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← Unit 3: The Nature of Matter

SNC1W · Unit 3 test review

The Nature of Matter: Test Review

Everything for the Unit 3 test on one page: the key facts from all 8 lessons, the mistakes that cost the most marks, and a practice test that points you back to the lessons you need.

Key facts

Pure Substances and Mixtures

  • Matter is anything that has mass and takes up space.
  • A pure substance has one kind of particle: an element (one kind of atom) or a compound (two or more elements chemically joined in a fixed ratio).
  • A mixture contains substances physically mixed but not chemically joined; its composition can vary.
  • A mechanical mixture has visible parts; a solution looks the same throughout.
  • Mixtures can be separated by physical methods (filtering, evaporating, distilling, magnets); compounds need a chemical reaction.

Physical and Chemical Properties and Changes

  • A physical property can be observed without making a new substance; a chemical property describes how a substance reacts to form new substances.
  • Density: , usually in g/cm³ or g/mL (1 mL = 1 cm³).
  • Water has a density of about 1.00 g/mL: less dense objects float, denser objects sink.
  • A physical change keeps the same substance; a chemical change makes a new substance.
  • Five clues of a chemical change: new colour, gas formed, precipitate, heat or light, new odour. They are clues, not proof.
  • On Canadian household products, an octagon frame means the contents are dangerous and a triangle frame means the container is dangerous.

How Models of the Atom Developed

  • Dalton (1803): atoms are tiny, solid, indivisible spheres; atoms of each element are identical.
  • Thomson (1897): discovered the electron using cathode rays; plum pudding model.
  • Rutherford (1911): gold foil experiment showed the atom is mostly empty space with a tiny, dense, positive nucleus.
  • Bohr (1913): electrons occupy fixed energy levels (shells); explains line spectra.
  • Chadwick (1932): discovered the neutral neutron in the nucleus.
  • Modern quantum model: electrons are found in electron clouds (regions of probability) around the nucleus.

Protons, Neutrons, Electrons and Bohr-Rutherford Diagrams

  • Protons (+1) and neutrons (0) are in the nucleus and each have a relative mass of 1; electrons (−1) are in shells and have almost no mass.
  • Atomic number = number of protons; it identifies the element.
  • Neutrons = mass number − atomic number.
  • In a neutral atom, electrons = protons. Ion charge = protons − electrons.
  • For elements 1 to 20, shells hold a maximum of 2, 8, 8 and 2 electrons, filled from the inside out.
  • Isotopes have the same number of protons but different numbers of neutrons.

The Periodic Table

  • The modern periodic table is arranged in order of increasing atomic number.
  • A period is a horizontal row (7 periods); a group or family is a vertical column (18 groups).
  • Metals are left of the staircase line, non-metals to the right, and metalloids along it.
  • Metals are usually shiny, malleable, ductile and good conductors; non-metals are usually dull, brittle and poor conductors.
  • Group 1: alkali metals; group 2: alkaline earth metals; group 17: halogens; group 18: noble gases.
  • Elements in the same group have similar chemical properties.

Patterns in the Periodic Table

  • Valence electrons are the electrons in the outermost shell; they determine chemical behaviour.
  • Period number = number of occupied electron shells.
  • Groups 1 and 2 have 1 and 2 valence electrons; groups 13 to 18 have the group number minus 10 (helium has 2).
  • Metals lose electrons to form positive ions; non-metals gain electrons to form negative ions, reaching a full outer shell.
  • Alkali metal reactivity increases down the group; halogen reactivity decreases down the group.
  • Atoms get bigger down a group and smaller across a period from left to right.

Compounds and Chemical Formulas

  • A subscript gives the number of atoms of the element just before it; no subscript means 1.
  • A subscript after a bracket multiplies everything inside; a coefficient multiplies the whole formula.
  • Ionic compounds: usually a metal and a non-metal; electrons transferred; crystal lattice; high melting point; conduct when dissolved or melted.
  • Molecular compounds: non-metals only; electrons shared; separate molecules; lower melting points; usually poor conductors.
  • In an ionic compound the ion charges add to zero, which sets the ratio: and give .

Chemistry, Consumer Products and Society

  • A product's life cycle: raw material extraction, processing and manufacturing, transport, use, and end of life (reuse, recycling or disposal).
  • Impacts can be social (people and communities), environmental (air, water, land, living things) or economic (money and jobs).
  • Household hazardous waste belongs at a hazardous waste depot, not down the drain or in the garbage.
  • Green chemistry designs products and processes to reduce or eliminate hazardous substances from the start.
  • Emerging chemical technologies are driven by regulations, costs, scarce resources, consumer demand, health concerns and climate goals.

