertiesEach substance keeps its own propertiesNew properties
SeparationMagnet removes the ironCannot be removed with a magnet

Section 5 of 7Pure substances and mixtures

  • Pure
    • a pure substance contains a single substance only, e.g. pure water
  • Mixture
    • made of different kinds of particle mixed together; may contain elements, compounds or both

Section 6 of 7Air is a mixture

  • Composition
    • about 78% nitrogen, 21% oxygen and 1% carbon dioxide, argon, water vapour and other gases
  • Varies
    • the amount of water vapour changes with the weather
    • Plants and animals change carbon dioxide levels by respiring and by photosynthesis.
    • Burning fossil fuels increases carbon dioxide.
  • History
    • the composition of air has changed over millions of years; there was once much less oxygen

Section 7 of 7Separating a mixture

  • Properties
    • a mixture can be separated by physical means because each substance keeps its properties
  • Compound
    • needs a chemical reaction to be split

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