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9th grade · Science · Unit 4 of 10

Electrons & Compounds

Why atoms bond and what they make

What your child practices

How valence electrons decide whether atoms gain, lose or share electrons, ionic and covalent compounds, and reading simple chemical formulas.

Maine Learning Results learning standard: HS-PS1-1; HS-PS1-2 · how outer electrons explain bonding and chemical reactions

How we explain it

Children can open this short lesson before they practice.

  1. Atoms gain, lose or share electrons to get a full outer shell.
  2. Metals lose electrons and non-metals gain them to form ionic compounds, like sodium chloride.
  3. Non-metals share electrons to form covalent compounds, like water (H₂O).

Example: Which pair most likely forms an ionic compound: carbon and oxygen, or potassium and chlorine? Ionic compounds form between a metal and a non-metal. Potassium is a metal; chlorine is a non-metal. Answer: potassium and chlorine

Electrons & Compounds in Maine

In the Maine Learning Results, this is unit 4 of 10 in 9th grade Science, after Atoms & Electrons and before Photosynthesis & Respiration.

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

    Which pair would most likely form an ionic compound?

    • sodium and chlorine
    • nitrogen and hydrogen
    • hydrogen and hydrogen
    • carbon and oxygen

  2. Question 2

    Which pair would most likely form a covalent compound?

    • potassium and bromine
    • sodium and chlorine
    • calcium and oxygen
    • carbon and oxygen

  3. Question 3

    Which type of bond forms when electrons are transferred from a metal to a non-metal?

    • physical
    • covalent
    • ionic
    • nuclear

  4. Question 4

    Ionic or covalent? Sort each compound.

    Sort into: ⚡ Ionic · 🤝 Covalent

    • 🧊CaCl₂ (calcium chloride)
    • 🌫️CO₂ (carbon dioxide)
    • 🧂NaCl (table salt)
    • 🧴NH₃ (ammonia)
    • 🧪KBr (potassium bromide)
    • 💧H₂O (water)
    • ⚗️MgO (magnesium oxide)
    • 🔥CH₄ (methane)

  5. Question 5

    What charge does an ion of a Group 2 element (like calcium) usually have?

    • −2
    • 0
    • +2
    • +1

  6. Question 6

    What does the formula CO₂ tell you?

    • Two carbon atoms and one oxygen atom
    • Carbon is an oxygen ion
    • Carbon dioxide is an element
    • One carbon atom and two oxygen atoms are in each molecule.

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