Where marks get lost

  • Calling air a pure substance because it looks the same everywhere. Air is a solution of nitrogen, oxygen, argon, carbon dioxide and other gases. (Pure Substances and Mixtures)
  • Thinking anything clear and colourless is pure. Tap water is clear but contains dissolved minerals and chlorine, so it is a solution. (Pure Substances and Mixtures)
  • Mixing up compounds and mixtures. In a compound the elements are chemically joined in a fixed ratio and the properties change completely (sodium is a reactive metal and chlorine is a toxic gas, yet sodium chloride is table salt). In a mixture each part keeps its own properties. (Pure Substances and Mixtures)
  • Calling oxygen gas a compound because each particle has 2 atoms. Both atoms are oxygen, so is still an element. (Pure Substances and Mixtures)
  • Calling dissolving a chemical change. When sugar dissolves, it is still sugar; evaporating the water gets it back. Dissolving is a physical change. (Physical and Chemical Properties and Changes)
  • Treating any bubbles as proof of a chemical change. Boiling water bubbles because liquid water turns into water vapour, which is a physical change. (Physical and Chemical Properties and Changes)
  • Dividing the wrong way in density. It is mass divided by volume, not volume divided by mass: 54 g in 20 cm³ is 2.7 g/cm³, not 0.37 g/cm³. (Physical and Chemical Properties and Changes)
  • Using the final water level as the volume in water displacement. The object's volume is the change: final level minus starting level. (Physical and Chemical Properties and Changes)
  • Thinking heavier objects always sink. A huge log floats and a tiny pebble sinks; what matters is density, not mass. (Physical and Chemical Properties and Changes)
  • Thinking that the gold foil experiment showed the atom is solid. It showed the opposite: most alpha particles passed through, so the atom is mostly empty space. (How Models of the Atom Developed)
  • Mixing up Thomson and Rutherford. Thomson found the electron (plum pudding); Rutherford found the nucleus (gold foil). (How Models of the Atom Developed)
  • Saying Bohr discovered the neutron. Bohr described energy levels in 1913; Chadwick discovered the neutron in 1932. (How Models of the Atom Developed)
  • Thinking older models were useless. Each one explained the evidence of its time, and the Bohr-Rutherford diagram is still used today to show electron shells. (How Models of the Atom Developed)
  • Using the mass number as the number of neutrons. The mass number counts protons and neutrons together, so subtract the atomic number: sodium-23 has 23 − 11 = 12 neutrons, not 23. (Protons, Neutrons, Electrons and Bohr-Rutherford Diagrams)
  • Changing the number of protons to make an ion. Ions form by gaining or losing electrons; changing protons would make a different element. (Protons, Neutrons, Electrons and Bohr-Rutherford Diagrams)
  • Getting the ion sign backwards. Losing negative electrons makes the ion positive; gaining electrons makes it negative. (Protons, Neutrons, Electrons and Bohr-Rutherford Diagrams)
  • Putting 8 electrons in the first shell. The first shell holds only 2: carbon is 2, 4, not 6. (Protons, Neutrons, Electrons and Bohr-Rutherford Diagrams)
  • Thinking isotopes are different elements. Carbon-12 and carbon-14 are both carbon, because both have 6 protons. (Protons, Neutrons, Electrons and Bohr-Rutherford Diagrams)
  • Mixing up periods and groups. Periods are rows (think of a sentence ending in a period, read across); groups are columns. (The Periodic Table)
  • Calling hydrogen an alkali metal because it is in group 1. Hydrogen is a non-metal gas. (The Periodic Table)
  • Saying all metals are solid or all non-metals are poor conductors. Mercury is a liquid metal, and graphite (carbon) conducts electricity. (The Periodic Table)
  • Thinking the table is ordered by atomic mass. Mendeleev used atomic mass, but the modern table uses atomic number. (The Periodic Table)
  • Confusing the symbol with the first letter of the name. Some symbols come from Latin names: Na (sodium), K (potassium), Fe (iron), Cu (copper), Ag (silver), Au (gold), Pb (lead). (The Periodic Table)
  • Saying atoms get bigger across a period because they gain electrons. The electrons go into the same shell while the nucleus gets more positive, so the atoms shrink. (Patterns in the Periodic Table)
  • Assuming every group gets more reactive going down. That is true for metals, but halogens get less reactive going down. (Patterns in the Periodic Table)
  • Counting all the electrons as valence electrons. Only the outermost shell counts: chlorine has 17 electrons but only 7 valence electrons. (Patterns in the Periodic Table)
  • Reading the group number as the valence electrons for groups 13 to 18. Subtract 10: group 16 has 6 valence electrons, not 16. (Patterns in the Periodic Table)
  • Applying a subscript to the wrong element. In the 2 belongs to oxygen only: 1 carbon and 2 oxygen atoms. (Compounds and Chemical Formulas)
  • Forgetting the bracket. In the 2 doubles both O and H, so there are 2 hydrogen atoms, not 1. (Compounds and Chemical Formulas)
  • Forgetting to multiply by the coefficient. has 4 hydrogen atoms and 2 oxygen atoms, not 2 and 1. (Compounds and Chemical Formulas)
  • Calling or a compound. They have two atoms of the same element, so they are elements. (Compounds and Chemical Formulas)
  • Thinking an ionic formula like NaCl shows one molecule. Ionic compounds form a lattice of ions; the formula shows only the ratio. (Compounds and Chemical Formulas)
  • Looking only at the use stage. An electric product may make no pollution while you use it, but its mining, manufacturing and disposal still have impacts. (Chemistry, Consumer Products and Society)
  • Pouring leftover chemicals down the sink because they disappear. They end up in water treatment plants and lakes, which are not designed to remove many of them. (Chemistry, Consumer Products and Society)
  • Thinking anything labelled bio or plant-based is harmless. Many plant-based plastics break down only in industrial composting facilities, not in a backyard or the ocean. (Chemistry, Consumer Products and Society)
  • Putting lithium-ion batteries in the garbage or recycling bin. They can start fires; take them to a battery drop-off. (Chemistry, Consumer Products and Society)

