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Grade 7 · Science · Unit 7 of 12

Atoms & Elements

Elements, compounds and chemical symbols

What your child practises

Elements versus compounds and mixtures, chemical symbols (H, O, Na, Cl, Fe, Au…), counting atoms in formulas like H₂O and C₆H₁₂O₆, metals and non-metals, and the basics of the periodic table.

Ontario Curriculum expectation: C2.8 · elements and compounds as atoms and combinations of atoms

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

    What makes atoms of one element different from atoms of another element?

    • how fast they move
    • the temperature of the room
    • the number of protons in the nucleus
    • their colour
    Show answer

    the number of protons in the nucleus

    Hint: Every hydrogen atom has 1 proton; every carbon atom has 6. That number is the atomic number.

  2. Question 2

    How many different elements are in C₃H₈ (propane)?

    C₃H₈propane

    answer box

    Show answer

    2

    Hint: Each capital letter starts a new element symbol. Count the different symbols, not the small numbers.

  3. Question 3

    Elements in the same column (group) of the periodic table…

    • have similar chemical properties
    • were all discovered in the same year
    • are all gases
    • all have the same mass
    Show answer

    have similar chemical properties

    Hint: Groups are like families: sodium and potassium, in the same group, both react strongly with water.

  4. Question 4

    What is the chemical symbol for calcium?

    ⚛️calcium
    • C
    • Cm
    • Ca
    • Cl
    Show answer

    Ca

    Hint: Most symbols are the first one or two letters of the name (O for oxygen, Ca for calcium). Some come from Latin names: Na (natrium) for sodium, Fe (ferrum) for iron, Au (aurum) for gold, Ag (argentum) for silver, K (kalium) for potassium, Pb (plumbum) for lead, Hg (hydrargyrum) for mercury, Sn (stannum) for tin.

  5. Question 5

    Element, compound or mixture? Sort each substance.

    Sort into: ⚛️ element · 🧪 compound · 🥣 mixture

    • 🥗fruit salad
    • 💧water (H₂O)
    • 🟡gold (Au)
    • 🪴garden soil
    • 🧂table salt (NaCl)
    • 🎈helium (He)
    Show answer

    ⚛️ element: gold (Au), helium (He) · 🧪 compound: water (H₂O), table salt (NaCl) · 🥣 mixture: fruit salad, garden soil

    Hint: An element has only one kind of atom. A compound has different elements chemically joined in a fixed ratio. A mixture is substances mixed together but not chemically joined.

  6. Question 6

    What is an element?

    ⚛️
    • Any liquid that conducts electricity
    • A mixture that can be separated by filtering
    • A substance made of two or more different kinds of atoms joined together
    • A pure substance made of only one type of atom
    Show answer

    A pure substance made of only one type of atom

    Hint: Gold contains only gold atoms; oxygen contains only oxygen atoms. That's what makes them elements.

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