Practice test

24 questions from across the unit. Each one shows the lesson it comes from.

  1. Pure Substances and Mixtures
    1
    Which of these is a compound?
  2. Pure Substances and Mixtures
    2
    What physical method would you use to get pure water back out of salt water?
  3. Pure Substances and Mixtures
    3
    Name the type of mixture that looks the same throughout, such as air or tap water.
  4. Physical and Chemical Properties and Changes
    4
    A piece of metal has a mass of 39.5 g and a volume of 5.00 cm³. What is its density in g/cm³? Give your answer to two decimal places.
    g/cm³
  5. Physical and Chemical Properties and Changes
    5
    Which observation is the strongest evidence that a chemical change has happened?
  6. Physical and Chemical Properties and Changes
    6
    Why do lakes freeze from the top down, which lets fish survive the winter?
  7. How Models of the Atom Developed
    7
    Put these atomic models in the order they were proposed, from earliest to latest.
    1. 1Chadwick: neutrons in the nucleus
    2. 2Bohr: electrons in energy levels
    3. 3Rutherford: tiny dense nucleus
    4. 4Dalton: solid indivisible sphere
    5. 5Thomson: plum pudding with electrons
  8. How Models of the Atom Developed
    8
    What is the common name for Thomson's model of the atom?
  9. How Models of the Atom Developed
    9
    How did Chadwick know the particles he found had no charge?
  10. Protons, Neutrons, Electrons and Bohr-Rutherford Diagrams
    10
    Phosphorus has atomic number 15 and mass number 31. How many neutrons are in a phosphorus-31 atom?
    neutrons
  11. Protons, Neutrons, Electrons and Bohr-Rutherford Diagrams
    11
    What is the electron arrangement of a neutral silicon atom (atomic number 14)?
  12. Protons, Neutrons, Electrons and Bohr-Rutherford Diagrams
    12
    Why do carbon-12 and carbon-14 react the same way chemically?
  13. The Periodic Table
    13
    An element is shiny, can be hammered into a sheet and conducts electricity well. It is most likely a
  14. The Periodic Table
    14
    What is the family name of group 18, the very unreactive gases?
  15. The Periodic Table
    15
    Why are alkali metals stored under oil?
  16. Patterns in the Periodic Table
    16
    How many valence electrons does phosphorus (atomic number 15, group 15) have?
    valence electrons
  17. Patterns in the Periodic Table
    17
    Which halogen is the most reactive?
  18. Patterns in the Periodic Table
    18
    Going across period 3 from sodium to chlorine, the atoms
  19. Compounds and Chemical Formulas
    19
    How many atoms in total are in one molecule of table sugar, ?
    atoms
  20. Compounds and Chemical Formulas
    20
    Which compound is ionic?
  21. Compounds and Chemical Formulas
    21
    Why does a solution of table salt in water conduct electricity, while a solution of sugar does not?
  22. Chemistry, Consumer Products and Society
    22
    Put the stages of a product's life cycle in order.
    1. 1Recycling or disposing of the product
    2. 2Using the product at home
    3. 3Shipping the finished product to stores
    4. 4Mining the raw materials
    5. 5Refining materials and manufacturing the product
  23. Chemistry, Consumer Products and Society
    23
    Making aluminium cans from ore uses 2000 units of energy. Recycled aluminium uses about 95% less. How many units of energy does making the same cans from recycled aluminium use?
    units
  24. Chemistry, Consumer Products and Society
    24
    Which is the best example of a social impact of a product?

Endless drill

Fresh numbers every time, for the calculation questions in this unit.

Endless drillnew numbers every time

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